rsna syllabus radiation biology 2007

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2007 Syllabus:Radiation Biology for Diagnosticand Interventional Radiologists

Wayne R. Hedrick, PhD, Editor Canton, Ohio

Mahadevappa Mahesh, PhD, Contributor Baltimore, Maryland

5th Edition

Radiation Biology Syllabus for Diagnostic and Interventional Radiologists� 2007

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Contents

�2007 Radiation Biology Syllabus for Diagnostic and Interventional Radiologists

Preface

For the fifth edition of the syllabus, the general format of the fourth edition has

been retained, with various topics updated. The principal change in format is the addition of references to support the correct answers. Informational content has been expanded to include magnetic resonance (MR) imaging and ultrasound. Current recommendations by the American College of Radiology with respect to safe MR practices are included. Questions are classified in the following sections: Radiation Biology/Effects, Radia-tion Safety/Protection, Magnetic Resonance Imaging, and Ultrasound. The conversion to a Web-based instructional publication will facilitate future and more frequent revisions.

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Radiation Biology Syllabus for Diagnostic and Interventional Radiologists� 2007�

A Only one answer is correct B Match answers X True/False–any number of answers may be True

Questions

Instructions for Sample Questions

Each question is one of the following types, as indicated immediately preceding the question:


I.RadiationBiology/Effects

A1. The majority of the energy received by

biologic material from x rays is transferred by

A. ElectronsB. Degraded gamma photonsC. Protons D. Spallation products

A2. The percentage of x-ray damage to biologic

material mediated by free radicals is closest to

A. �0%B. �0%C. �0%D. 60%E. 90%

A3. X-ray–produced chromosomal aberrations,

such as dicentrics and rings, are generated as a consequence of

A. A single chromosomal break interacting with itself

B. Interaction of two separate chromosomal breaks

C. High-dose events caused by a single electron

D. Misreplication events

A4. Cell killing by x rays correlates best with

A. Damage to DNA basesB. The initial number of DNA double-strand

breaksC. The final number of DNA double-strand

breaksD. The number of thymine dimers

X 5. Which of the following statements concerning

chromosomal aberrations in stimulated peripheral lymphocytes are true?

A. They can be used to assess whole-body radiation exposures

B. They can be used to detect a dose of � cGyC. They can be used to measure a total body

dose of �0 Gy � weeks after exposureD. The number of interchange aberrations is a

linear function of dose for x rays

X 6. Chromosome changes induced by radiation

include

A. Acentric fragmentsB. Centric fragmentsC. InversionsD. Symmetric translocationsE. Dicentrics

A7. The phase of the cell cycle that is most variable

in length is

A. G�B. G�C. MD. S

A8. If an asynchronous population of cells is

exposed to a single x-ray dose of �0 Gy, the surviving cells are partly synchronized because

A. Radiation block occurs in the G� phaseB. Radiation block occurs in the S phaseC. Most survivors are in the G� phaseD. Most survivors are in the late S phase

�2007 Radiation Biology Syllabus for Diagnostic and Interventional Radiologists2007


A9. The most radiosensitive portion of the

gastrointestinal tract to cell killing is the

A. EsophagusB. StomachC. Small intestineD. Large intestineE. Oropharynx

A10. The syndrome that is associated with the

greatest sensitivity to x rays is

A. Bloom syndromeB. Ataxia telangiectasiaC. Fanconi anemiaD. Xeroderma pigmentosum

A11. The shoulder in cell survival curves is MOST

pronounced when cells are irradiated with

A. �-MeV neutronsB. �-MeV alpha particlesC. �-MeV electronsD. �00-MeV pi mesons

A12. For a given total dose of x rays, a protracted

exposure at a low dose rate is less effective in killing mammalian cells than an acute exposure at a high dose rate, primarily because

A. Fewer free radicals are producedB. The mitotic cell cycle is shortenedC. Cell division occurs during exposureD. Ion pairs recombine during extended

exposureE. Repair of sublethal damage occurs during

exposure

X 13. The likelihood of late stochastic effects following

exposure to radiation is influenced by

A. Radiation doseB. Linear energy transfer (LET) of the radiationC. Radiation dose rateD. Type of tissue exposed

A14. The minimum dose range that results in an

expected �%–�0% prevalence of nausea following acute total-body irradiation is

A. 0.0�–0.� GyB. 0.�–0.�� GyC. 0.7�–�.�� GyD. More than �0 Gy

A15. The most likely consequence of an acute total

body exposure to � Gy of x rays is

A. DiarrheaB. Decrease in lymphocyte countC. EpilationD. Sterility in a femaleE. Erythema

B16. Match the items (�–�) with the doses (A–D)

(single acute x-ray exposures).

�. Dose producing the cerebrovascular syndrome

�. Estimated dose to double the natural mutation rate

�. Typical LD �0/� (ie, gastrointestinal death)�. Typical LD �0/60 in humans

A. �00 GyB. �0 GyC. � GyD. � Gy

Radiation Biology Syllabus for Diagnostic and Interventional Radiologists6 20076


X 17. Which of the following effects would be seen as

a consequence of a total body exposure to �.� Gy of x rays?

A. Vision-impairing cataracts of the ocular lens

B. Dicentric chromosomes in peripheral lymphocytes

C. Skin erythemaD. AtaxiaE. Increased carcinogenesis from ��% to �0%

X 18. An acute whole-body exposure of � Gy of low-

LET radiation will cause which of the following effects?

A. Vomiting in 9�% of those exposedB. Diarrhea in 9�% of those exposedC. Temporary sterility in malesD. Permanent sterility in femalesE. Decrease in lymphocyte count


total body irradiation of humans after an acute exposure to x rays are true?

A. The LD �0/60 is between � and � GyB. Seizures are likely if the dose exceeds � GyC. The nadir in white cell count following a

dose of � Gy will occur within 6 daysD. Bone marrow transplants are likely to save

persons exposed to more than �� Gy

A20. The earliest clinically detectable effect of

radiation on the skin is

A. EpilationB. PainC. UlcerationD. ErythemaE. Depigmentation

X 21. Which of the following are true concerning

radiation-induced sterility?

A. An acute 0.�-Gy dose of gamma rays can induce temporary sterility in males

B. An acute �.�-Gy or greater dose of gamma rays can induce permanent sterility in females

C. Radiation-induced permanent sterility in males leads to a loss of libido

D. Radiation-induced sterility in females produces hormonal changes

E. An acute �-Gy dose of gamma rays will cause immediate sterility in males (ie, no latent period)


radiation-induced heritable effects are true?

A. Radiation-induced heritable changes are different from those that occur spontaneously

B. Humans are much more sensitive to radiation than mice

C. Risk estimates in humans are based largely on data from mice

D. �0%–�0% of heritable changes in the population can be attributed to background radiation

E. The doubling dose in humans is estimated to be 0.�–�.� Sv (acute exposure)

A23. A patient undergoes two CT scans of her abdo-

men; the dose was 0.� Gy. If she subsequently becomes pregnant within � year, what is the probability that the child will have a radiation-induced hereditary defect?

A. Less than � in �,000B. � in �,000 to � in �00C. � in �00 to � in �0D. > �0%

72007 Radiation Biology Syllabus for Diagnostic and Interventional Radiologists2007


A24. The dose-response relationship for solid

tumors in the Japanese survivors used by the BEIR V and UNSCEAR committees has the form

A. Linear with no thresholdB. Linear with thresholdC. Quadratic with no thresholdD. ExponentialE. Quadratic with threshold

A25. Which of the following organs in children is

most sensitive to the induction of both benign and malignant tumors by x rays?

A. Bone marrowB. BreastC. ThyroidD. Lung

A26. Based on cancer risks in the BEIR V commit-

tee report, the number of cancer deaths in the general public in the United States as a result of nuclear power plant accidents is estimated to be closest to

A. �B. �0C. �00D. �,000

A27. The International Commission on Radiological

Protection (ICRP) estimate of the total number of cases of cancer of all types produced by a total body exposure of a working population to � Sv of low-LET radiation at a low dose rate is closest to

A. � in �00B. � in �,000C. � in �0,000D. � in �00,000

B28. Match the type of exposure (�–�) with the type

of radiation-induced cancer (A–E).

�. Patients who are treated with radiation for ankylosing spondylitis

�. Patients who undergo fluoroscopy repeatedly during management of tuberculosis

�. Uranium workers�. Dial painters who work with radium�. Marshall Island inhabitants

A. LeukemiaB. Breast cancerC. Thyroid cancerD. Lung cancerE. Bone cancer

B29. For each organ (�–�), select the correct

description of cancer incidence in the U.S. population (A–D).

�. Prostate�. Thyroid�. Breast�. Kidney

A. Low natural–low radiogenicB. Low natural–high radiogenicC. High natural–high radiogenicD. High natural–low radiogenic

X 30. A �-Gy exposure to a developing embryo when

radiation is administered during

A. weeks 8–�� of gestation is likely to induce abortions

B. weeks 0–� of gestation usually produces congenital abnormalities

C. weeks ��–�� can produce mental retardationD. weeks �–6 is likely to induce congenital

abnormalities

Radiation Biology Syllabus for Diagnostic and Interventional Radiologists8 20078



radiation-induced stochastic effects are true?

A. The clinical severity of the effect increases with dose

B. The probability that an individual will experi-ence the effect increases with dose

C. There is a well-defined threshold in doseD. The effect may arise from damage to a

small number of cells

X 32. Which of the following statements regarding

the study of the atomic bomb survivors in Hiroshima and Nagasaki are true?

A. Less than �,000 excess radiation-induced malignancies were found

B. There was an increased risk of radiation- induced breast cancer

C. There was an increased incidence of men-tal retardation in children exposed in utero

D. No statistically significant excess heritable effects in children of those exposed were found

X 33. Risk estimates for radiation-induced cancer in

humans are based on studies involving

A. Patients treated with I-�� for hyperthyroidismB. Survivors of Hiroshima and NagasakiC. Women developing breast cancer after

multiple fluoroscopic examinations for tuberculosis

D. Populations living near nuclear power plants


radiation oncogenesis are true?

A. Generally, the mean latent period for radia-tion-induced leukemia is about �0 years

B. Children are less sensitive than adults to the induction of leukemia

C. Benign neoplasms can be induced after irradiation

D. Solid tumors induced by radiation may appear �� years or more after exposure

E. A whole-body dose of 0.� Gy would be expected to increase the incidence of cancer from approximately �0% (the natural incidence) to approximately �0%

B35. Match the consequence (�–�) with the stage

of pregnancy (A–C) when radiation would most likely be the cause.

�. Congenital malformations (other than in the central nervous system)

�. Death�. Increased risk of cancer

A. PreimplantationB. OrganogenesisC. Fetal period

X 36. A therapeutic dose of I-�� to a patient with

Graves disease who is � weeks pregnant will

A. Not result in hypothyroidism in the fetusB. Cause intrauterine demise with 90%

probabilityC. Result in a �% risk of leukemia in the

motherD. Result in a �0% risk of solid tumors in the

mother

92007 Radiation Biology Syllabus for Diagnostic and Interventional Radiologists2007


X 37. A woman involved in a traffic accident com-

plained of lower back pain and underwent anteroposterior and lateral lumbosacral spine radiography. She was subsequently found to be �0 weeks pregnant. Which of the following are true?

