RADIOLOGY & MEDICAL IMAGING IN Contrast enhanced radiographs: A substance is injected into the
REHABILITATION body to increase the contrast of the image of the desired structure.
Contrast media can be radiopaque (positive contrast), radiolucent
(negative contrast) or a combination of the two (dual contrast).
Arthrography: A contrast agent is injected into the joint space.
Overview of radiology and medical imaging as related to the practice The agent can be positive (for ex. iodide solution) or negative
of physical therapy, as well as basic methods of identifying and (air) or a combination of the two. The contrast material outlines
interpreting various images. Emphasis will be placed on recognizing internal structures and is often used to demonstrate capsular tears
the type of image being viewed, tissues displayed, indications and or cartilaginous abnormalities.
limitations for various imaging techniques. You will learn orientation Myelography: Contrast is injected into the subarachnoid space
of the images, key landmarks, and methods of briefly assessing films of the spinal cord to evaluate the spinal cord, nerve roots, dura
and images, plus practical hints to quickly differentiate MRI from CT and surrounding structures.
images. Emphasis will be placed on enhancing the therapist’s ability
Angiography: Contrast material is injected directly into the
to gather fundamental information and to knowledgeably
arterial or venous systems to evaluate the circulatory system.
communicate with referring physicians regarding radiological/nuclear
Very useful in the evaluation of trauma, to map out bone lesions,
imaging findings and effectively recommending therapies.
to demonstrate the vascular supply of a tumor and for planning
Objectives: Diskography: Injection of contrast material into the nucleus
pulposus. Normally combined with CT to evaluate low back
You will be able to: pain. Normally performed after conservative treatment has
1) Develop fundamental understanding of the interpretation and failed and when other imaging modalities (MRI, CT and
language of commonly used imaging techniques. myelography) have proven equivocal with respect to the design
2) Identify the indications, limitations, and strengths of various of the appropriate surgical intervention.
imaging techniques utilized in diagnosis and patient rehabilitation.
Radiology: Traditionally the branch of medicine that deals with
radioactive substances including x-rays, radioactive isotopes and
CT is a technology that uses x-rays to create cross-sectional (axial,
ionizing radiation. Recently there has been significant advancement in
sagittal, or coronal) images on a polyvinyl film sheet. CT is the same
imaging technology to include imaging methods that don’t involve
thing as a CAT scan. The x-ray beam is moved around the patient, the
ionizing radiation such as ultrasound and magnetic resonance imaging
radiation strikes detectors that are either stationary or move in
(MRI). These advancements have generated new designations of the
coordination with the x-ray tube. A computer then creates a 2
field such as medical imaging and diagnostic imaging.
dimensional image of the area scanned.
Orthopedic radiology: Radiological diagnostic evaluation of the
CT is imaged cross-sectionally, like a loaf of bread, with the slice
musculoskeletal system. The primary tool is plain film radiology
thickness ranging from 7-10mm. The CT advantage over plain film
although other techniques such as MRI are common.
radiographs is reduction of tissue overlap and increased sensitivity to
density. There is less difficulty sorting out superimposed or
Radiograph: An x-ray film with an image of an anatomical part.
overlapping structures than with x-ray technique and greater ability to
Radiographs are formed when x-rays emanating from a localized
reveal subtle differences in tissue density. You can see more with less
source pass through a portion of the body and onto a detector (film
confusion on CT.
plate) that records the density of x-rays as an image.
Because it is an x-ray modality, CT uses the same basic principles of
Plain film/conventional radiograph: A radiograph made without
exposure and contrast as plane film radiology and the images created
contrast enhancement or other modifications. Plain radiographs
have the same tissue density to gray scale relationships. This is an
account for approximately 80% of imaging examinations.
important concept to remember because much of what you know
about x-ray technology and interpretation is the SAME for CT scans.
