emergency radiology

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Emergency Radiology: The Basics

Rathachai Kaewlai, MD

www.RadiologyInThai.com

Created: November 2006

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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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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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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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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 back to front of the patients and hit the film in the front of the patients.

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Chest x-ray (PA)

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Chest x-rays of the same patient performed in the same day, in two different projections (above; PA, below; AP).

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’.


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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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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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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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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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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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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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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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 it with your own practice.

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Right Left


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.

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


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.

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

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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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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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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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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Basics: MRI

Various body tissues emit characteristic MR signals, which determine whether they will appear white, gray or black on the images.

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.

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T1-WI

T2-WI

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 and abdomen).

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T1-WI

T1-WI + IV contrast

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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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 examined.

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Normal Doppler US of the lower extremity veins

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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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.

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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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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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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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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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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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. 32

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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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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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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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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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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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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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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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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The information provided in this presentation… 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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