ct basics 2

Neuroradiology

Dr. Grant J. Linnell

Fellow

Montreal Neurological Hospital

McGill University

CT Basics

• Neuroradiology• The BASICS of CT

– CT History– Protocol– Terminology– Contrast– Radiation Safety– Cases

CT Basics

• No disclosures

Neuroradiologist

• A consultant in imaging and disease of the brain, spinal cord, head, neck, face and peripheral nerves

Neuroradiology

• Plain Film• CT• US• MRI• Interventional

– Angiography– Myelography– Biopsy

• Nuclear Medicine

Neuroradiology

• A request for an exam is a consultation– History– Pertinent physical exam findings

• Lab results– Creatinine

– PT/INR

– What is the question?

CT Basics

• Computed tomography (CT)

• Computed axial tomography or computer –assisted tomography (CAT)

CT Basics

CT History

• Electro-Musical Instruments

CT History

SIR GODFREY N. HOUNSFIELD • 1979 Nobel Laureate

in Medicine

CT History

• 1972 – First clinical CT scanner– Used for head examinations– Water bath required– 80 x 80 matrix– 4 minutes per revolution– 1 image per revolution– 8 levels of grey– Overnight image reconstruction

CT History

• 2004 – 64 slice scanner– 1024 x 1024 matrix– 0.33s per revolution– 64 images per revolution– 0.4mm slice thickness– 20 images reconstructed/second

CT Basics



CT Protocolling

• What happens when an exam is requested?– A requisiton is completed.

– The requested exam is protocolled according to history, physical exam and previous exams.

– The patient information is confirmed.

– The exam is then performed.

– Images are ready to be interpreted in …• Uncomplicated exam – 5-10 minutes after completion

• Complicated exams with reconstructions take at least 1 hour but usually 1-2 hours.

CT Protocolling• CT head protocols

– With or Without contrast– CT Brain– CT Brain with posterior fossa images– CT Angiogram/Venogram – CT Perfusion– CT of Sinuses– CT of Orbit– CT of Temporal bones– CT of Mastoid bones– CT of Skull– CT of Face

CT Protocolling

• Variables– Plain or contrast enhanced– Slice positioning– Slice thickness– Slice orientation– Slice spacing and overlap– Timing of imaging and contrast administration– Reconstruction algorhithm– Radiation dosimetry

CT Protocolling

• Patient Information– Is the patient pregnant?

• Radiation safety

– Can the patient cooperate for the exam?

CT Basics

• Neuroradiology

• The BASICS of CT– CT History– Protocol– Terminology– Contrast– Radiation Safety– Cases (Stroke)

CT Terminology

• Exams using Ionizing radiation – Plain film– CT

• 1/10 of all exams• 2/3 OF RADIATION EXPOSURE

– Fluoroscopy• Angiography, barium studies

– Nuclear medicine• V/Q scan, bone scan

CT Terminology

• Attenuation– Hyperattenuating (hyperdense)– Hypoattenuating (hypodense)– Isoattenuating (isodense)

• Attenuation is measured in Hounsfield units– Scale -1000 to 1000

• -1000 is air

• 0 is water

• 1000 is cortical bone

CT Terminology

• What we can see– The brain is grey

• White matter is usually dark grey (40)

• Grey matter is usually light grey (45)

• CSF is black (0)

• Things that are brite on CT– Bone or calcification (>300)

– Contrast

– Hemorrhage (Acute ~ 70)

– Hypercellular masses

– Metallic foreign bodies

CT Terminology

• Voxel– Volume element

• A voxel is the 2 dimensional representation of a 3 dimensional pixel (picture element).

– Partial volume averaging

CT Terminology

CT Terminology

• Window Width– Number of Hounsfield units from black to

white

• Level or Center– Hounsfield unit approximating mid-gray

CT Terminology

CT Artifacts

CT Terminology

• Digital reading stations are the standard of care in interpretation of CT and MRI.

• Why?– Volume of images– Ability to manipulate and reconstruct images– Cost

CT Terminology

• DICOM– Digital Imaging and Communications in

Medicine– DICOM provides standardized formats for

images, a common information model, application service definitions, and protocols for communication.

CT Basics



Contrast

• Barium

• Iodinated – vascular– Biliary, Urinary– CSF

• Gadolinium

Contrast

Contrast

• Types of iodinated contrast– Ionic – Nonionic - standard of care

• No change in death rate from reaction but number of reactions is decreased by factor of 4.

• If an enhanced study is needed, patient needs to be NPO at least 4 hours and have no contraindication to contrast, ie allergy or renal insufficiency.

Contrast• What are the risks of iodinated contrast?