Review the chart below indicating tissue density and gray scale
Specific anatomic areas of interest on a CT study are referred to as 6. Read CT’s images in rows as you would a page of print, left to
“windows”. The human eye can detect a limited number of shades of right, top to bottom. The images typically move sequentially from
gray, whereas a computer can detect thousands of shades. By superior to inferior. . Again, note the “scout” exposure to orient
enhancing the gray contrast in desired regions of a CT scan, soft yourself.
tissue details can be made more appreciable to the eye. By setting a
“narrow” window, grays are displayed only for a limited range of Magnetic Resonance Imaging
densities, a “wide” window spreads the gray scale across more tissue
densities. Anything denser than the window setting-in HU units- will MRI is more expensive and more complicated than CT to produce but
appear white and structures less dense than the window setting appear generates a somewhat similar image. In fact, without some practice,
black. Again, the goal is to create an appreciable range of grays the two are difficult to tell apart at times. MRI is the same as nuclear
within the tissue or region of interest to aid visual differentiation of magnetic resonance that you may remember from the old days in
similar density tissues. organic chemistry. MRI is essentially the imaging of protons. To
produce an MRI image the patient or body part is placed in a
Other Types of CT superconducting magnet. A strong magnetic field is generated by a
current moving through a series of helical coils. Protons have a
Helical tomography uses a high speed gantry or mobile x-ray head, natural spin frequency and resultant magnetic field. As the external
which moves about the patient in a spiral fashion. The entire body can magnetic field is created around them, protons behave like pieces of
be imaged in about 90 seconds. This method also excels at metal near a magnet: hydrogen atoms move to one of two poles.
demonstrating vascular structures and is called CT angiography. A
contrast medium is injected into the veins and a rapid image made. A radio-frequency signal is then pulsed through the atoms . The radio-
frequency used is the same as the natural pulse frequency of the
Other forms of CT are “ultrafast” requiring just a few seconds for spinning proton causing it to absorb the radiowave energy and
exposure of large body segments and 3D-CT which produces stunning resonate. Once the MRI machine’s radio wave is shut off the protons
three-dimensional detail. revert back or decay to their old natural steady state. In doing so they
give off a radiosignal that can be detected by a radiowave receiver
and converted, via computer, to an image. So, the more hydrogen a
What is CT good for? tissue contains the more intense the signal produced, and the brighter
or whiter the image.
Fracture detection and evaluation This makes the image a bit different than CT because MRI is NOT an
Spine alignment x-ray. The image intensity corresponds to the amount of hydrogen in
Intracranial hemorrhage the tissue not the molecular density of tissue. Bone, for example, is
Abdominal injury very dense to an x-ray beam but contains little hydrogen (water) and
Detection of foreign bodies (especially in joints) so yields a weak, dark, MRI signal and resultant image.
Diagnosis of neoplasms of liver, lung, kidney, & bone
Tumor staging To add to the confusion you will see on MRI films and radiology
reports the terms “T1” and “T2”. The terms describe two different
Reading a CT times at which a signal is recorded and the two techniques yield
different gray tones for tissues. T1 decay is the early part of the decay
1. Identify the “scout” image. The scout image is digital x-ray of the signal, just after the MRI machine shuts off its radio-frequency pulse.
subject area appearing in a corner of the first film sheet. The scout If the radio receiver listens late in the decay period it hears the T2
image will give you information on what levels and where the image signal. Again, the images look different. In T1 images fat is bright
was gathered. white and water is gray; in T2 images fat is gray and water is
white. One memory help is World War II (water is white on T2).
2. Lines will be drawn through the image on the scout film showing
where the essential images were taken. All other images on the film To distinguish a CT from an MRI look at the fat: fat is bright white on
sheet are slices located between these lines. Think of the essential a T1 image and gray to black on a CT. Then look at bone. Bone is
images as landmarks with subsequent images moving, from superior white on CT and gray (medullary) or black (cortical) on MRI. Also
to inferior, toward the next essential image. CT scans will display kVp and mA exposure settings alerting you to
the X-ray nature of the image.
