emergency radiology

1

Emergency Radiology:The Basics

Rathachai Kaewlai, MDSpecialized in Body Imaging and Emergency Radiology

[email protected] 2006

The author is willing to receive any input, comments and corrections, Please do not hesitate to contact at the above email address.

2

Study Objectives

• After studying, the readers should be knowledgeableof– Basic physics of different imaging modality, especially plain

radiography, US and CT.– Advantages and limitations of each modality.– Basic rules in requesting radiology examinations.– Basic principle of picture archiving communication systems

(PACS).– Current and future trends in radiology.

3

Basics: Plain Film Radiography

• Plain film radiography uses x-ray as a source tocreate an image on the screen, and projected as ahard-copy image or into a computer.

• It is a 2D image of a 3D object (human organs), thisshould be kept in mind and there is extensiveoverlapping structures in plain film radiographs. Thisissue is resolved by…– Do at least 2 views perpendicular to each other; for

example, chest x-ray in PA and lateral views.– Do a cross-sectional imaging such as CT, MRI or

ultrasound to overcome the overlapping.

4

Basics: Plain Film Radiography

• There are 5 relative different radiodensities inmedical x-ray. This is presented from the least denseto the most dense particles (Dark to bright)

Density Appearance– Air least dark– Fat less dark, but still dark– Soft tissue medium– Bone bright– Metal most brightest

5

Basics: Plain Film Radiograph

• Projections (views) ofradiograph determined by– Location of the x-ray tube and the

x-ray film in relation to thepatient’s anatomy.

• For example, Postero-anterior(PA) view means the x-ray beamtravels from front to back of thepatients and hit the film in theback of the patients. Chest x-ray (PA)

6

Chest x-rays of the same patientperformed in the same day, in twodifferent projections (above; PA,below; AP).

The difference between PA and AP,is the organ (or part of the body) thatis closer to the film, will be bettervisualized. For example, in PA skullradiograph, the lesion in frontal bonewill be better visualized than inoccipital bone. In chest radiograph,different magnification causes thecardiac silhouette to be larger in APprojection. The rule is ‘put the film onthe side of interest’.

7


• Projections (views) of radiograph determined by– Position of the patient: this will define the heaviness of

movable substances in our body. Air goes up against thegravity, free fluid follows the gravity.

• Right/left decubitus: Right lateral decubitus is putting the rightside of the patient down. This is still a frontal (AP or PA)radiograph.

• Lateral cross-table: A lateral projection that is taken across theside of the patient when he/she is on the bed.

8


• Portable radiograph:– The only indication is when the patient is “too sick to leave

the bed”. Example - ICU patients, injured patients on thetrauma board or in the operating rooms.

• Cons: Different magnification (distortion of the size of organs),decreased quality of the images.

• Usually it is done in AP projection, which is still different fromAP projection performed in the radiography room.

9


• Stress radiograph:– Put a stress (either

patient’s own weight, forceor extra weights to carry)on specific organs, usuallyjoints. For example,acromioclavicular jointsradiograph, standing kneeradiograph,flexion/extension views ofthe cervical spine.

10

Basics: Computed Tomography

• There is no superimposition in CT.• CT gives more information on different tissue density.• CT works by

– Passing a thin x-ray beam through the body of the patient inthe axial plane, as the x-ray tube moves in a continuous arcaround the patient.

– The opposite side of the x-ray tube are electronic detectors.The detectors converted the exit beam into electronicsignals.

– The signals are sent to the computer, which calculates the x-ray absorption values and arrange the image.

11


• Hounsfield unit (HU) = the absorption value of x-raybeam in the tissue.– Water is assigned the value of zero.– Approximate HU for fluid 0-20 HU, acute blood 40-60 HU.– Denser value (white) ranges upward to bone, and metal.– Less dense value (darker) ranges downward through fat to

air.– The picture is produced equivalent to a radiograph of that

cross-sectional slice of the patient.

12


• CT ‘window’– Different windowing in CT allows optimal evaluation of

each organs; e.g. subdural window (for subdural blood),brain window (for brain parenchyma), bone window (forbone), etc.

13


• CT protocol– Almost all CT scans were performed in axial plane. These

axial scans can be processed into sagittal, coronalreformations or others.

– What is useful to find out, as a clinician?• Scanner type (conventional, helical, multidetector),• Slice thickness (ranges from submillimeter

to 10 mm),• Location of first and last slices (to see the extent of study;

will it include the organ of interest?),• Type of contrast usage (what kind of contrast will radiologists

give to the patients?)

14


• View the CT scan as though youwere looking up at it from thepatient’s feet.

• CT protocol– Different radiology departments

have different CT protocols. It isbest to know your own hospital’sradiology department scannersand protocols, in order to adjustit with your own practice.

RightLeft

15


• Reformatted CT images– The CT scanner computer or a

separate computer can stack a seriesof CT slices on top of one another, sothe stack can be sliced in other planessuch as coronal, sagittal or obliqueplanes.