A. The radiographs should not have been obtained

B. A therapeutic abortion should be recommended

C. If a radiation-induced defect occurs, it will most likely affect the central nervous system

D. The offspring may be at increased risk for a childhood malignancy

E. The fetus probably received an absorbed dose of 0.�–0.�� Gy

X 38. A woman receives a dose of �0 mGy to the

abdomen and pelvis and then learns she is �8 weeks pregnant. There is

A. An increased risk of intrauterine deathB. An increased risk of neonatal deathC. A risk of microcephaly in the infantD. A risk of leukemia in the child

A39. A ��-year-old woman undergoes cerebral angi-

ography and a CT scan of the brain involving �-mm-thick sections that include the orbits. The patient’s lifetime risk probability for radiation-induced cataracts is estimated to be

A. 0%B. 0.0�%C. 0.�%D. �.0%E. �0.0%


radiation-induced cataracts are true?

A. Cataracts begin in the anterior portion of the lens

B. A dose of � Gy over � years is likely to pro-duce a cataract

C. Prescription eyeglasses protect from 80% of the dose to the lens from diagnostic x rays

D. Vision-impairing cataracts are preceded by asymptomatic opacities in the lens.


radiation-induced cataracts are true?

A. A cataract is a stochastic effectB. The minimum single acute dose of x rays

that will produce a cataract is � GyC. A single dose of radiation is more likely to

induce a cataract than the same amount of radiation administered in �0 fractions

D. For a given dose, neutrons are more effective than gamma rays in producing cataracts

X 42. The explosion of a “dirty bomb” made from

highly radioactive material, such as a cobalt-60 teletherapy source, can result in which of the following?

A. Radiation dose sufficient to cause acute radiation injury

B. Casualties contaminated with radionuclidesC. Psychologic impact on the victimsD. Casualties may present a potential hazard

to medical personnel

Radiation Biology Syllabus for Diagnostic and Interventional Radiologists�0 2007�0


II.RadiationSafety/Protection

X 43. Which of the following units are SI units?

A. RadB. RemC. SievertD. CurieE. Gray

X 44. A pregnant, occupationally exposed woman

working in fluoroscopy shows a reading of � mSv over 90 days to a badge worn on her collar over a lead apron. Which of the following are true?

A. The Nuclear Regulatory Commission should be called

B. She should no longer work with fluoroscopyC. The dose recorded does not exceed

National Council on Radiation Protection and Measurements (NCRP) recommendations

D. A therapeutic abortion is recommended

A45. Which of the four pie charts (A–D) best de-

scribes the distribution of effective doses to the U.S. population as summarized by the NCRP?

A46. The biggest contributor to the effective dose to

the U.S. population from natural causes is

A. Cosmic radiationB. Solar radiationC. RadonD. Potassium-�0 in foodE. Gamma ray emitters in building materials

A47. In the United States, the greatest source of

exposure to ionizing radiations (collective ef-fective dose) in the general population due to human activity is

A. Video display terminalsB. Fallout from nuclear weapons testingC. Nuclear waste disposal sitesD. Medical and dental diagnostic radiationE. Nuclear reactor accidents

B48. Match the quantities (�–�) with the doses

(in millisieverts) (A–D).

�. Average background radiation in the United States, including radon

�. Dose limit per month (NCRP) to an occupa-tionally exposed worker who has declared her pregnancy

�. Dose received in flying across the Atlantic in a commercial jetliner

�. Genetically significant dose from medical radiation in the United States

A. 0.0�B. 0.��C. 0.�0D. �.0

��2007 Radiation Biology Syllabus for Diagnostic and Interventional Radiologists2007


X 49. Which of the following statements regarding

radon are true?

A. Concentrations are higher in the basement of a house than outside

B. The BEIR VI committee estimates that radon is the cause of �0% of lung cancer cases in the United States

C. Decay of radon involves emission of alpha particles

D. The half-life is �,600 yearsE. The parent is radium


radon are true?

A. Radon is a naturally occurring radioactive gas

B. Radon contributes a larger average effec-tive dose to the U.S. population than do medical x rays

C. The action level recommended by the EPA is � pCi/L

D. The half-life of radon is �,600 yearsE. The effective radiation emitted by radon

daughters is in the form of gamma rays

A51. Which of the following procedures is likely to

result in the greatest radiation exposure of personnel?

A. Chest radiograph obtained with a technolo-gist in the room

B. One CT section obtained with a technolo-gist in the room

C. Fluoroscopy of the abdomen for � minutesD. Knee examination with MR imaging

X 52. A genetically significant dose due to medical

x rays involves the

A. gonad dosesB. age and sex of the patientC. number of persons exposedD. time of day at which the exposure is

received

A53. A worker in a nuclear medicine laboratory

declares that she is � months pregnant. What is the NCRP recommended limit for the remainder of the pregnancy?

A. NoneB. 0.0� mSv/moC. 0.� mSv/moD. � mSv totalE. �0 mSv total

X 54. For radiation protection purposes,

A. the maximum permissible dose for hands reflects concern for cancer

B. a whole-body low-dose-rate exposure has a cancer risk of �%/Sv

C. hands are nearly as radiosensitive as the eyeD. low-dose-rate exposures are associated

with a lower risk of cancer development than high-dose-rate exposures

B55. For each of the following terms related to

radiation protection (�–�), select its appropriate definition (A–D).

�. Genetically significant dose�. Equivalent dose�. Effective dose�. Committed equivalent dose

A. Dosimetric term used when the source of radiation exposure is from radioactive mate-rial located within the body

B. The absorbed dose multiplied by a radiation weighting factor (Wr) appropriate for the type of radiation

C. An index of the presumed effect of gonadal irradiation on the whole population

D. The sum of the equivalent doses, weighted for the relative risk of cancer and hereditary effects, for all irradiated organs and tissues

Radiation Biology Syllabus for Diagnostic and Interventional Radiologists�� 2007��


B56. For each type of exposure (�–�), select the

appropriate current NCRP-recommended maximum permissible dose (A–D). (The choices A–D may be used more than once.)

�. Annual occupational effective dose limit�. Annual public equivalent dose limit (frequent

exposure)�. Monthly equivalent dose limit to a fetus

after a pregnancy has been declared�. Annual occupational equivalent dose limit

for the lens of the eye

A. 0.� mSvB. � mSvC. �0 mSvD. ��0 mSv

B57. Match the quantities (�–�) with the corresponding

units (A–D).

�. Absorbed dose�. Activity�. Equivalent dose�. Collective effective dose

A. SievertB. GrayC. Person-sievertD. Becquerel

A58. The NCRP maximum permissible dose for the

hands of radiation workers is based on

A. estimates for cancer induction of the basal layer of the skin

B. effects anticipated after acute exposuresC. epidemiologic studies of nuclear power

plant employeesD. concern for deterministic effects

X 59. Which of the following are NCRP recommen-

dations concerning occupational exposure?

A. No occupational exposure is allowed before the age of �8 years

B. Medical radiation received by radiation work-ers is included in their maximum permissible dose

C. ALARA (as low as reasonably achievable) does not apply to occupational exposure

D. The purpose of the occupational maximum dose is to protect against both stochastic and deterministic effects

X 60. Which of the following are considered patient

dose-reduction techniques during interventional fluoroscopy?

A. Increased source-to-skin distanceB. Use of last-image holdC. Variable pulse rate fluoroscopyD. Increased beam filtrationE. Removal of gridF. Dose spreadingG. Use of electronic magnificationH. Use of geometric magnification

A61. Which of the following is (are) considered to

offer minimum protection to the fluoroscopist?

A. Protective lead apronsB. Thyroid collarsC. Ceiling-mounted lead glass shieldD. Radiation-attenuating surgical gloves



A62. Which potential adverse effect is expected

to occur following a fluoroscopically guided interventional procedure in which a skin dose of �� Gy was delivered to a single site?

A. No visible effectB. Temporary hair loss within �� hoursC. Dry desquamationD. Damage to vascular structures

A63. Which of the following imaging procedures for

a pregnant patient will deliver the highest radiation dose to her 6-week-old fetus?

A. Abdominal ultrasoundB. Chest radiography (posteroanterior and

lateral projections)C. Head CT (with and without contrast

material)D. Kidney, ureter, bladder (KUB) radiography

(four radiographs)

A64. Which of the following work activities is not

recommended for a pregnant radiation worker?

A. Nuclear medicine imagingB. Radioactive iodine treatmentsC. FluoroscopyD. Portable radiography

III.MagneticResonanceImaging

A65. The usage of conventional metal detectors in

MR environments is NOT recommended by the American College of Radiology (ACR). The basis for this recommendation considers all of the following except ________.

A. Metal detectors are not necessary because low fringe fields exist with modern actively shielded superconducting magnets

B. Metal detectors do not differentiate between ferromagnetic and nonferromagnetic metallic objects/implants/foreign bodies

C. Metal detectors cannot detect a small metal fragment in the orbit or near the heart

D. Metal detectors have variable sensitivity response

A66. What is the ACR recommendation regarding

the pregnant MR imaging technologist or other health care practitioner working in the MR environment?

A. Permitted to work in and around the MR environment during the second and third trimesters only

B. Permitted to work in and around the MR environment throughout all stages of pregnancy

C. Permitted to remain in the magnet room during actual data acquisition/imaging

D. Should not enter the magnet room in response to an emergency



A67. What is the ACR guideline regarding the MR

imaging of pregnant patients?

A. Pregnant patients can be accepted to undergo MR imaging at any stage of preg-nancy

B. Pregnant patients should not undergo MR imaging during the first trimester

C. Gadolinium-based MR contrast agents can be routinely administered to pregnant patients

D. Fast MR imaging sequences, such as echo-planar imaging, should be avoided

X 68. Nephrogenic systemic fibrosis (NSF) has been

associated with administration of gadolinium-based MR contrast agents to patients with re-nal disease. What guidelines are recommended by the ACR when considering administering gadolinium-based MR contrast agents to a patient?

A. Hematologic screening for glomerular filtra-tion rate (GFR) prior to MR imaging

B. No special treatment for patients with stage � or � chronic kidney disease

C. Refrain from administering gadolinium-based MR contrast agents to patients with stage �, �, or � renal disease

D. Immediate hemodialysis following admin-istration of gadolinium-based MR contrast agents should be considered for any patient with severe or end-stage renal disease

A69. The presence of all the following metallic objects/

devices is considered a contraindication for MR imaging examination (meaning performance of MR imaging is not routine) except ________.

A. Implantable cardioverter-defibrillatorB. Implanted cardiac pacemakerC. Intracranial aneurysm clips composed of

titaniumD. Ferromagnetic foreign body in the eyeE. Swan-Ganz catheters

A70. What is a quench with respect to the supercon-

ducting magnet?

A. Uncontrolled loss of superconductivityB. Rapid boil-off of cryogensC. Requires the immediate evacuation of the

patient and personnel from the magnet room

D. All of the above

A71. According to the Food and Drug Administration

(FDA), a controlled access area must be estab-lished such that the fringe field outside this area does not exceed ________. For the safe operation of pacemakers, the magnetic field should be less than this value.