3. There may be several (1-10) sheets of images for one examination.
Radiologists will often number them with a marker. Also on the left T1 bright tissues:
top of each image will be several lines of exposure information Fat
including the exposure number. These numbers begin at one on the Blood
first page and continue through the last film. There may be may many
dozens of images on multiple plastic sheets for a single study. T2 bright tissues
4. The top, bottom, and sides of each image will be labeled A- Inflammatory masses
anterior, P-posterior etc. So, in a brain image the top may read AS for Joint fluid
anterior superior (oblique angle) and the L and R will be noted.
5. Note that CT images are backward, the patients right is on your
left. You may feel as though you are looking up and through the
patient from foot to head. Normally each image will display a small L
and R for orientation.
Advantages of MRI over CT RADIOLOGY FOR THE PHYSICAL THERAPIST
Focus: Plain / Conventional Radiographs
No ionizing radiation
Multi-plane imaging capability: axial, coronal, sagittal, oblique.
Better anatomic detail: but changing fast as CT advances The essential language and skills of orthopedic plain radiograph
More sensitive to subtle tissue alterations in bone marrow interpretation and a practical method of analysis of normal and
Often better tissue contrast than with CT abnormal anatomy will be discussed.
But…it is more expensive.
Reading an MRI You will be able to:
1) Develop a fundamental understanding of the interpretation and
1. Locate the “scout” image. It will be taken at 90 degrees to the language of plain-film radiology.
subsequent views so that you can see where the “slices” are made for 2) Analyze the radiographic appearance of normal bone and soft
each view. That is: a scout film shot in the sagittal plane will tissue.
demonstrate transverse lines from proximal to distal. The images that
follow are transverse plane images. What is X irradiation, how is it produced in an X-ray
machine, & how is it used to make a radiograph?
2. Look at the top, bottom, and sides of the images on the film sheet.
A letter and number are present. The letter will be A for anterior, P
for posterior and R and L. Or, on a sagittal image R, L, S-superior and X-rays are a short wave high-energy form of Electro-Magnetic
Inferior. Radiation located just below gamma rays on the EMR scale. As with
all EMR, X-rays behave as both a particle and a wave. When an X-ray
3. As with CT, read the sequential images from left to right, top to particle moves through body tissues it may or may not strike atomic
bottom on each film. structures of the body. If it does strike or contact the atomic particles
of the body, the X-ray particle will be either absorbed or deflected.
Nuclear Imaging / Radioisotope Scanning: The more “dense” the tissue, or the higher its average molecular
weight, the more likely an X-ray particle will deflect and not pass
Radio-pharmaceuticals are administered to the patient. The isotopes through the body.
are designed to be concentrated in specific types of tissues, and
therefore, provides functional data. X-ray machines are somewhat like an incandescent light bulb. The
machine focuses a high-energy beam of electrons on a tungsten
In orthopedic and physical therapy practice, the most common type of filament, which releases X-ray radiation in all directions. A focused,
nuclear imaging seen is Technetium bone scanning. Technetium-99m or directionalized, beam is created within the head of the machine and
is a radioactive tracer. It is injected as a few cc’s of liquid into a vein coned to the desired size and shape by a “collimator”. The beam is
of the arm and allowed to circulate for several hours. Technetium- projected on a radiographic plate consisting of a sheet of plastic
99m is absorbed by bone cells in relationship to metabolic activity: covered with a thin silver halide emulsion. X-rays striking the film
the more active the osteocytes the more T99 absorbed. An image of plate cause the silver iodide emulsion to fix or adhere to the film’s
the bone, taken with a gamma camera, shows “hot” spots seen as plastic creating a black area. Where no rays hit the film, no emulsion
black spots on areas of bone which are most active. The images may sticks and the area will become clear, seen as white. Regions of
be of the entire body or just a particular region, and are not well intermediate exposure produce a gray scale.