– Contrast reaction• 1 in 10,000 have true anaphylactic reaction• 1 in 100,000 to 1 in 1,000,000 will die

– Medical Issues• Acute renal failure• Lactic acidosis in diabetics

» If on Glucophage, patient must stop Glucophage for 48 hours after exam to prevent serious lactic acidosis

• Cardiac

– Extravasation

Contrast

• Who is at risk for an anaphylactic reaction?– Patients with a prior history of contrast reaction– Patients with a history asthma react at a rate of

1 in 2,000– Patients with multiple environmental allergies,

ie foods, hay fever, medications

Amin MM, et al. Ionic and nonionic contrast media: Current status and controversies.

Appl Radiol 1993; 22: 41-54.

Contrast

• Pretreatment for anaphylaxis– 50 mg Oral Prednisone 13, 7 and 1 hour prior

to exam– 50 mg oral Benedryl 1 hour prior to exam– In emergency, 200 mg iv hydrocortisone 2-4

hours prior to exam

Contrast

• What are the risk factors for contrast induced acute renal failure?– Pre-existing renal insufficiency– Contrast volume– Dehydration– Advanced age– Drugs– Multiple myeloma– Cardiac failure

Contrast

• Considerations in patients with renal insufficiency– Is the exam necessary?– Is there an alternative exam that can answer the

question?– Decrease contrast dose

Contrast

• Pretreatment for renal insufficiency– Hydration– Mucomyst

• 600 mg po BID the day before and day of study

Prevention of radiographic-contrast-agent-induced reductions in renal function by acetylcysteine.

Tepel M, et al. N Engl J Med 2000 Jul 20;343(3):180-4

Contrast

• Contrast induced renal failure– Elevated creatinine 24-48 hours after contrast

which resolves over 7-21 days.– Can require dialysis

Mehran, R. et al. Radiocontrast induced renal failure:Allocations and outcomes.

Reviews in Cardiovascular Medicine Vol. 2 Supp. 1 2001

CT Basics



Radiation Safety

• Diagnostic CT Scans: Assessment of Patient, Physician, and Radiologist Awareness of Radiation Dose and Possible Risks– Lee, C. et al. Radiology 2004;231:393

Radiation Safety

• Deterministic Effects– Have a threshold below which no effect will be

seen.

• Stochastic Effects– Have no threshold and the effects are based on

the dose x quality factor.

Radiation Safety

• Terminology– Gy = Gray is the absorbed dose (SI unit)

• The equivalent of 1 joule/kg of tissue

• Rad = radiation absorbed dose

– Sv = Sievert is the dose equivalent (SI unit)• Absorbed dose multiplied by a quality factor

• Rem = radiation equivalent man

Radiation Safety

• Relative values of CT exam exposure– Background radiation is 3 mSv/year

• Water, food, air, solar

• In Denver (altitude 5280 ft.) 10 mSv/year

– CXR = 0.1 mSv– CT head = 2 mSv– CT Chest = 8 mSv– CT Abdomen and Pelvis = 20 mSv

-The equivalent of 200 CXR

Radiation Safety

• Effects of X rays.– Absorption of photons by biological material

leads to breakage of chemical bonds.– The principal biological effect results from

damage to DNA caused by either the direct or indirect action of radiation.

Radiation Safety• Tissue/Organ radiosensitivity

– Fetal cells– Lymphoid and hematopoietic tissues;

intestinal epithelium– Epidermal, esophageal, oropharyngeal

epithelia– Interstitial connective tissue, fine vasculature– Renal, hepatic, and pancreatic tissue– Muscle and neuronal tissue

Radiation Safety

• Estimated Risks of Radiation-Induced Fatal Cancer from Pediatric CT – David J. Brenner, et al. AJR 2001; 176:289-296

• Additional 170 cancer deaths for each year of head CT in the US.

– 140,000 total cancer deaths, therefore ~ 0.12% increase

– 1 in 1500 will die from radiologically induced cancer

Radiation Safety

• 3094 men received radiation for hemangioma– Those receiving >100 mGy– Decreased high school attendance– Lower cognitive test scores

Per Hall, et al. Effect of low doses of ionising radiation in infancy on cognitive function in adulthood: Swedish population based cohort studyBMJ, Jan 2004; 328: 19 - 0.

Radiation Safety

• Hiroshima and Nagasaki– There has been no detectable increase in

genetic defects related to radiation in a large sample (80,000) of survivor offspring, including: congenital abnormalities, mortality (including childhood cancers), chromosome aberrations, or mutations in biochemically identifiable genes.

William J Schull, Effects of Atomic Radiation: A Half-Century of Studies from Hiroshima and Nagasaki, 1995.

Radiation Safety

• Hiroshima and Nagasaki– However, exposed individuals who survived

the acute effects were later found to suffer increased incidence of cancer of essentially all organs.

William J Schull, Effects of Atomic Radiation: A Half-Century of Studies from Hiroshima and Nagasaki, 1995.