A. �0 GB. � GC. � GD. 0.� G

X 72. In �988, the FDA reclassified MR diagnostic

imagers as class II devices. New devices brought to the market had to demonstrate only that they were “substantially equivalent” to MR devices presently on the market. Safety guidelines pertaining to clinical MR imaging issued by the FDA include which of the following?

A. Static magnetic field strengthB. Time-varying magnetic fieldsC. Radiofrequency (RF) power depositionD. Acoustic noise levels



A73. The specific absorption rate (SAR) in units of

watts per kilogram describes ________.

A. Tissue heating induced by changes in magnetic field gradients

B. Absorption of transmitted RF energy by tissue

C. Attenuation of MR imaging signal by the patient

D. Attenuation of the applied static magnetic field within the patient

A74. What is the principal source of MR-generated

acoustic noise during MR imaging?

A. Cryogen reclamation systemB. Room air conditionersC. Vibrations of the gradient coilsD. Thermoelastic expansion caused by the

absorption of RF energy in the head

A75. Current MR imagers produce time-varying

magnetic fields (dB/dt), which can result in ________ in some patients.

A. Induction of intense pain (brain stimulation)B. Cardiac stimulationC. Peripheral nerve stimulationD. All of the above

A76. Local thermal injury to a patient during MR

imaging can be caused by ________.

A. Disconnected surface coil lead left on the patient

B. Patient contact with the inner bore of the magnet

C. Patients crossing their arms or legs in the MR imager

D. Implanted metallic foreign objects in the patient

E. All of the above

A77. What deleterious biologic effects are associ-

ated with chronic exposure to magnetic field strengths produced by MR imagers (0.�–� T)?

A. Peripheral nerve stimulationB. LeukemiaC. Congenital malformationsD. None

IV.Ultrasound

A78. At the point of interest in the ultrasonic field,

the instantaneous intensity is directly propor-tional to the square of the ________.

A. Acoustic pressureB. Acoustic velocityC. FrequencyD. Mass density

A79. Which of the following describes intensity mea-

surements using the unit of the decibel?

A. Based on a logarithmic scaleB. Measure of relative intensityC. A factor of two reduction in intensity corre-

sponds to a �-dB changeD. Point of interest may be greater or less than

the reference valueE. All of the above



A80. In �99�, the American Institute of Ultrasound

in Medicine (AIUM) and the National Electrical Manufacturers Association (NEMA) adopted the voluntary standard for the display of acoustic output information called the output display standard (ODS). What two acoustic output parameters, shown in real time on the monitor, were defined as indicators of the potential for biologic effect?

A. Derated power and scan timeB. Acoustic intensity averaged over the focal

area and duty factorC. Mechanical index and thermal indexD. Intensity index and thermal index

A81. In ultrasound, the acoustic output parameter

thermal index (TI) indicates ________ for the current scanning parameters.

A. Maximum temperature rise in tissueB. Minutes of exposure time before heating is

too greatC. Likelihood of inducing cavitationD. Acoustic power in milliwatts

A82. As the ultrasound beam propagates through

tissue, the intensity decreases as sonic energy is absorbed and converted into heat. What factor(s) affect(s) the rate of temperature rise in tissue?

A. Temporal average intensityB. FrequencyC. Duration of exposureD. Pulse repetition frequencyE. All of the aboveF. B, D

A83. As the ultrasound beam propagates through

tissue, the intensity decreases as sonic en-ergy is absorbed and converted into heat. The increased temperature has the potential to cause irreversible tissue damage. The biologic response is a ________ phenomenon.

A. Nonthreshold linearB. Nonthreshold quadraticC. Threshold (temperature only)D. Threshold (temperature and time)

A84. Which of the following real-time scanner set-

tings can affect the acoustic output index?

A. Time-gain compensationB. Frame rateC. Transmit powerD. FrequencyE. Gray-scale mappingF. All of the aboveG. A, C, DH. B, C, D

A85. The output display standard of mechanical

index (MI) increases in magnitude as the ________ is decreased.

A. Acoustic pressureB. Acoustic velocityC. FrequencyD. Peak intensity

A86. According to the AIUM statement on “Mam-

malian In Vivo Ultrasonic Biological Effects,” no independently confirmed significant biologic effects have occurred with spatial peak, tem-poral average intensities below ________ for mammalian tissues exposed in vivo. Assume focused ultrasound.

A. � W/cm�

B. �00 W/cm�

C. � mW/cm�

D. �00 mW/cm�



A87. As the ultrasound wave propagates through

tissue, regions of compression and rarefaction are created. Thus localized regions are sub-jected to increases and decreases in pressure in an alternating fashion, and these cause gas bubbles to exhibit dynamic behavior. This phe-nomenon is known as ________.

A. Radiation forceB. CavitationC. IonizationD. Fourier force

A88. Multiple models have been developed for the

thermal index (TI). These different models are necessary because temperature profiles in tissue are highly dependent on the presence of a strong absorber such as ________.

A. AirB. BoneC. FluidD. All of the above

A89. A number of epidemiologic studies of in utero

ultrasound exposure have been conducted over the past �0 years. What is the conclusion of the NCRP regarding a causal relationship between diagnostic ultrasound and any adverse effect?

A. Low birth weight is an adverse effect caused by in utero ultrasound exposure

B. Dyslexia is an adverse effect caused by in utero ultrasound exposure

C. Delayed speech development is an adverse effect caused by in utero ultrasound expo-sure

D. Insufficient justification to warrant the con-clusion that there is a causal relationship between diagnostic ultrasound and any adverse effect

A90. What is the conclusion of the National Institutes

of Health (NIH) regarding the appropriate use of ultrasound in obstetrics?

A. Routine screening is recommendedB. Ultrasound examination in pregnancy

should be performed for a specific medical indication

C. Ultrasound examination performed solely to satisfy the family’s desire to obtain a picture of the fetus should be encouraged to en-hance bonding between mother and child

D. None of the above

A91. According to recommendations by the NCRP,

a risk-benefit decision should be considered when the mechanical index (MI) exceeds a value of ________ and the thermal index (TI) exceeds a value of ________.

A. �.0, �.0B. 0.�, 0.�C. 0.�, �.0D. �.0, 0.�E. None of the above; the NCRP makes

no recommendations with respect to MIs and TIs

�8 Radiation Biology Syllabus for Diagnostic and Interventional Radiologists�8 2007

Answers


1. A

2. D

3. B

4. C

5. A-True B-False C-False D-False

6. A-True B-True C-True D-True E-True

7. A

8. D

9. C

10. B

11. C

12. E

13. A-True B- True C-True D-True

14. C

15. B

16. �-A �-D �-B �-C

17. A-False B-True C-False D-False E-False

18. A-False B-False C-True D-False E-True


20. D

21. A-True B-True C-False D-True E-False


23. A

24. A

25. C

26. A

27. A

28. �-A �-B �-D �-E �-C

29. �-D �-B �-C �-A

30. A-False B-False C-True D-True

31. A-False B-True C-False D-True

32. A-True B-True C-True D-True

33. A-False B-True C-True D-False

34. A-False B-False C-True D-True E-False

35. �-B �-A �-C


37. A-False B-False C-True D-True E-False

38. A-False B-False C-True D-True

39. A

40. A-False B-False C-False D-True

41. A-False B-True C-True D-True


�920072007 Radiation Biology Syllabus for Diagnostic and Interventional Radiologists



44. A-False B-False C-True D-False

45. B

46. C

47. D

48. �-D �-C �-A �-B

49. A-True B-True C-True D-False E-True

50. A-True B-True C-True D-False E-False

51. C

52. A-True B-True C-True D-False

53. C

54. A-False B-True C-False D-True

55. �-C �-B �-D �-A

56. �-C �-B �-A �-D

57. �-B �-D �-A �-C

58. D

59. A-True B-False C-False D-True

60. A-True B-True C-True D-True E-True F-True G-False H-False

61. D

62. C

63. D

64. B


65. A

66. B

67. A

68. A-False B-True C-True D-True

69. C

70. D

71. B


73. B

74. C

75. C

76. E

77. D

IV.Ultrasound

78. A

79. E

80. C

81. A

82. E

83. D

84. H

85. C

86. A

87. B

88. B

89. D

90. B

91. C


Explanation of Answers


Question1. When x rays are absorbed in biologic material, the photon first interacts with an orbital electron of an atom of the material by the photo- electric, or Compton, process to produce a fast recoil electron. The energy of this electron is lost through interactions with other atoms or molecules to produce biomolecular ions. The ensuing biochemi-cal events may or may not lead to a biologic effect. Protons and spallation products are formed when neutrons are absorbed in tissue. The correct option is A (�, pp 9–��; �, pp �7–��).

Question2. X rays are absorbed in biologic mate-rial to produce a recoil electron, as described in Question �. This electron may interact directly with DNA to cause a strand break, but this is relatively unlikely because DNA constitutes a small proportion of the cell. The cell is mostly water, and the electron may ionize a water molecule close to the DNA. This leads to the chemical production of a free hydroxyl radical (OH•), which diffuses to the DNA and causes a strand break. This accounts for about two-thirds of the biologic damage produced by x rays. The correct option is D (�, p ��).

Question3. Dicentrics and rings are “exchange type aberrations”; in other words, they are formed by the illicit rejoining of two separate chromosome breaks. A dicentric is formed as a consequence of rejoining of breaks in two different chromosomes; a ring forms from the rejoining of breaks in the two arms of the same chromosome. The correct option is B (�, pp ��–��; �, p 8�0).

Question4. Damage to bases may represent a mutation, but it does not kill the cell. Thymine dimers are produced by ultraviolet radiation, not by ionizing radiations. Double-strand breaks are the most important lesions caused by x rays. Some are quickly and correctly repaired. Those that remain unrepaired or that rejoin illicitly to form an aberra-tion may cause cell death. The correct option is C (�, pp �8, ��–�9, ��).

Question5. Lymphocytes from a blood sample can be stimulated to divide, and chromosomal aberra-tions can be scored at the first mitosis. The number of aberrations reflects the average effective total body dose. Option A is therefore true (�, pp ��–�8; �, pp �9–�0). The aberrations scored are of the exchange type, such as dicentrics, which require breaks in two chromosomes, so that the relation to dose is linear-quadratic. Hence, option D is false (�, pp ��–�8). The dose that can be detected de-pends on how many cells are scored, but for practi-cal purposes, �� cGy is the lowest dose that can be detected. Option B is therefore false (�, pp ��–�8; �, pp �9–�0). Lymphocytes are very radiosensitive, die an interphase death, and disappear quickly after a large dose. A few days after exposure to �0 Gy, there would be few lymphocytes in circulation, so the system could not be used to assess dose. In any case, the person would have died a gastrointestinal death before � weeks! Option C is therefore false (�, pp ��9–��0; �, pp �9–�0).