focused or resolved. You are looking at both a black and white image;
either the area is hot or it is not. A “hot” area gives you a generic Cassettes are lightproof metal cases for the x-ray film. Cassettes
diagnosis: inflammation, fracture, postoperative bone healing, contain “intensification screens” which increase the image saturation
infection, metabolic disease etc. All you know is that spots of bone on the film.
are metabolically active: you do not know why, other than possibly by
history. The benefit of scanning is very early detection. In post- TIDBIT :-) To demonstrate you are “in the know” always refer to
operative cases where bone infection is suspected, a technetium scan an x-ray film as a “film”, “image”, or “radiograph” but never call it an
can detect a problem days before either CT or plane film x-rays would “X-ray”.
Tissue Density and the Gray Scale
Early detection of possible stress fractures 1. Radiographs produce an image in a bright white to dark black color
Early detection of osteomyelitis gradient resulting from the density of the material being X-rayed.
Knowing which tissues correlate to which color density is the key to
interpreting X-ray images.
Location of bone metastases from known or suspected cancer
2. Images can also be under or overexposed. An underexposed film Hint: If structures appear odd or distorted on a film, check to see if
results from inadequate x-ray particle penetration and appears overly the patient was injured, in pain, ill, or otherwise unable to be
white. Excessive particle penetration produces an overexposed film positioned correctly before assuming pathology.
that appears blackish. There are two ways, in the exposure setting of
the machine, to produce this error. Radiographic Views
Nomenclature of Density: View names typically describe the beam entry and exit. An anterior-
posterior view implies the beam entered the patient anteriorly and
1. Opaque: white or relatively whiter areas on the film such as bone, exited posteriorly. A lateral view enters and exits from the sides and
or, normally black areas which appear whiter than normal are an oblique views from an angle. A marker will be located on the film
referred to as “areas of density”, being “dense”, “areas of increased indicating R or L.
opacity” or an “opaque area”
AP: common view of extremities, spine, head, hands and feet.
2. Density: same as opacity, e.g. areas of “increased density” or An AP of the chest suggests a sick or bedridden patient because
“showing increased density”. a PA is preferred. Keep in mind amplification and elongation.
The heart will appear enlarged in an AP view of the chest. AP
3. Sclerosis: an increase in density in bone. Associated with and PA chest views are usually labeled as such.
degenerative arthritis in subchondral bone. Associated with avascular PA: most common chest view; also common at the wrist/hand.
necrosis post fracture. “Sclerosis is noted at the scaphoid bone” or Lat: lateral view, head, chest, extremities, spine
“there is bony sclerosis of the proximal phalangeal periarticular Oblique Views: may be labeled right or left oblique, medial-
bone”. lateral oblique etc to indicate orientation. Common in
extremities, spinal films, mammography
4. Radiolucency: low density tissues which appear more gray or Dorsal plantar: an AP view of the foot
black. The lungs are more radiolucent, or “lucent” than the heart. Special views: there are many body regions best visualize with
particular “special views” such as the “odontoid”, “swimmers”, or
5. Lucency or Lucent: same as radiolucency- the lungs are “clear “sunrise” views you may see or read about in reports.
and lucent”. “The midshaft of the femur demonstrates an area/region
of lucency”. “One view is NO view”. X-ray studies are always multiple views. A
single view or angle of anything is considered inadequate for
Remember you are viewing a two dimensional representation of a conclusive comment. It is quite common to see pathology on one
three dimensional object. Density can be produced in several ways. view only to discover that it does not exist on other views. This gets
true density of the material being X-rayed us all in trouble now and then. One view may reveal “possible”
superimposition of several low density structures findings but it is not conclusive. Don’t forget the comparison views
superimposition of medium density structures of any extremity film. Look at the contralateral side to determine what
Be careful here: overlap or superimposition of two or three normal
structures will create odd appearing lines, regions, and shadows of
variable density giving the appearance of a structural abnormality. A Scheme for Reading Radiographs
Check surrounding anatomy before you declare an abnormality.