– The techniques are especially useful tosee pathology of the spine, long bone,joint. Coronal images are easier tounderstand by clinicians.

Reformatted CT images and 3DCT can be performed with multidetector CT scanners.

16


• Three-dimensional CT (3DCT)– As explained in previous page,

computer can also stack multipleslices into 3D image of the softtissues, bones or blood vessels.

– Useful to provide a surgeon withthe most realistic display of thepathology; especially complexorthopedic injuries.

Reformatted CT images and 3DCT can be performed with multidetector CT scanners.

17

Basics: CT Angiography

• Scanning when the IV contrast bolus reaches itspeak in the vascular structures being studied (eitherarterial or venous).

• Similarity with conventional angiography– Give same information in a much less invasive way.– Use of x-ray and IV contrast material.

18


• Technical difference from CT– Need faster scanner (helical, multidetector).– Need faster IV contrast injection rate (means

larger size of the needle).

• Technical difference from conventionalangiography– No placement of angiographic catheter (non-

invasive).– Unable to provide treatment such as

angioplasty, stent placement, etc.

19


• Head-to-toe applications– Head and neck: aneurysm, AVM,

carotid atherosclerosis, venous sinusthrombosis, etc.

– Body: aortic dissection, pulmonaryembolism, coronary artery, renalartery stenosis, deep veinthrombosis, etc.

– Extremity: brachial, femoralarteriogram.

• Preparation– No oral contrast or rectal contrast

used.

20

Basics: MRI

• MRI uses very powerful magnets, ranging from 0.3 to3 Tesla (in clinical practice).

• The patient is placed in the magnet bore, radio wavesare passed through the body in particular sequences.The body tissues respond by emitting the pulses,which are then recorded by a detector, sent tocomputer.

21

Basics: MRI

• Various body tissues emitcharacteristic MR signals, whichdetermine whether they will appearwhite, gray or black on the images.

• In general: Water is black on T1-WI (T1 weighted image), white onT2-WI. Most tumors andinflammatory masses appear whiteon T2-WI. Compact bone appearsblack in all sequences. T1-WI

T2-WI

22

Basics: MRI

• Advantages– Greater differentiation of soft tissue

structures.– Can be acquired in any planes.– Can provide vascular study without use of

IV contrast.

• Disadvantages– Longer time of scanning.– Motion artifacts from respiration, cardiac

pulsation (for scanning of the chest andabdomen).

T1-WI

T1-WI + IV contrast

23

Basics: Ultrasound

• Use of high-frequency sound waves and its reflectionto create the cross-sectional images of the body.

• Advantages– No ionizing radiation, no biological injury.– Can be acquired in any planes.– Less expensive machine and exam cost.– Can be performed at the bedside of the very sick patients.– Provide moving images of the heart, fetus, and other

structures.

24

Basics: Ultrasound

• Disadvantages– Less sharp and clear images,– Take more time than CT,– Quality and accuracy

depending on operator’sskills.

– Some structures such asbone and lung cannot beexamined. Normal Doppler US of the

lower extremity veins

25

Basics: PACS

• Picture Archiving Communication Systems (PACS) arecomputers or networks dedicated to the storage, retrieval,distribution and presentation of images.

• It replaces hard-copy medical images (such as plain filmradiographs, ultrasound, CT and MRI). Radiologists use PACSto see the images and interpret them.

• Advantages:– Image manipulation: brightness, contrast, rotate, zoom,

measurements, etc. Better diagnostic accuracy, e.g. see throughbone in chest x-ray.

– Less storage space for hard-copy images, less risky for wrongpatient’s identification.

– Teleradiology.

26

With PACS, radiologists can ‘play’with the images in multiple way. Forexample: we can look at lung, ribsand spine in one chest radiographwithout difficulty.

27

Prepare Your Patients for Imaging

• Rule #1: select the right imaging technique to answerthe specific clinical question.– Know the indications.– Know what to expect from each imaging modality (its

limitation and usefulness).– Know your hospital capability (scanners, radiologist’s

preference and ability).

• Rule #2: check the contraindication.• Rule #3: discuss with the radiologist(s).• Rule #4: prepare the patients.

28

Rule #1

• The American College of Radiology (ACR) has published‘Appropriateness Criteria’ for imaging investigation in variousclinical settings in its website,http://www.acr.org/s_acr/sec.asp?CID=1845&DID=16050 forseveral years.

• This criteria has been proposed to be used by referringphysicians for a better and efficient way of choosing theright imaging modality to answer the specific clinicalquestion.

• They will be presented separately in the upcoming lectures ineach topic.

29

Rule #2

• CT: contraindications– There is no absolute contraindication if benefits weigh

risks.– X-ray related: in pregnant patients and children– Contrast related:

• Hypersensitivity to iodinated contrast medium.• History of seafood allergy is NOT a contraindication to

iodinated contrast medium administration. Although, if otherallergic disorders coexist, this will increase the chance ofhaving contrast hypersensitivity.

• Asthma, allergic disorders increase risk of hypersensitivity.• Renal failure, diabetes, current use of metformin contribute to

increased risk of contrast-related renal failure.