Question6. If a break occurs in two prereplication chromosomes, and pieces of chromatin without centromeres are exchanged, this is a symmetric translocation and is compatible with life (option D). If rejoining occurs so that the two pieces with cen-tromeres join, this represents a dicentric (option E). If the two pieces without centromeres join, this forms an acentric fragment (option A). A small piece of chromatin with a centromere is a centric fragment. What usually happens is that a break occurs on each side of the centromere, and the two “sticky” ends join to form a ring chromosome; in other words, the centric fragment is often a ring (option B). When two breaks occur in the same piece of chromatin, and the piece isolated reverses and rejoins, this is called an inversion (option C). All options are true (�, pp ��–��).

Question7. In most mammalian cells, mitosis itself (M) lasts about a half hour to an hour. The DNA syn-thetic phase (S) has a duration of 6–8 hours in rodent cells and about �� hours in human cells. G� has a duration of a few hours. G� is the phase that is most variable in length; it may last only an hour in cells that are dividing rapidly to repair damaged tissue, or it may be �0 days to � weeks in, for example, the stem cells of resting skin. The correct option is A (�, p �69).


Question8. Cells in mitosis (M) or just before, in the G� phase, are the most radiosensitive, while cells in late S are the most radioresistant. G� cells are intermediate in radiosensitivity. When an asynchro-nous population of cells is exposed to x rays, most surviving cells will be from the most radioresistant moiety of the population, S. The correction option is D (�, pp ��–��).

Question9. In the few humans who have died a gastrointestinal death as a consequence of total body irradiation, it is the small intestine that is most completely denuded. The correct option is C (�, pp ��9–��0; �, p 8��).

Question10. Xeroderma pigmentosum is character-ized by sensitivity to ultraviolet radiation but not to x rays. Bloom syndrome and Fanconi anemia both exhibit genomic instability but are not particularly sensitive to either x rays or ultraviolet radiation. The characteristic of ataxia telangiectasia is sensitivity to x rays but not to ultraviolet radiation. The correct option is B (�, p ��).

Question11. The shoulder of the survival curve (the β component in the α-β formalism) is most pronounced for low linear energy transfer (LET) radiations and minimal for high-LET radiations. For a given particle, the LET goes down as the energy goes up. For a given energy, the LET increases with the mass of the particle. Electrons are by far the lightest of the particles listed; pi mesons are the next lightest, then neutrons, with alpha particles the heaviest. The correct option is C (�, pp ��–��; �, pp 8��–8��).

Question12. The number of free radicals produced is a function of dose and does not depend on dose rate; option A cannot be correct. Ion pairs recombine in fractions of a millisecond, so that is not a factor here; option D is incorrect. The mitotic cycle is length-ened, not shortened, by radiation; option B is incorrect. This leaves options C and E. If the dose rate is very low, cell survival would be dominated by cell division occurring during a prolonged exposure, and option C would be correct. However, for any practical dose rates, the dominant factor in the dose-rate effect is the repair of sublethal damage during a prolonged exposure. The correct option is E (�, pp 7�–7�).

Question13. Stochastic effects are effects for which there is no threshold and for which the severity of the effects does not depend on dose, although the probability that the effects will occur does. Stochastic effects include heritable effects and carcinogenesis, but not cell killing. All biologic effects, stochastic or otherwise, depend on all four factors: dose, LET, dose rate, and type of tissue exposed. All options are correct (�, pp ��–��6, ��9–��6; �, p 8�0).

Question14. A total body dose in the range of 0.7�–�.�� Gy results in nausea in �%–�0% of persons exposed. At higher doses in the range of �.��–�.00 Gy, the prevalence increases to �0%–70%. Above �.� Gy, moderate to severe nausea is ex-pected in �0%–90% of persons exposed. The correct option is C (�, p 8�).

Question15. The lymphocyte count would be decreased by a dose of 0.� Gy. A transient early erythema may be produced by a dose of � Gy, with 6 Gy required for a robust erythema. Temporary epilation occurs after a dose of � Gy and permanent epilation after 7 Gy. A dose of �.� Gy or more is re-quired to produce sterility in the female. The correct option is B (�, pp ��–��).

Question16. Three of the four options in this question relate to death by total body irradiation at differing dose levels. The LD �0/60 refers to the death of �0% of the exposed population in 60 days due to failure of the hematopoietic system. Its value is about �–� Gy. C matches with � (�, p ��7). LD �0/� refers to the dose required to kill humans by denuding the lining of the gastrointestinal tract. Its value is about �0 Gy. B matches with � (�, pp ��9–��0). Only a few examples of death by the cerebrovascular syndrome have ever been seen in humans; death occurs in about �8 hours, and the dose required is about �00 Gy. A matches with � (�, pp ��8–��9). The fourth option involves heredi-tary effects (ie, effects in offspring due to irradiation of parents). The dose required to double the natu-ral or spontaneous mutation rate is about � Gy. D matches with � (�, pp �6�, �66).


Question17. The minimum dose of x rays in an acute exposure likely to produce a vision-impairing cataract is � Gy; option A is false (�, p �8�). Dicen-tric chromosomal aberrations in stimulated human peripheral lymphocytes can be observed at any dose above about 0.�� Gy; option B is true (�, p ��). A transient early erythema may be produced by a dose of about � Gy, and a robust erythema requires 6 Gy; option C is false (�, p �0�). Ataxia is not a likely re-sult of any dose, except perhaps hundreds of grays; option D is false (�, pp ��8–��9). The risk estimate for radiation-induced cancer is 8%/Gy for an acute exposure. A ��% increase would require ��/8 Gy, or �.� Gy; option E is false (�, p ��6).

Question18. Vomiting and other GI symptoms in the majority of individuals exposed require a dose of several grays; option A is false (�, pp ��, ��). Diar-rhea indicates a supralethal dose (ie, a dose in ex-cess of �–� Gy); option B is false (�, p ��). Option C is true because temporary sterility in males occurs after a dose as low as 0.�� Gy (�, p �66). However, permanent sterility in females requires a dose of � Gy or more; option D is false (�, p �66). A decrease in lymphocyte count would be observed at a dose as low as 0.� Gy; option E is true (�, p ��).

Question19. The dose that would kill �0% of a population as the result of failure of the hematopoi-etic system (ie, LD �0/60) is �–� Gy; option A is true (�, p ��7). Seizures are not a feature of any radiation dose short of the central nervous system/cerebro-vascular syndrome, which requires a dose in excess of �00 Gy; option B is false (�, pp ��8–��9). The nadir of the white blood cell count, determined by the lifetime of mature circulating cells, is several weeks following irradiation; option C is false (�, p ��; �, pp �9–�0; �, pp �6, ��). Bone marrow transplants cannot save persons exposed to doses in excess of about �0 Gy, because they will die a gastrointestinal death; option D is false (�, pp ��9–��0).

Question20. Transient erythema is evident in hours, and the main wave of erythema occurs after �0 days. Epilation occurs after about � weeks. Ulceration and depigmentation are late effects due to damage to the dermis. Pain would be secondary to extremely high doses. The correct option is D (�, p �0�; �, pp 8�9–8�0).

Question21. Temporary sterility in males occurs after a dose as low as 0.�� Gy; option A is true (�, pp ��7, �66). Permanent sterility in females oc-curs at doses of �.� Gy or more; option B is true (�, pp ��7, �66). Radiation-induced sterility in males does not affect hormone levels or libido; option C is false (�, pp ��7, �66). Radiation-induced sterility in females results in symptoms similar to those in nor-mal menopause; option D is true (�, p ��7). Because the cells in the male reproductive system involve a hierarchy of cells in a self-renewal system, there is a latent period between irradiation and sterility; option E is false (�, p ��7).

Question22. Mutations produced by radiation are indistinguishable from those that occur spontaneous-ly; option A is false (�, p �66). There is no statistically significant excess of hereditary effects in the children of the Japanese exposed to radiation by the atomic bombs, which indicates that humans are certainly not more sensitive than mice and might be less sensitive; option B is false (�, p �6�). Risk estimates for hereditary effects are based on the “Megamouse” project; option C is true (�, pp �6�–�6�). If � Gy (or � Sv) is required to increase the mutation rate by �00%, 0.�–0.� Gy (or Sv) would be required to increase the mutation rate by �0%–�0%. However, the average background radiation in the United States is only � mSv (ie, 0.00� Sv). Option D is false (�, p �66). The doubling dose is the dose required to double the natural or spontaneous level of mutations. The BEIR committee quoted a range, 0.�–�.� Sv, while UNSCEAR quoted a single figure, � Gy. Option E is true (�, p �66).

Question23. The risk estimate for the hereditary effects of radiation, based on a doubling dose of � Gy, plus an allowance for multifactorial diseases, is estimated by the ICRP to be 0.�%/Sv. (For x rays, sieverts and grays are interchangeable units, since the radiation weighting factor for x rays is unity.) The risk for a hereditary effect from an exposure of 0.� Gy is therefore 0.�/�00 × 0.� = � × �0–�, a risk of � in �0,000. The correct option is A (�, p �66).


Question24. Carcinogenesis by radiation is considered to be a stochastic process (ie, it is an all-or-nothing event). The severity of the response is not dose dependent, although the probability of it occurring is. There is no threshold (ie, there is no dose below which there is no risk). The BEIR V and UNSCEAR committees found that for solid tumors in the Japanese survivors, the excess cancer incidence was a linear function of dose, with no threshold. The leukemia data were best fitted with a linear-quadratic function of dose. The correct option is A (�, pp ��, ��–��).

Question25. The thyroid is most sensitive to induc-tion by radiation of both benign nodules and malig-nant tumors. None of the other tissues shows such an incidence of benign tumors due to x rays. The correct option is C (�, pp ��9–��0; �, pp �8�, �90).

Question26. At the time of the Three Mile Island accident, it was estimated that the number of cancer deaths due to the release of radioactive materials was about 0.�! The closest and correct option is A (6, p ��).

Question27. The excess cancer risk estimated by the UNSCEAR and BEIR V committees was 8%/Sv, based on the data from the Japanese survivors. However, the Japanese survivors experienced an acute exposure. The ICRP uses a dose and dose-rate reduction factor (DDREF) of �, so that the estimate of cancer risk at low doses and low dose rate, applicable to the radiation protection of a working population, is �%/Sv. The correct option is A (�, p ��6).

Question28. An excess incidence of leukemia was observed in patients with ankylosing spondylitis treat-ed with x rays for the relief of pain. A matches with � (�, p ��9). An excess of breast cancer was observed in patients who underwent fluoroscopy many times during the management of tuberculosis, first reported from Canada and later repeated in a New England study. B matches with � (�, p ��0). Thyroid tumors, both benign and malignant, were observed in the inhabitants of the Marshall Islands in the Pacific as a

result of fallout from the testing of nuclear weapons. C matches with � (�, p ��9). An excess of lung cancer is observed in underground miners, including uranium miners, who breathe radon, which concen-trates in the environment of the mine. Radon is a noble gas with a half-life of about � days. It decays to solid radioactive isotopes that stick to particles of dust and are deposited in the bronchi and lungs. These radionuclides emit alpha particles that irradi-ate the bronchial epithelium and may cause lung cancer. D matches with � (�, pp ��0–��). Women employed as dial painters ingested radium by licking their brushes for the application of luminous paint to watches. Bone sarcomas and carcinomas of epithelial cells lining the paranasal sinuses and nasopharynx were observed in this exposed population. E matches with � (�, p �66).