Radiation Safety

• Hiroshima and Nagasaki– Most victims with high doses died– Victims with low doses despite their large

numbers are still statistically insignificant.

Radiation Safety

Comparison of Image Quality Between Conventional and Low-Dose Nonenhanced Head CT

Mark E. Mullinsa, et al.

AJNR April 2004.

Reduction of mAs from 170 to 90

Radiation Safety

• What does all this mean?– 1 CXR approximates the same risk as:

• 1 year watching TV (CRT)

• 1 coast to coast airplane flight

• 3 puffs on a cigarette

• 2 days living in Denver

– 1 Head CT is approximately 20 CXR

Health Physics Society on the web--http://hps.org

Radiation Safety

• The pregnant patient– Can another exam answer the question?– What is the gestational age?– Counsel the patient

• 3% of all deliveries have some type of spontaneous abnormality

• The mother’s health is the primary concern.

Radiation Safety

• "No single diagnostic procedure results in a radiation dose that threatens the well-being of the developing embryo and fetus." -- American College of Radiology

• "Women should be counseled that x-ray exposure from a single diagnostic procedure does not result in harmful fetal effects. Specifically, exposure to less than 5 rad has not been associated with an increase in fetal anomalies or pregnancy loss." -- American College of Obstetricians and Gynecologists

Conclusion

• Neuroradiologists are consultants• Garbage in ------- Garbage out• CT Terminology

– Attenuation (density) in Hounsfield units– Digital interpretation is standard of care

• CT has risks– Contrast– Radiation exposure

CT Basics

• Neuroradiology

• The BASICS of CT– CT History– Protocol– Terminology– Contrast– Radiation Safety– Cases

Normal CT

1 day 1 year 2 years

Normal CTOlder person

Normal Enhanced CT

Case 1

• 55 yo female with sudden onset of worst headache of life

Case 1

Case 1

• What do I do now?

Normal Angiography

Diagnostic Angiography

Case 1

• Subarachnoid Hemorrhage– Most common cause is trauma– Aneurysm– Vascular malformation– Tumor– Meningitis– Generally a younger age group

Case 2

• 82 yo male with mental status change after a fall

Case 2

Case 2

• Subdural hematoma

• Venous bleeding from bridging veins

• General presentation– Older age group– Mental status change after fall– 50% have no trauma history

Subdural Hematoma

Case 3

• 44 yo female with right sided weakness and inability to speak

Case 3

Case 3

• Acute ischemic left MCA stroke

MCA Stroke“Dense MCA”

Case 4

• 50 yo male post head trauma.

• Pt was initially conscious but now 3 hours post trauma has had a sudden decrease in his neurological function.

Case 4

Case 4

• Epidural hematoma– Typical history is a patient with head trauma

who has a period of lucidity after trauma but then deteriorates rapidly.

– Hemorrhage is a result of a tear through a meningeal artery.

Case 5

• 71 yo male who initially complained of incoordination of his left hand and subsequently collapsed

Case 5

Case 5

• Intraparenchymal hemorrhage– Hypertensive– Amyloid angiopathy– Tumor– Trauma

Case 6

• 62 yo female acute onset headache– Hemiplegic on the right and unable to speak

Case 6

• Add htn image here

Case 6

• Hypertensive hemorrhage– Clinically looks like a large MCA stroke– Generally younger than amyloid angiopathy

patients

Chronic Ischemic change =Encephalomalacia

Thrombolysis:

• Intravenous– 3 hours

• Intra-arterial – 6 hours ICA territory– 24 hours basilar territory

• CT head plain shows no established stroke nor hemorrhage

• CT perfusion shows a salvagable penumbra

Case 7

• 53 y.o. male

• Sudden onset of ataxia loss of consciousness proceeding rapidly to coma

Case 7

• Probable basilar occlusion with cerebellar and brainstem infarction

Case 8

• 52 yo male with right sided weakness

Case 8

Case 8

• Acute lacunar infarction– Cannot reliably differentiate this finding on CT

from remote lacune without clinical correlation.

– MRI with diffusion is the GOLD STANDARD– A word on TIA

Chronic Small Vessel Disease

Case 9

• 59 yo female with multiple falls over last weekend

Case 9

Case 9

• Stroke involving caudate head, anterior limb internal capsule and anterior putamen.

• What is the artery?

• Recurrent artery of Heubner

Case 10

• 42 yo male found in coma

Case 10

Case 10

• Global ischemia

Angiographic Brain Death

Case 11

• 24 yo male with siezures

Case 11

Case 11

• Heterotopia

Case 12

• 34 y.o. female

• Severe H/A,nausea

• Taking oral contraceptives

Case 12

Case 12

• Transverse sinus thrombosis

ct basics 2

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