Rathachai Kaewlai

1. Emergency Radiology:
The Basics
Rathachai Kaewlai, MD
Specialized in Body Imaging and Emergency Radiology
rathachai@gmail.com
November 2006
The author is willing to receive any input, comments and corrections,
Please do not hesitate to contact at the above email address. 1

2. Study Objectives
• After studying, the readers should be knowledgeable
of
– 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.
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3. Basics: Plain Film Radiography
• Plain film radiography uses x-ray as a source to
create an image on the screen, and projected as a
hard-copy image or into a computer.
• It is a 2D image of a 3D object (human organs), this
should be kept in mind and there is extensive
overlapping structures in plain film radiographs. This
issue 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.
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4. Basics: Plain Film Radiography
• There are 5 relative different radiodensities in
medical x-ray. This is presented from the least dense
to 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
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5. Basics: Plain Film Radiograph
• Projections (views) of
radiograph determined by
– Location of the x-ray tube and the
x-ray film in relation to the
patient’s anatomy.
• For example, Postero-anterior
(PA) view means the x-ray beam
travels from front to back of the
patients and hit the film in the
back of the patients. Chest x-ray (PA)
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6. The difference between PA and AP,
is the organ (or part of the body) that
is closer to the film, will be better
visualized. For example, in PA skull
radiograph, the lesion in frontal bone
will be better visualized than in
occipital bone. In chest radiograph,
different magnification causes the
cardiac silhouette to be larger in AP
projection. The rule is ‘put the film on
the side of interest’.
Chest x-rays of the same patient
performed in the same day, in two
different projections (above; PA,
below; AP).
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7. Basics: Plain Film Radiograph
• 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 the
gravity, free fluid follows the gravity.
• Right/left decubitus: Right lateral decubitus is putting the right
side of the patient down. This is still a frontal (AP or PA)
radiograph.
• Lateral cross-table: A lateral projection that is taken across the
side of the patient when he/she is on the bed.
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8. Basics: Plain Film Radiograph
• Portable radiograph:
– The only indication is when the patient is “too sick to leave
the bed”. Example - ICU patients, injured patients on the
trauma 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 from
AP projection performed in the radiography room.
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9. Basics: Plain Film Radiograph
• Stress radiograph:
– Put a stress (either
patient’s own weight, force
or extra weights to carry)
on specific organs, usually
joints. For example,
acromioclavicular joints
radiograph, standing knee
radiograph,
flexion/extension views of
the cervical spine.
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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 in
the axial plane, as the x-ray tube moves in a continuous arc
around the patient.
– The opposite side of the x-ray tube are electronic detectors.
The detectors converted the exit beam into electronic
signals.
– The signals are sent to the computer, which calculates the x-
ray absorption values and arrange the image.
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11. Basics: Computed Tomography
• Hounsfield unit (HU) = the absorption value of x-ray
beam 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.
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12. Basics: Computed Tomography
• 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 (for
bone), etc.
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13. Basics: Computed Tomography
• CT protocol
– Almost all CT scans were performed in axial plane. These
axial scans can be processed into sagittal, coronal
reformations 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?)
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14. Basics: Computed Tomography
• View the CT scan as though you
were looking up at it from the
patient’s feet.
• CT protocol
– Different radiology departments
have different CT protocols. It is
best to know your own hospital’s
radiology department scanners
and protocols, in order to adjust Right
it with your own practice. Left
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15. Basics: Computed Tomography
• Reformatted CT images
– The CT scanner computer or a
separate computer can stack a series
of CT slices on top of one another, so
the stack can be sliced in other planes
such as coronal, sagittal or oblique
planes.
– The techniques are especially useful to
see pathology of the spine, long bone,
joint. Coronal images are easier to
understand by clinicians.
Reformatted CT images and 3DCT can be performed with multidetector CT scanners. 15

16. Basics: Computed Tomography
• Three-dimensional CT (3DCT)
– As explained in previous page,
computer can also stack multiple
slices into 3D image of the soft
tissues, bones or blood vessels.
– Useful to provide a surgeon with
the most realistic display of the
pathology; especially complex
orthopedic injuries.
Reformatted CT images and 3DCT can be performed with multidetector CT scanners. 16