Question29. The prostate has a relatively high natural or spontaneous incidence of cancer in the United States, but a low risk of induction by radiation. D matches with � (�, p 8�8; �, p ��6). Thyroid cancer is relatively rare in the population, but both benign and malignant tumors are induced by radiation, espe-cially in children and young people. B matches with � (�, pp ��9–��0). Breast cancer is relatively common in the U.S. population and is readily induced by radia-tion. C matches with � (�, p ��0). Malignancies in the kidney are rare and do not figure prominently in any of the major populations exposed to radiation. A matches with � (�, p 8�8).

Question30. Radiation-induced abortions after a �-Gy exposure are very likely during weeks 0–� of gestation but are unlikely during weeks 8–��; op-tion A is false (�, pp �68–�80). During weeks 0–�, radiation-induced abortions are likely, but congeni-tal abnormalities are unlikely to occur until weeks �–6; option B is false (�, pp �68–�80). Although not high, the risk of mental retardation may occur during weeks ��–�� (a risk level of about �0%/Sv); option C is true (�, pp �68–�80). The risk of mental retar-dation is as much as �0%/Sv during weeks 8–��. During the period of organogenesis (�–6 weeks of gestation), congenital abnormalities are likely after a dose of � Gy; option D is true (�, pp �68–�80).


Question31. In a general dictionary, stochastic is simply defined as “random.” In radiation protection, it has taken on a special specific meaning and ap-plies to carcinogenesis and hereditary effects. A sto-chastic effect is an all-or-nothing effect. The severity of the effect is not dose related; option A is false (�, pp ��–��6). However, the probability of the ef-fect occurring increases with dose; option B is true (�, pp ��–��6). There is no dose below which the effect cannot occur (ie, there is no threshold); op-tion C is false (�, pp ��–��6). Damage to a small number of cells, even one cell, can cause the effect; option D is true (�, pp ��–��6).

Question32. The total number of excess malig-nancies attributable to radiation at Hiroshima and Nagasaki is about 600; option A is true (�, p ��7). There was an increase in leukemia and many solid tumors, including those of the breast; option B is true (�, p ��0). Exposure in utero led to an increased incidence of reduced head diameter and mental retardation; option C is true (�, p �7�). While there is a trend, there was no statistically significant increase in hereditary (genetic) effects in the first-generation children of persons exposed; option D is true (�, p �6�).

Question33. Risk estimates for radiation-induced cancer are based on studies of exposed popula-tions in which there is a clear dose-related excess of cancer cases. Good examples include the survivors of the atomic bombs in Hiroshima and Nagasaki, as well as the women who underwent fluoroscopy many times during the management of tuberculosis; options B and C are true (�, pp ��7–��8). Patients treated with I-�� show no clear dose-related excess of cancer or leukemia, nor do populations living near nuclear power plants; consequently, neither can be used to obtain risk estimates; options A and D are false (�, pp ��7–��8).

Question34. Latency is the time between irradiation and the appearance of malignancy. For leukemia, the latent period is short, on the order of �–7 years, while for solid tumors the latent period may be as long as �0–�0 years. Option A is false (�, p ��8); option D is true (�, p ��8). Children are more sensi-tive than adults for some malignancies, while for others, there appears to be little difference with age. However, children are certainly not less sensitive than adults; option B is false (�, p ��6). Radiation induces benign as well as malignant tumors (thyroid tumors are the best example); option C is true (�, p 8�0). The ICRP risk estimate for radiation-in-duced cancer in a working population at low dose and dose rate is �%/Gy. A dose of 0.� Gy would re-sult in a cancer incidence of 0.�%, not �0%; option E is false (�, p ��6).

Question35. Animal experiments indicate that ex-posure to radiation during organogenesis leads to a wide spectrum of malformations; B matches with � (�, pp �69–�7�). During preimplantation, radiation appears to have an all-or-nothing effect; either the newly fertilized egg is killed, or it develops normally. Growth retardation and malformations do not result from irradiation at this time. A matches with � (�, pp �69–�7�). There is an increased risk of cancer due to exposure in utero; C matches with � (�, pp �69–�7�).

Question36. Prior to 8 weeks after conception, the fetal thyroid does not take up iodine, so hypothyroidism will not occur in the fetus even from a therapeutic dose; option A is true (�, pp ��8–��9). The total body dose to the conceptus from the administration of �0 mCi is less than 7 rad (70 mGy), which is too low to cause death; option B is false (�, pp ��8–��9). The red marrow dose to the mother from the administra-tion of �0 mCi is about 0.09 Sv. The absorbed dose to maternal organs other than the thyroid is typically not more than 0.�� Sv from a �0-mCi administration. The ICRP risk of all cancers from an acute dose of radiation is about 8%/Sv and for leukemia about �%/Sv; both C and D are false (�, pp ��–��6).


Question37. An accident situation in which injuries are possible justifies the small risks associated with diagnostic x rays; option A is false (7, pp ��–��). A therapeutic abortion would not be justified; option B is false (7, pp ��–��). On the basis of the Japanese survivors’ data, 8–�� weeks is the sensi-tive period for reduced head diameter and mental retardation. The doses are not large enough for this to be very likely, but if a radiation-induced defect oc-curred, it would involve the central nervous system; option C is true (�, pp �77–�78). On the basis of the case-control studies of Stewart et al, even a few radiographs during pregnancy increase the risk of leukemia and childhood cancer; option D is true (�, pp �76–�77). The dose to the fetus would be considerably less than 0.� Gy; option E is false (7, pp ��–��).

Question38. Intrauterine death occurs as a result of irradiation during preimplantation (0–�0 days), and neonatal death (ie, death at or about the time of birth) occurs because of irradiation during or-ganogenesis (�0 days to 6 weeks). Irradiation at �8 weeks is too late for this; options A and B are false (�, pp �69–�7�). The data from persons exposed in utero at Hiroshima and Nagasaki show that irradia-tion to a sufficient dose may produce microcephaly (reduced head diameter) and mental retardation. The most sensitive time interval for these effects was 8–�� weeks. There was a less sensitive interval at ��–�� weeks; option C is true (�, pp �76–�77). The case-control studies of Stewart et al showed that even a few obstetric radiographs could lead to an elevation of risk of leukemia and childhood cancer; option D is true (�, pp �76–�77).

Question39. A multislice CT scan results in a dose to the lens of the eye of less than � cGy. Cerebral angiography can contribute an additional dose of � cGy to the lens of the eye. The minimum dose that will produce a cataract in a single exposure is about � Gy. The correct option is A (�, p �8�).

Question40. In the lens, dividing cells are confined to the equatorial region. Progeny migrate to the pos-terior pole of the lens. Cells damaged by radiation lead to opaque fibers that congregate in the posterior pole; option A is false (�, p �8�). The minimum acute dose to produce a cataract is about � Gy; � Gy over � years will certainly not result in a cataract; option B is false (�, p �8�). Prescription eyeglasses today are almost always plastic and absorb little radiation. Lead glass is required to significantly attenuate x rays; option C is false (�, p 77�). Vision-impairing cataracts take time to develop and are preceded by less-impor-tant opacities; option D is true (�, pp �8�–�8�).

Question41. A stochastic effect is one in which the severity of the effect is independent of the dose and for which there is no threshold. In the case of a cataract, there is a practical threshold of � Gy, and the severity of the cataract increases with the dose; option A is false (�, pp �8�–�8�). The minimum dose, in a single acute exposure, required to result in a cataract is indeed � Gy; option B is true (�, pp �8�–�8�). Cataractogenesis by radiation shows a substantial dose-rate and fractionation ef-fect (ie, a larger dose is required if it is protracted); option C is true (�, pp �8�–�8�). For a given dose, high-LET radiations, such as neutrons and heavy charged particles, are much more effective at induc-ing cataracts; option D is true (�, pp �8�–�8�).

Question42. A dirty bomb is a dispersal device that causes purposeful dissemination of radioactive ma-terial over a wide area without a nuclear detonation. Potential sources of radioactive material for a dirty bomb include naturally occurring radionuclides (eg, radium, uranium, thorium), products of the nuclear fuel cycle, radioisotopes used in medicine, com-ponents of military systems, and radiation sources used in industry. Highly radioactive material such as nuclear fuel rods, cobalt-60 teletherapy sources, and industrial radiography units could deliver significant whole body exposure to those present, resulting in acute radiation syndrome. Contaminated-injured patients are anticipated from an explosive device that releases radioactive material. Patients with large amounts of radioactive contamination pose an exposure hazard to medical personnel. As an act of terrorism, the primary purpose of a dirty bomb is to inflict fear, destroy the sense of well-being, and disrupt community function. All options are true (�, pp 9, �6, �7).



Question43. Système International (SI) units are the gray and the sievert. The gray is the unit of absorbed dose and is defined as � J/kg. The sievert is the unit of equivalent dose, or the product of dose in grays and the radiation weighting factor (Wr). The rad, rem, and curie are the old units, replaced in the SI system by the gray, sievert, and becquerel. Options C and E are true (�, p �9).

Question44. The maximum permissible doses recommended by the NCRP are effective doses. Also, the dose outside the lead apron does not reflect the dose under the lead apron. The dose under the lead apron is usually lower by about a factor of �0. The dose to the conceptus is more than a factor of two less than this because of protection from the mother’s overlying tissues. Therefore, the actual dose to the conceptus is less than about 0.� mSv for the 90-day period. This is less than 0.0� mSv to the conceptus per month, which is much lower than the 0.�-mSv monthly limit recommended by the NCRP; option C is true. Option A is false for two reasons: (a) The dose to the conceptus is not at a level of true concern, and (b) the Nuclear Regulatory Commission (NRC) regulates exposures only to radionuclear by-product material. The NRC would be an improper agency to notify for exposures to x rays. The individual can continue to work in fluoroscopy as long as she main-tains proper radiation management practices; option B is false. Since the radiation levels are well below any of concern, option D would be unconscionable (�, p �77; 8; 9, p �8).

Question45. Inhaled radon contributes a little more than half of the effective dose to the U.S. population, with the remainder approximately equally divided between medical radiation and background radiation arising from cosmic rays and from the ground. The correct option is B (�0, p ��).

Question46. Radon is the largest single contributor to the “effective” dose; the effective dose is the prod-uct of the absorbed dose, the radiation weighting factor (Wr), and the tissue weighting factor (Wt ). The radiation weighting factor for the alpha particles emit-ted by radon progeny is �0, while the tissue weighting factor for the lung, the only tissue irradiated by radon progeny, is 0.�. The correct option is C (�0, p ��).

Question47. Medical (including dental) radiation represents about a quarter of the effective dose to the U.S. population and is therefore by far the larg-est source of exposure from human activity. Natural background radiation is slightly greater. The correct option is D (�0, p ��).