To avoid “locking in” on the obvious and missing the subtleties, you
Radiographic Distortion will want to develop an ordered method of reading films. Learn to
look at the whole film, systematically, step-by-step, before making
Like a flashlight beam, x-rays leaving the collimator are expanding in comment. Here is one system for you to try:
a conical pattern. This creates several sources of distortion that may
First - Orient Yourself
1. Magnification: body parts closest to the beam source are enlarged
and show less resolution or image sharpness on the film and body 1. Read the labels: check the patient’s name, date of film, and view
regions farthest from the beam source show less enlargement and markers for information.
greater image resolution. Stated backwards: structures lying closest to
the film plate demonstrate the best resolution and least enlargement. 2. Place the film in the view box: orient a chest PA or AP, head,
abdominal, and extremity film in the viewing box with the patient
For example: important chest structures, the heart and lungs, are facing you. The patient’s Right is on your Left. Double check to avoid
located somewhat anteriorly within the thoracic cavity. To minimize embarrassment. Fingers and toes point up, hands and feet oriented
amplification and maximize image sharpness you would place the right on right and left on left. Lateral views typically face to your left.
patient with the anterior chest nearest the film cassette. This is a PA
view of the chest and is most common. 3. Orient yourself: Where are you? What are you looking at; what
anatomy can you identify; which vertebrae are you looking at?
2. Foreshortening and Elongation: when an image is made with the Develop some points of orientation such as C7, T12, or the SI joint
x-ray beam approaching the subject from an angle the object will that you can use each time.
appear shorter in length on the film. If the structure being filmed is
not lying flat on the x-ray table/film cassette the end of a bone for TIDBIT :-) To be really impressive SNAP the film firmly and
example, closest to the beam source will appear larger/longer than the authoritatively into the view box. This is important body language.
portion of the bone furthest from the beam source.
Second - The ABC’S of Reading a Film
Architecture: size, shape, extra or missing bones
Contours: trace cortical and medullary outlines of each bone-
follow any possible “fractures” from start to finish. Often they
are lines of tissue superimposition which will continue beyond
the bone and are not fractures.
Note spurs, surgical sites: drill holes, grafts, irregularities in
cortex and periosteum.
Alignment: relationships such as spinal lines, dislocations,
White: sclerosis, tumor encapsulation, avascular necrosis, repair
Gray: post trauma bone resorption, osteopenia
General bone density: Loss of a distinct cortical image and loss of
contrast between bone and soft tissues indicate decreased bone mass.
Local bone density: Areas of increased density (sclerosis) are
normally signs of repair following a stressful stimulus.
Narrow joint spaces: may be DJD
Wide joint spaces: effusion secondary to trauma, arthritis, infection
Subchondral bone: cysts, sclerosis
In osteoarthritis subchondral bone becomes sclerotic whereas there is
no reparative sclerosis in rheumatoid arthritis.
Epiphyseal plates: open, closed, intact, sclerotic, age estimate.
Epiphyseal plates are cartilaginous and are bounded by a smooth
margin with a band of sclerosis indicating increased bone forming
activity. Epiphyseal plates commonly appear “moth eaten” and
irregular. Fractures here may be difficult to assess. Compare with
film of opposite side.
Muscles: Plain films do not show muscle definition well. Gross
hypertrophy, edema, or atrophy can be observed.
Fat Pads and Fat Lines: The displacement of fat pads or fat lines from
their normal position is usually due to edema often secondary to
Joint capsules: Normally difficult to observe but can become visible
when distended by effusion.
Periosteum: Normally difficult to observe but can be seen under such
conditions as fracture healing, following osteomyelitis, and with
malignant bone lesions.
Read the entire film from “A to S”. Beware the charm of
the obvious: it will distract you from the subtle.