17. Basics: CT Angiography
• Scanning when the IV contrast bolus reaches its
peak in the vascular structures being studied (either
arterial or venous).
• Similarity with conventional angiography
– Give same information in a much less invasive way.
– Use of x-ray and IV contrast material.
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18. Basics: CT Angiography
• Technical difference from CT
– Need faster scanner (helical, multidetector).
– Need faster IV contrast injection rate (means
larger size of the needle).
• Technical difference from conventional
angiography
– No placement of angiographic catheter (non-
invasive).
– Unable to provide treatment such as
angioplasty, stent placement, etc.
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19. Basics: CT Angiography
• Head-to-toe applications
– Head and neck: aneurysm, AVM,
carotid atherosclerosis, venous sinus
thrombosis, etc.
– Body: aortic dissection, pulmonary
embolism, coronary artery, renal
artery stenosis, deep vein
thrombosis, etc.
– Extremity: brachial, femoral
arteriogram.
• Preparation
– No oral contrast or rectal contrast
used.
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20. Basics: MRI
• MRI uses very powerful magnets, ranging from 0.3 to
3 Tesla (in clinical practice).
• The patient is placed in the magnet bore, radio waves
are passed through the body in particular sequences.
The body tissues respond by emitting the pulses,
which are then recorded by a detector, sent to
computer.
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21. Basics: MRI
• Various body tissues emit
characteristic MR signals, which
determine whether they will appear
white, gray or black on the images. T2-WI
• In general: Water is black on T1-
WI (T1 weighted image), white on
T2-WI. Most tumors and
inflammatory masses appear white
on T2-WI. Compact bone appears
black in all sequences. T1-WI
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22. Basics: MRI
T1-WI
• 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 and
abdomen).
T1-WI + IV contrast
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23. Basics: Ultrasound
• Use of high-frequency sound waves and its reflection
to 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.
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24. Basics: Ultrasound
• Disadvantages
– Less sharp and clear images,
– Take more time than CT,
– Quality and accuracy
depending on operator’s
skills.
– Some structures such as
bone and lung cannot be
Normal Doppler US of the
examined.
lower extremity veins
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25. Basics: PACS
• Picture Archiving Communication Systems (PACS) are
computers or networks dedicated to the storage, retrieval,
distribution and presentation of images.
• It replaces hard-copy medical images (such as plain film
radiographs, ultrasound, CT and MRI). Radiologists use PACS
to see the images and interpret them.
• Advantages:
– Image manipulation: brightness, contrast, rotate, zoom,
measurements, etc. Better diagnostic accuracy, e.g. see through
bone in chest x-ray.
– Less storage space for hard-copy images, less risky for wrong
patient’s identification.
– Teleradiology.
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26. With PACS, radiologists can ‘play’
with the images in multiple way. For
example: we can look at lung, ribs
and spine in one chest radiograph
without difficulty.
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27. Prepare Your Patients for Imaging
• Rule #1: select the right imaging technique to answer
the 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.
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28. Rule #1
• The American College of Radiology (ACR) has published
‘Appropriateness Criteria’ for imaging investigation in various
clinical settings in its website,
http://www.acr.org/s_acr/sec.asp?CID=1845&DID=16050 for
several years.
• This criteria has been proposed to be used by referring
physicians for a better and efficient way of choosing the
right imaging modality to answer the specific clinical
question.
• They will be presented separately in the upcoming lectures in
each topic.
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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 other
allergic disorders coexist, this will increase the chance of
having 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.
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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 in
healthy adults, lower in older
individuals.
Treatment protocol varies
(consult your nephrologist)
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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/inner
ear/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 only
15 years. Gadolinium is not FDA-approved during pregnancy.
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32. Rule #3
• Know your radiologist
– Communication is the key. Two-way communication
between clinicians and radiologists is encouraged for a
better patient care.
– Having radiologists in the emergency department will make
a difference.
• There is a different nature of ‘emergency radiology’ from other
radiology 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.
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33. Rule #4
• Prepare the patients
– Plain film radiography and CT
• All sexually-active women must be checked for potential
pregnancy.
• 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.
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34. Rule #4
• Prepare the patients
– Ultrasound
• Depending on the type of exams: fasting, full bladder may be
needed.
• 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.
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35. What to Expect
• Increased volume of patients through the emergency
department.
• Increased volume of radiologic procedures in the
emergency department.
• Increased use of advanced imaging technique for
noninvasive diagnosis and treatment.
• Modern ED incorporates emergency radiology
(plain film radiography, ultrasound and CT) as a
subsection. The ultra-modern ED will have MRI.
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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 multiple
organ injuries ranging from brain, chest,
abdomen/pelvis, spine from cervical down to
thoracolumbar region.
• Stroke protocol: optimized protocol for rapid stroke
diagnosis, diagnosis of ‘salvageable’ brain for
potential anticoagulation treatment or interventions.
• Cervical spine CT for trauma: More accurate and
faster than plain film radiography.
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37. Current Trends in ED Radiology
• Chest CT to rule out PE: Historically difficult
diagnosis becomes easier in seconds of MDCT
scanning.
• Stone protocol abdomen CT: More accurate than
plain film radiograph, faster than IVP and most
importantly, MDCT detects alternative diagnosis such
as appendicitis, gynecologic conditions, etc.
• Bone CT with 3D reformation for complex
fractures: Help in orthopedic treatment planning
such as fractures of the acetabulum, tibial plateau.
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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
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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.
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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
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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.
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