Question48. The effective dose from average background radiation, including radon, for the United States is about � mSv per year; D matches with � (�0, p ��). Once a pregnancy is declared, the NCRP dose limit to the conceptus is 0.� mSv per month. Until a pregnancy is declared, there are no special dose limits other than those applicable to any radia-tion worker. C matches with � (9, p �8). The effective dose received in flying across the North Atlantic in a commercial jetliner is about 0.0� mSv. This is due to the cosmic radiation at the altitude of about ��,000 feet. A matches with � (�0, p ��). The genetically significant dose (GSD) is the dose that if given to everyone in the U.S. population would result in the same number of mutations as would the actual vari-able dose received by part of the population during medical irradiation. The GSD is about 0.�� mSv. B matches with � (�0, p ��).

Question49. Radon tends to accumulate in the basement of a house as it seeps in from rocks and soil. This is particularly true in winter when the house is heated and the pressure inside is a little less than that outside. This draws radon into the house. In the outside air, radon dissipates. Option A is true. The BEIR VI best estimate of lung cancer deaths from radon was ��,�00 to ��,800 per year, depending on which model is adopted. This is about �0% of the lung cancer deaths per year, which were about ��7,990 in �00� in the United States. Option B is true. Two of the progeny of radon emit energetic alpha particles, which are thought to be the cause of lung cancer; option C is true. When radon decays into solid progeny, it does so with a half-life of about � days; option D is false. The parent is indeed radium; option E is true (�, pp �89–�90).


Question50. Radon is a naturally occurring radioactive gas that seeps out of the ground into mines and the basements of homes; option A is true. Radon constitutes about ��% of the effective dose to the U.S. population, which is about double that from medical x rays; option B is true. In the United States, the action level for radon (the maximum concentration in the lived-in area of a house above which modifica-tions to the building are recommended) is � pCi/L. This is lower than the action levels in Canada and Europe. Option C is true. The half-life of radon is about � days; it is radium that has a half-life of about �,600 years; option D is false. Two of the progeny of radon emit energetic alpha particles, which are thought to cause lung cancer; option E is false (�, pp �89–�90).

Question51. Of the options given, fluoroscopy of the trunk of the body involves by far the largest dose to the operator. The correct option is C (�, pp ��–��, 7��, 769–770).

Question52. The genetically significant dose (GSD) is the dose that if given to everyone in the U.S. popu-lation would result in the same number of mutations as would the actual variable dose received by part of the population during medical irradiation. The GSD due to medical radiations, therefore, depends on the gonad doses, the age and sex of the patients, and the number of persons exposed; options A, B, and C are true. The time of day is obviously irrelevant; op-tion D is false (�, p 7�6; �0, p �).

Question53. Until a worker declares a pregnancy, no special protection limits apply apart from those generally applicable to a radiation worker. Once a pregnancy is declared, the recommended limit is 0.� mSv per month. If this is adhered to, the dose for the duration of the pregnancy would be similar to that allowed for an occasional exposure of a member of the general public. The mother may be a radiation worker, but the conceptus is not. The correct option is C (9, p �8).

Questions54. Hands and legs are of concern for deterministic effects, which do not include cancer induction; option A is false (�, p ��). The risk of cancer from low-dose-rate exposures is about �%/Sv; option B is true (�; p ��6). Hands are allowed a larger maximum dose (�00 mSv) than the eyes (��0 mSv) because the eyes are much more sensitive to radiation;

option C is false (�, p ��). Because of repair of dam-age, a low-dose-rate exposure is less effective than a high-dose-rate exposure; option D is true (�, p ��6).

Question55. The genetically significant dose is the dose that if given to everyone in the U.S. population would result in the same number of mutations as would the actual variable dose received by part of the population during medical irradiation. It therefore gives some idea of the impact of gonadal radiation. C matches with � (�0, p �). Dose is a physical term, expressed as energy per unit mass. One gray of different types of radiation does not result in the same biologic effect. The equivalent dose is the product of dose and the radiation weighting factor (Wr), a dimen-sionless factor designed to reduce all radiation to a common scale. The unit is the sievert. One sievert of any kind of radiation produces the same biologic effect. B matches with � (9, p �6). Different organs and tissues show different susceptibilities to the biologic effects of radiation. The effective dose is the sum of the products of equivalent dose and the tissue weighting factor (Wt ) for all organs or tissues exposed. D matches with � (9, p ��). In the case of an incorpo-rated radionuclide, the dose is not delivered instan-taneously but over a period of time depending on the half-life of the radionuclide. Committed equivalent dose takes that into account and is the effective dose integrated over �0 years. A matches with � (9, p ��).

Question56. The maximum permissible effective dose for individuals occupationally exposed is �0 mSv per year; C matches with � (9, p ��). The public is allowed an exposure that is one-tenth of the occupational cumulative dose limit of �0 mSv per year; B matches with � (9, p �6). After a pregnancy is declared, the maximum permissible dose per month to the conceptus is 0.� mSv, so that during the duration of the pregnancy the dose is similar to that allowed a member of the general public as an occasional exposure (one-tenth of the annual occupational effective dose limit); A matches with � (9, p �8). The limit for the eye of an occupationally exposed individual is ��0 mSv, which is designed to prevent a deterministic effect; D matches with � (9, p �6).

Question57. The unit of absorbed dose is the gray, defined as � J/kg; B matches with � (9, p �9). The unit of activity of a radionuclide is the becquerel, defined


as one disintegration per second; D matches with � (9, p �9). The equivalent dose is the product of absorbed dose in grays and the radiation weighting factor (Wr), which is a dimensionless factor. The unit is the sievert. A matches with � (9, p 60). The collective effective dose is the sum of the effective doses for all members of a population. The unit is the person- sievert. C matches with � (�, p �96; �, p 7��).

Question58. The maximum permissible dose for the hands is �00 mSv because the main concern for the hands is not skin cancer but deterministic effects. Maximum permissible dose is based on low-dose-rate exposures, and nuclear power plant employees have not contributed to the database for hand expo-sure. The correct option is D (�, p ��).

Question59. The minimum age for occupationally exposed workers is �8 years; option A is true (9, p ��). It is assumed that medical radiation confers some benefit, so it is not included in the dose al-lowed to a person occupationally exposed; option B is false (9, p ��). ALARA is intended to minimize oc-cupational exposure; option C is false (9, p ��). The purpose of radiation protection for those occupation-ally exposed is to prevent deterministic effects and limit stochastic effects to levels that are acceptable against a background of other risks in society; option D is true (9, p 9).

Question60. The patient attenuates a fraction of the incident x rays. This fractional reduction in x-ray intensity is essentially independent of the patient’s position between the x-ray source and image recep-tor. Therefore, the automatic brightness control response is also independent of patient position. Changing the source-to-skin distance from �0 inches to �� inches can increase the entrance exposure rate by a factor of �.8. Option A is true (�, p 778). Many modern fluoroscopy systems have the capabil-ity to freeze the last image on the monitor after the x-ray exposure is terminated. This allows the physi-cian to study the last image and plan the next task without radiation exposure to the patient. Option B is true (�, p 778; ��, pp ��–��9). During pulsed fluoroscopy, the x-ray beam is emitted as a series of short pulses rather than continuously. For continu-ous fluoroscopy, the video display is a constant �0 frames per second. At reduced frame rates, sub-stantial dose reduction can be achieved. Images can be acquired at �� frames per second rather than

the usual �0 frames per second. Dose reduction is �0%. However, manufacturers may increase the radiation level per frame to achieve a more pleasing visual appearance, and the dose reduction may be only ��%. Nevertheless, pulsed fluoroscopy offers reduced exposure rate and improved image quality compared with continuous fluoroscopy (sampling time for each frame is less with pulsed fluoroscopy). Pulsed fluoroscopy can be performed at lower frame rates (�0, 7.�, or � frames per second). Low frame rates adversely affect the ability to display rapidly moving structures. Option C is true (�, p 778; ��, pp ��–��9). The design of the fluoroscopy system may incorporate operator-selectable filtration. Substan-tial reductions in skin dose, particularly for large patients, can be achieved by inserting appropriate metal filters (aluminum, copper, or other materi-als) into the x-ray beam at the collimator. Filtration reduces skin dose by preferentially removing low-energy x rays, which generally do not penetrate the patient to contribute to the image. Option D is true (��, pp ��–��9). The presence of a grid improves contrast by absorbing scattered x rays. However, the dose to the patient is increased by a factor of two or more. For pediatric cases, the removal of the grid reduces the dose, with little degradation of image quality. Grids should be used with discretion when fluoroscopic studies are performed on children. These systems should have the capability for easy removal and reintroduction of the grid. Option E is true (��, pp ��–��9). In most interventional fluoro-scopic procedures, the x-ray beam is directed toward a particular anatomic region for the bulk of the fluoroscopic time. Some reduction in maximum skin dose can be achieved by periodically rotating the fluoroscope to image the anatomy of interest from a different direction. This method tends to spread the entry dose over a broader area, thereby reducing the maximum skin dose. Option F is true (��, p �70). A magnified image (reduced field of view) typically results in higher dose to the patient. There are two ways to magnify the image: geometric and electronic. The geometric method usually positions the patient closer to the x-ray source but can also be achieved by moving the image receptor farther away from the patient. The technique factors are driven higher for electronic magnification because a smaller area of the image receptor is utilized for image formation. Each method increases the entrance exposure rate. Options G and H are false (�, p ��7).


Question61. The use of protective clothing (aprons and thyroid collars) in addition to ceiling-mounted lead glass shields is well documented (�, p 77�). The transmission of x rays through radiation-attenuat-ing surgical gloves is typically stated as 60%–70% at 80 kVp. In clinical practice, this value is higher (less attenuating) because of beam geometry differ-ences. By comparison, devices made with 0.�-mm lead-equivalent material have a transmission of �%. Radiation-attenuating surgical gloves offer minimal protection of the operator’s hands. The instanta-neous dose from scatter radiation is reduced some-what when the hands covered with one layer of glove material are located near the radiation field. Howev-er, the total time near the radiation field depends on the speed at which the procedure is performed, as well as the distance from the imaged anatomy when the x-ray beam is activated. The increased thickness of these gloves reduces dexterity and therefore can increase procedure time. The automatic brightness control system in fluoroscopy increases the radia-tion output to penetrate the glove when the hand is present in the beam. This can be confirmed by noting that anatomy is seen even though the glove is present. The dose to the hand is comparable to that when the radiation-attenuating glove is not present.

The following statements are from “Teaching Radiation Safety to Invasive Fluoroscopists” by S. Balter, PhD (��):

Radiation-attenuating surgical gloves are available. They offer minimal protection to the operator’s hands. (There is a real myth around that these gloves elimi-nate hand exposure.) The automatic exposure control system often increases radiation output to “penetrate” the gloves. Anatomy is seen through �, �, or 6 layers of glove material. The operator’s hand is covered by a single layer of glove material.

The cost of radiation-attenuating surgical gloves and the minimal dose reduction do not justify the use of these devices in a risk-versus-benefit radiation protection analysis. Radiation-attenuating surgical gloves provide a false sense of protection and are not recommended. The correct option is D (��, p �7�).