30

Rule #2

• CT: contraindications - What To Do?– Pregnancy, children Other modalities (MRI, US)– Risk of hypersensitivity Premedication with oral/IV

steroids (consult your radiologist)Use non-ionic contrast medium reduces the risk of minor reaction.

– High serum creatinine Usually defined as Cr > 1.5 inhealthy adults, lower in older individuals.Treatment protocol varies (consult your nephrologist)

31

Rule #2

• MRI: contraindications– Generally, MRI is very safe and adverse reactions to

contrast agents are extremely rare.– Absolute contraindications

• Cardiac pacemakers,implanted cardiac defibrillators, otic/innerear/cochlear implants, metal fragments in the eye.

– Others• Heart valve, aneurysm clip (depending on the models), passive

implants (depending on its ferromagnetic status).• Pregnancy: No known risks, however, late effects on fetus

may be unrealized since MR has been widely available for only15 years. Gadolinium is not FDA-approved during pregnancy.

32

Rule #3

• Know your radiologist– Communication is the key. Two-way communication

between clinicians and radiologists is encouraged for abetter patient care.

– Having radiologists in the emergency department will makea difference.

• There is a different nature of ‘emergency radiology’ from otherradiology subspecialties.

– Safe, fast, effective radiology protocols– Supervision of the technical performance of imaging. Performing

bedside procedures.– Timely interpretation of the images.– Better communication with the emergency physicians.

33

Rule #4

• Prepare the patients– Plain film radiography and CT

• All sexually-active women must be checked for potentialpregnancy.

• If IV contrast will be used:– Serum creatinine is mandatory in patients of old age, history of

kidney disease, diabetes, hypertension.– History of previous hypersensitivity reaction or allergy disease. For

diabetics, metformin use need to be checked.• If oral contrast will be used:

– If bowel perforation is suspected; use water-soluble contrast.• If rectal contrast will be used:

– If bowel perforation is suspected; use water-soluble contrast.

34

Rule #4

• Prepare the patients– Ultrasound

• Depending on the type of exams: fasting, full bladder may beneeded.

• Make sure there is no obstructing object at the area of interest(such as bandage).

– MRI• Complete MRI request checklist.• There might be a need for sedation in children and

claustrophobic patients.

35

What to Expect

• Increased volume of patients through the emergencydepartment.

• Increased volume of radiologic procedures in theemergency department.

• Increased use of advanced imaging technique fornoninvasive diagnosis and treatment.

• Modern ED incorporates emergency radiology(plain film radiography, ultrasound and CT) as asubsection. The ultra-modern ED will have MRI.

36

Current Trends in ED Radiology

• Total body CT scan for multiply injured patient:Scanning from head down to pelvis in one pass,allowing rapid and accurate diagnosis of multipleorgan injuries ranging from brain, chest,abdomen/pelvis, spine from cervical down tothoracolumbar region.

• Stroke protocol: optimized protocol for rapid strokediagnosis, diagnosis of ‘salvageable’ brain forpotential anticoagulation treatment or interventions.

• Cervical spine CT for trauma: More accurate andfaster than plain film radiography.

37

Current Trends in ED Radiology

• Chest CT to rule out PE: Historically difficultdiagnosis becomes easier in seconds of MDCTscanning.

• Stone protocol abdomen CT: More accurate thanplain film radiograph, faster than IVP and mostimportantly, MDCT detects alternative diagnosis suchas appendicitis, gynecologic conditions, etc.

• Bone CT with 3D reformation for complexfractures: Help in orthopedic treatment planningsuch as fractures of the acetabulum, tibial plateau.

38

New Trends in Radiology

• CT colonography (Virtual colonoscopy)• CT bronchography (Virtual bronchoscopy)• Coronary calcium scoring• Coronary CT angiography• Fusion PET-CT (Positron emission tomography-

computed tomograph)• Functional MRI• Molecular imaging

39

How Radiology Effects Patient Care

• Pros– Help in clinical decision making, ‘surgical VS. medical’ issue.– Triage patients toward proper areas (discharge, observation

unit, surgery or admission).– Fast, accurate, noninvasive diagnosis.– This could lead to faster treatment, better outcome and an

overall better patient care.

• Cons– Higher cost?– Non-important incidental findings from CT may lead to

multiple unnecessary follow ups.

40

• Suggested reading:– Basics in radiology

• Novelline RA. Squire’s Fundamentals of Radiology, 6th edition(2004).

– American College of Radiology Appropriateness Criteria• http://www.acr.org/s_acr/sec.asp?CID=1845&DID=16050

41

• The information provided in this presentation…– Does not represent the official statements or views of the

Thai Association of Emergency Medicine.– Is intended to be used as educational purposes only.– Is designed to assist emergency practitioners in providing

appropriate radiologic care for patients.– Is flexible and not intended, nor should they be used to

establish a legal standard of care.

emergency radiology

Health & Medicine

plain film

reformatted

multidetector

computed tomography

ap projection

emergency

emergency

iv contrast