Question62. On September �0, �99�, the FDA issued a Public Health Advisory regarding radiation-induced skin injuries from fluoroscopic procedures. These injuries are usually delayed, so the physician cannot discern damage by observing the patient immediately after the treatment. The radiation dose required to cause skin injury is typically � Gy for erythema (onset �–� days after exposure) and tem-porary epilation (onset �–� weeks after exposure). Additional fluoroscopy time above the threshold dose increases the severity of the skin injury: a dose of 6 Gy for main erythema (onset �0 days after exposure) and a dose of ��–�0 Gy for moist desquamation (onset � weeks after exposure). Vascular damage is expected for skin doses above �0 Gy. The proce-dures of concern are primarily interventional pro-cedures during which fluoroscopy is used to guide instruments. The dose rate to the skin from the direct beam is typically between � and � rad/min (�0–�0 mGy/min) for continuous fluoroscopy. The maximum exposure rate permitted by the FDA is �0 R/min. The dose rate is usually reduced if pulsed fluoroscopy is employed. For units with a high-level fluoroscopy mode of operation, the maximum exposure rate to the skin from the direct beam is �0 R/min. Risk of skin injury is associated with prolonged fluoroscopy time. The time required to deliver a threshold dose for temporary epilation is typically greater than �.� hours in fluoroscopy (0.0� Gy/min). At maximum exposure rate, the time to deliver this dose to a single skin site is �0 minutes in normal mode and �� minutes in high-level fluoroscopy mode. Large patients are more susceptible to skin injury because automatic brightness control automatically changes (without operator intervention) the technique factors to increase the x-ray output. The correct option is C (�, p �0�; �, p 8�0; ��, p �).


Question63. Since ultrasound is nonionizing radia-tion, no radiation dose is delivered to the fetus (�, p ��). Scattered radiation to the fetus from a head CT examination is less than 0.0� mGy (�, pp 80�–80�). The entrance exposure for a KUB radiograph is usually about �00 mR. By using a dose conversion factor of 0.� rad/R for the fetus (depends on beam quality, patient size, and field size), the dose per radiograph is estimated to be 60 mrad (0.6 mGy). The chest radiographic examination is a very low-dose procedure requiring only an entrance exposure of �0–�0 mR (0.�–0.� mGy) for the posteroanterior projection and slightly more for the lateral projection (�, p 798). Scattered radiation to the fetus would be considerably lower. The correct option is D (�, p 798; 6, p ��).

Question64. For a declared pregnancy, the dose limit to the fetus is �00 mrem (� mSv). For fluoros-copy, portable radiography, and nuclear medicine imaging, the dose to the conceptus from occupational exposure to the mother will very likely be less than � mSv if proper radiation protection practices are followed. Radioiodine treatments with I-�� sodium iodide are considered to place the fetus at higher probability of exceeding � mSv and are potentially very hazardous in terms of uncontrolled release of the radioactive material. The fetal thyroid takes up radioiodine after age �� weeks. The correct option is B (8, pp �9–��).


Question65. Actively shielded magnets are designed to decrease the surrounding fringe field so that siting concerns are reduced. Nevertheless, a strong mag-netic field is present in the magnet room. Ferromag-netic materials (oxygen tanks, hemostats, scissors, etc) brought into the magnet room can become airborne as projectiles in the static magnetic field. Projectiles pose a serious risk to the patient and others in the magnet room. Patient screening and staff training are the most effective methods to exclude ferromagnetic materials from the magnet room. However, new ferromagnetic detection systems are capable of detecting small ferromagnetic objects external to the patient and can now differentiate between ferromagnetic and nonferromagnetic mate-rials. The ACR recommends ferromagnetic detection systems as an adjunct to screening of patients and devices. The correct option is A (��, p �).

Question66. Pregnant health care workers have not been shown to be at increased risk of adverse outcomes from exposure to static magnetic fields. Although pregnant health care practitioners are per-mitted to work in the MR environment, they should not remain within the magnet room during data acquisition/imaging. The recommendation to exit the MR magnet room during data acquisition/imaging is not based on reported studies of potential adverse effects but is a conservative approach based on a recognition that there are insufficient data regarding the effects of MR electromagnetic fields. Positioning patients, imaging, archiving, injection of contrast agent, and entering the MR magnet room in response to an emergency are considered acceptable activities for the pregnant health care worker. The correct option is B (��, p 9; ��, pp �78–�79).

Question67. On the basis of the currently available data, there is no association of cancer or any other deleterious effect with the use of clinical MR imaging during pregnancy. The ACR has adopted the policy that MR procedures may be performed during any stage of pregnancy if medically indicated. The use of ultrasound, the desired information and effect on the management of the patient, and the potential for delay are appropriate considerations for the selec-tion of a pregnant patient for MR imaging. The MR procedure is considered appropriate if the informa-tion requested addresses the clinical problem or is necessary to manage potential complications for the patient and/or fetus; that is, the results of the MR examination can potentially affect the care of the patient and/or fetus during the pregnancy. The risk to the fetus from gadolinium-based contrast agents is unknown and may be harmful. MR contrast agents should not be routinely administered to pregnant patients. The ACR makes no recommendation regarding appropriate pulse sequences or imaging parameters. The correct option is A (��, p 9).


Question68. The vast majority of patients with NSF were receiving therapy with dialysis or had stage � or � renal disease at the time of MR imaging with gadolinium-based contrast agents. The population at risk can be identified by an additional question regarding a history of renal disease or dialysis. Prospective hematologic screening is not warranted. Option A is false. No special treatment is recom-mended for patients with stage � or � chronic kidney disease (defined as GFR > 90 mL/min/�.7� m� or GFR between 60 and 89 mL/min/�.7� m� ). However, gadodiamide (Omniscan) is not recommended for a patient with any level of renal disease. Option B is true. A risk-benefit assessment for that particular patient with stage �, �, or � renal disease should in-dicate a clear benefit for the administration of a gad-olinium-based contrast agent. The default standard dose for these patients should be one-half the usual dose. A written order from the radiologist approving the examination is recommended. Informed consent should also be provided. Under these conditions, option C is true. If patients with severe to end-stage renal disease receive gadolinium-based contrast agents, prompt dialysis following MR imaging should be considered. Option D is true (��, p 9).

Question69. All implanted intracranial aneurysm clips composed of titanium and/or titanium alloy are acceptable for MR imaging without any additional testing. However, documentation of the composition in writing is necessary. The correct option is C (��, pp �, ��, �6).

Question70. Quenching is the loss of superconduc-tivity of the magnet coils, which is accompanied by the rapid escape of helium as evidenced by clouds or fog around the MR imager. Helium will displace oxygen in the room. All magnet rooms should have helium-venting equipment. The ACR, citing reliability concerns, does not currently recommend oxygen monitors in the magnet room. An uncontrolled quench is an emergency situation requiring the rapid removal of all personnel/patients from the magnet room. Site access must be restricted until the magnetic field has dissipated. The correct option is D (��, pp ��–��).

Question71. The need for controlled access is based on the potential risk from the attraction of objects containing ferromagnetic materials, torque on metallic materials, and the possible dysfunction of medical implants for persons with such devices inadvertently entering the area. Control may be established by barriers or signs based on the manufacturer’s recom-mendations. The correct option is B (�6, p �7).

Question72. Significant risk criteria were developed by the FDA to include static magnetic field over � T, RF exposure sufficient to produce a core temperature increase of �°C, time-varying magnetic fields (dB/dt) sufficient to produce severe discomfort or painful stimulation, and peak acoustic noise over ��0 dB. All options are true (�6, p 6).

Question73. During MR imaging, the patient absorbs a portion of the transmitted RF energy, which results in tissue heating. This could cause an elevation of core body temperature or a skin burn by localized heating. The specific absorption ratio (SAR) is the dosimetric means by which RF power absorbed per unit mass is characterized. The FDA has set limits for SARs to limit whole-body and local temperature rise. The SAR should not exceed � W/kg for the whole body for �� minutes, � W/kg averaged over the head for �0 minutes, 8.0 W/kg in � g of tissue (head or torso) for �� minutes, and �� W/kg in � g of tissue (extremities) for � minutes. Alternatively, RF heat-ing is considered acceptable if the core temperature increase is less than �°C and local heating is no greater than �8°C in the head, �9°C in the trunk, and �0°C in the extremities. The SAR is proportional to the number of images acquired per unit of time and depends on patient dimensions, RF waveform, tip angle, and coil type. Patient heating also depends on ambient temperature, relative humidity, airflow rate, blood flow, and patient insulation. The correct option is B (�, pp �6�–�67; ��, p �6; �6, p 6).

Question74. Gradient magnetic fields are rapidly applied by passing currents through the gradient coils. In the presence of the static magnetic field, a current in the gradient coil creates a force on the coil, which causes the coil to vibrate. The mountings for coils also flex and vibrate in response to move-ment of the gradient coils. The result is acoustic noise in the form of loud knocking. The correct option is C (��, p ��9).


Question75. Rapidly switched gradients allow improved image quality and faster acquisition. The potential physiologic response includes peripheral nerve stimulation, muscle movement, and discomfort. The thresholds for cardiac stimulation and brain stim-ulation are much greater than for peripheral nerve stimulation and are unlikely to occur with current MR systems. The correct option is C (��, pp ��–��).

Question76. Focal heating and thermal injuries have been induced by time-varying RF magnetic fields during MR examination. The presence of a conductive loop (crossed arms, ECG leads or un-connected surface coil leads in contact with patient’s skin, etc) can produce induced electrical currents, which can cause thermal injury. Near the inner bore of the magnet, high levels of RF standing waves may form. The patient must be positioned so that there is no direct contact between the patient’s skin and the inner bore of the magnet. Absorption of RF energy by the metallic object creates a heated surface, which can cause local temperature elevations. The correct option is E (��, pp �0–��; �7).

Question77. At magnetic field strengths below � T, no deleterious biologic effects (either acute or chronic) have been identified. At magnetic field strengths above � T, magnetophosphenes and vertigo have been reported. The two major concerns associated with the static magnetic field are forces exerted on ferromagnetic objects (either rotational or attractive) and magnetically sensitive equipment whose func-tion may be disrupted. The correct option is D (�, pp �6�–�67; �7).

IV.Ultrasound

Question78. The instantaneous intensity (i) is determined from the measured acoustic pressure (p) by using the equation,

i =p2

,ρc

where c is the speed of sound, and ρ is the density of the medium. Intensity parameters, such as (a) spatial peak, temporal average intensity and (b) spatial average, temporal average intensity, are typically derived by averaging the instantaneous intensity with respect to space, time, or both. Frequently, pulsed-wave ultrasound is characterized by a peak negative pressure (expressed in megapascals). The peak negative pressure is also called the peak rarefac-tional pressure. The correct option is A (�8, p �96).

Question79. Relative measurement of intensity compares the value at one point with a reference intensity and is expressed on a logarithmic scale in units of decibels (dB). The intensity change or level in decibels is

Level (dB) = 10 log I , Iref

where I is the intensity at the point of interest, and I ref is the reference intensity. If the intensity at the point of interest equals one-half the reference intensity, then the level in decibels calculated by �0 log (0.�) is –� dB. The correct option is E (�8, p ��).

Question80. The “Standard for Real-time Display of Thermal and Mechanical Acoustic Output Indices on Diagnostic Ultrasound Equipment” was adopted by the AIUM and NEMA in �99�, with minor revisions in �996 and �998. This benchmark, which has become known as the output display standard (ODS), devel-oped a formalism to calculate in real time the effect of operator-selected parameters on acoustic output. Two acoustic output parameters, the thermal index (TI) and the mechanical index (MI), were devised. The TI, in essence, gives the maximum temperature rise in tissue caused by energy absorption, and the MI describes the likelihood of cavitation based on peak rarefactional pressure and frequency. The cor-rect option is C (�9).


Question81. The thermal index indicates the maximum temperature rise in tissue based on a homogeneous tissue model and instrument param-eters (power, transducer aperture, beam dimen-sions, and scanning mode). The correct option is A (�8, pp ��0–��).

Question82. The heat production rate in a small volume is determined by the absorption coefficient of the tissue and the time-averaged intensity of the ultrasound beam, which depends on the pulse rep-etition frequency and power. The rate of absorption for most tissues increases linearly with frequency. Variations in the heat production rate occur because of different tissue types and nonuniformity of the ultrasound field. The initial rate of temperature rise cannot be maintained. Heat removal by conduction and perfusion quickly slows the rate of temperature rise. Focused beams create small localized regions of heating. The removal of heat from small volumes is very rapid. Continuous insonation ultimately produces a steady-state condition in which the maximum temperature does not change. Results of experiments quantifying the heating of rat skull bone exposed to a focused ultrasound beam form the basis for thermal models involving the insonation of bone. The correct option is E (�8, p ��8).

Question83. Thermal-induced damage is a thresh-old phenomenon; that is, no biologic effects are observed unless the temperature elevation exceeds a particular value for a minimum time duration. For example, a temperature increase of �.�°C must be present for � hours to cause fetal abnormalities. At higher temperatures, the time necessary to induce damage is shortened dramatically (eg, at ��°C, the time decreases to � minute). The correct option is D (�0, p ��).

Question84. Time-gain compensation (TGC) and gray-scale mapping do not affect acoustic output. TGC is a processing technique during acquisition which applies variable amplification to the detected signal based on time delay since the transmitted pulse. Gray-scale mapping is a postprocessing technique which translates echo signal strength into brightness level in the displayed image. The correct option is H (�8, pp ��–�67, �9�–�97).

Question85. Cavitation is more likely to occur at high pressures and low frequencies. Scientific re-search has indicated that cavitation-induced effects may be possible at peak pressures and frequencies within the operational range of diagnostic equipment. Specifically, lung and intestinal hemorrhages in mice have been reported at diagnostic output levels. The mechanical index equals the peak rarefactional pressure in tissue divided by the square root of the frequency and is expressed as a dimensionless quantity. For water, cavitation has not been observed if the mechanical index is less than 0.7 over the frequency range �–�0 MHz. The correct option is C (�8, p ��6).

Question86. The Bioeffects Committee of the AIUM was established to examine the current knowledge concerning bioeffects and to assess the risk of clini-cal diagnostic ultrasound. This committee regularly publishes critiques of research reports and issues statements regarding the safety of diagnostic ultra-sound. Its conclusions are acknowledged to be safety guidelines throughout the ultrasound com-munity. The history and rationale for this statement are provided in Bioeffects and Safety of Diagnostic Ultrasound (��). The correct option is A (��).

Question87. Cavitation can be either stable or transient. In stable cavitation, microbubbles already present in the medium expand and contract dur-ing each cycle in response to the applied pressure oscillations. The bubbles may also grow as dissolved gas leaves the solution during the negative-pressure phase, a process called rectified diffusion. Each bub-ble oscillates about the expanding radius for many cycles without collapsing completely. At a character-istic frequency (which is a function of the size of the bubble), the vibration amplitude of neighboring liquid particles is maximized. Transient cavitation is a more violent form of microbubble dynamics in which short-lived bubbles undergo large size changes over a few acoustic cycles before completely collapsing. During the rarefaction phase, bubbles may be formed by dissolved gases leaving the solution, or bubbles of submicron dimensions may already exist in the medium. The correct option is B (�8, p �0�).


Question88. Three thermal indices corresponding to soft tissue (TIS), bone (TIB), and cranial bone (TIC) have been developed depending on whether bone is encountered along the path and, if it is, whether bone is located near the transducer or in the interior of the body. TIS applies when the ultrasound beam passes through soft tissue only and bone is not present (examinations of the abdomen and fetus during the first trimester). If bone is encountered near the transducer, then TIC is used (examina-tions of pediatric and adult head). TIB applies if the ultrasound beam, after passing through soft tissue, impinges on bone near the focal zone (examinations of the fetus during the second and third trimesters). The correct option is B (�8, p ��0).

Question89. Epidemiologic studies and surveys of clinical experience have yielded no firm evidence of any adverse effects from in utero ultrasound exposure. An association of diagnostic ultrasound with low birth weight, dyslexia, and delayed speech development has been reported in some studies. However, the majority of epidemiologic studies have been negative for any bioeffect. The correct option is D (��, pp ��–��7).

Question90. Based on bioeffects data and clinical efficacy, as well as psychosocial, economic, and legal/ethical issues, the NIH panel concluded that ultrasound examination in pregnancy should be performed for a specific medical indication. A recom-mendation for routine screening was not justified by data on clinical efficacy and safety. Specifically, there is not enough evidence that routine screening benefits either the mother or the fetus. There is no evidence showing potential damage to either mother or fetus from routine screening. The correct option is B (��, pp �–��).

Question91. The acoustic pressure or temperature rise at the site of interest may be either under- estimated or overestimated by the acoustic output parameter, and therefore the knowledgeable user must consider the nature of the clinical situation in order to make an informed judgment. The NCRP recommends the risk-benefit decision if the MI exceeds 0.� or the TI exceeds �.0. The correct option is C (��, p ��).

��2007 Radiation Biology Syllabus for Diagnostic and Interventional Radiologists

�. Hall EJ, Giaccia AJ. Radiobiology for the radiologist. 6th ed. Philadelphia, Pa: Lippincott Williams & Wilkins, �006.

�. Bushberg JT, Siebert JA, Leidholdt EM, Boone JM. The essential physics of medical imaging. �nd ed. Philadelphia, Pa: Lippincott Williams & Wilkins, �00�.

�. American College of Radiology. Disaster preparedness for radiology professionals: response to radiological terrorism— a primer for radiologists, radiation oncologists, and medical physicists. Reston, Va: American College of Radiology, �00�.

�. Military Medical Operations. Medical management of radiologi-cal casualties handbook. �nd ed. Armed Forces Radiobiology Research Institute Web site. http://www.afrri.usuhs.mil/www/outreach/pdf/�edmmrchandbook.pdf. Published April �00�. Accessed April ��, �007.

�. Committee on the Biological Effects of Ionizing Radiation. Health effects of exposure to low levels of ionizing radiation. Washington, DC: National Academy of Sciences, National Research Council, �990.

6. Hendee WR, Ritenour ER. Medical imaging physics. �th ed. New York, NY: Wiley-Liss, �00�.

7. National Council on Radiation Protection and Measurements. Medical radiation exposure of pregnant and potentially pregnant women. NCRP report no. ��. Bethesda, Md: National Council on Radiation Protection and Measurements, �977.

8. Hedrick WR, Feltes JJ, Starchman DE, Berry GC. Managing the pregnant radiation worker: a realistic policy for hospitals today. Radiol Manage �986:8(�):�8–��.

9. National Council on Radiation Protection and Measurements. Limitations of exposure to ionizing radiation. NCRP report no. ��6. Bethesda, Md: National Council on Radiation Protection and Measurements, �99�.

�0. National Council on Radiation Protection and Measurements. Ionizing radiation exposure of the population of the United States. NCRP report no. 9�. Bethesda, Md: National Council on Radiation Protection and Measurements, �987.

��. Hernanz-Schulman M, Emmons MA, Price RR. Fluoroscopy clinical practice: controlling dose and study quality—new challenges and opportunities. In: Frush DP, Huda W, eds. �006 Syllabus: categorical course in diagnostic radiology physics—from invisible to visible: the science and practice of x-ray imaging and radiation dose optimization. Oak Brook, Ill: Radiological Society of North America, �006; ��–��9.

��. Balter S. Teaching radiation safety to invasive fluoroscopists. In: Frey GD, Sprawls P, eds. The expanding role of medical physics in diagnostic imaging: proceedings of the �997 summer school. American Association of Physicists in Medicine monograph no. ��. Madison, Wis: Medical Physics Publishing, �997.

��. Center for Devices and Radiological Health. FDA Public Health Advisory: avoidance of serious x-ray-induced skin injuries to patients during fluoroscopically-guided procedures. Rockville, Md: Food and Drug Administration, �99�.

��. Kanal E, Barkovich AJ, Bell C, et al. ACR guidance document for safe MR practices: �007. AJR Am J Roentgenol (in press). American College of Radiology Web site. http://www.acr.org/s_acr/bin.asp?TrackID=&SID=�&DID=��8��&CID=��60&VID=�&DOC=File.PDF. Accessed May �, �007.

��. Shellock FG, ed. Magnetic resonance procedures: health effects and safety. Boca Raton, Fla: CRC Press, �00�.

�6. Computed Imaging Devices Branch, Office of Device Evaluation, Center for Devices and Radiologic Health. Guidance for the submission of premarket notifications for magnetic resonance diagnostic devices: guidance for industry. Food and Drug Ad-ministration Web site. http://www.fda.gov/cdrh/ode/mri��0.pdf. Updated November ��, �998. Accessed April ��, �007.

�7. Kanal E, Shellock FG, Talagala L. Safety considerations in MR imaging. Radiology �990;�76(�):�9�–606.

�8. Hedrick WR, Hykes DL, Starchman DE. Ultrasound physics and instrumentation. �th ed. St Louis, Mo: Elsevier Mosby, �00�.

�9. American Institute of Ultrasound in Medicine and National Electrical Manufacturers Association. Standard for real-time display of thermal and mechanical indices on diagnostic ultrasound equipment. Rockville, Md: American Institute of Ultrasound in Medicine and National Electrical Manufacturers Association, �99�.

�0. National Council on Radiation Protection and Measurements. Exposure criteria for medical diagnostic ultrasound. I. Criteria based on thermal mechanisms. NCRP report no. ��. Bethesda, Md: National Council on Radiation Protection and Measurements, �99�.

��. American Institute of Ultrasound in Medicine. Bioeffects and safety of diagnostic ultrasound. Laurel, Md: American Institute of Ultrasound in Medicine, �99�.

��. National Council on Radiation Protection and Measurements. Exposure criteria for medical diagnostic ultrasound. II. Criteria based on all known mechanisms. NCRP report no. ��0. Bethesda, Md: National Council on Radiation Protection and Measurements, �00�.

��. U.S. Department of Health and Human Services. Diagnostic ultrasound imaging in pregnancy. NIH publication no. 8�-667. Bethesda, Md: National Institutes of Health, �98�.

References

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