X-ray reading

[abu3li]

You have probably seen a chest x-ray (chest
radiograph), or might even have had one taken.
Have you ever wondered how to read a chest x-
ray? Here is a quick and easy approach by
following these simple steps and using the
mnemonic 'A,B,C,D,E,F,G,H,I'

When looking at a radiograph, remember that it
is a 2-dimensional representation of a 3-
dimensional object. Height and width are
maintained, but depth is lost. The left side of the
film represents the right side of the individual,
and vice versa. Air appears black, fat appears
gray, soft tissues and water appear as lighter
shades of gray, and bone and metal appear
white. The denser the tissue, the whiter it will
appear on x-ray. Denser tissues appear
radiopaque, bright on the film; less dense
tissues appear radiolucent, dark on the film.

Check the patient 's name. Above all
else, make sure you are looking at the
correct chest x-ray first.
Read the date of the chest radiograph.
Make special note of the date when
comparing older radiographs (always look at
older radiographs if available). The date the
radiograph is taken provides important
context for interpreting any findings. For
example, a mass that has become bigger
over 3 months is more significant than one
that has become bigger over 3 years.
Note the type of film (while this article
assumes you are looking at a chest x-
ray, practice noting if it is a plain film, CT,
angiogram, MRI, and so forth).

For chest x-ray, there are several views as follows:

The standard view of the chest is the
posteroanterior radiograph, or "PA
chest." Posteroanterior refers to the
direction of the x-ray traversing the
patient from posterior to anterior. This
film is taken with the patient upright, in
full inspiration (breathed in all the
way), and the x-ray beam radiating
horizontally 6 feet (1.8 m) away from
the film.

The anteroposterior (AP) chest
radiograph is obtained with the x-ray
traversing the patient from anterior to
posterior, usually obtained with a
portable x-ray machine from very sick
patients, those unable to stand, and
infants. Because portable x-ray units
tend to be less powerful than regular
units, AP radiographs are generally
taken at shorter distance from the film
compared to PA radiographs. The
farther away the x-ray source is from
the film, the sharper and less
magnified the image. (You can confirm
this by placing your hand about 3
inches from a desk, shining a lamp
above it from various distances, and
observing the shadow cast. The
shadow will appear sharper and less
magnified if the lamp is farther away.)
Since AP radiographs are taken from
shorter distances, they appear more
magnified and less sharp compared to
standard PA films.

The lateral chest radiograph is taken
with the patient's left side of chest
held against the x-ray cassette (left
instead of right to make the heart
appear sharper and less magnified,
since the heart is closer to the left
side). It is taken with the beam at 6
feet (1.8 m) away, as in the PA view.
An oblique view is a rotated view in
between the standard front view and
the lateral view. It is useful in
localizing lesions and eliminating
superimposed structures.
A lateral decubitus view is one taken
with the patient lying down on the
side. It helps to determine whether
suspected fluid (pleural effusion) will
layer out to the bottom, or suspected
air (pneumothorax) will rise to the top.
For example, if pleural fluid is
suspected in the left lung, check a left
lateral decubitus view (to allow the
fluid to layer to the left side). If air is
suspected in left lung, check a right
lateral decubitus view (to allow the air
to rise to the left side).
Look for markers: 'L' for Left, 'R' for
Right, 'PA' for posteroanterior, 'AP' for
anteroposterior, etc. Note the position of the
patient: supine (lying flat), upright, lateral,
decubitus.

Note the technical quality of film.
Exposure: Overexposed films look
darker than normal, making fine details
harder to see; underexposed films look
whiter than normal, and cause
appearance of areas of opacification.
Look for intervertebral bodies in a
properly penetrated chest x-ray. An
under-penetrated chest x-ray cannot
differentiate the vertebral bodies from
the intervertebral spaces, while an
over-penetrated film shows the
intervertebral spaces very distinctly.
To assess exposure, look at the
vertebral column behind the heart
on the frontal view. If detailed
spine and pulmonary vessels are
seen behind the heart, the
exposure is correct. If only the
spine is visible, but not the
pulmonary vessels, the film is too
dark (overexposed). If the spine
is not visible, the film is too white
(underexposed).

Motion: Motion appears as blurred
areas. It is hard to find a subtle
pneumothorax if there is significant
motion.

Rotation: Rotation means that the
patient was not positioned flat on the
x-ray film, with one plane of the chest
rotated compared to the plane of the
film. It causes distortion because it can
make the lungs look asymmetrical and
the cardiac silhouette disoriented.
Look for the right and left lung fields
having nearly the same diameter, and
the heads of the ribs (end of the
calcified section of each rib) at the
same location to the chest wall, which
indicate absence of significant rotation.
If there is significant rotation, the side
that has been lifted appears narrower
and denser (whiter) and the cardiac
silhouette appears more in the
opposite lung field.

Airway: Check to see if the airway is
patent and midline. For example, in a
tension pneumothorax, the airway is
deviated away from the affected side. Look
for the carina, where the trachea bifurcates
(divides) into the right and left main stem
bronchi.

Bones: Check the bones for any
fractures, lesions, or defects. Note the
overall size, shape, and contour of each
bone, density or mineralization (osteopenic
bones look thin and less opaque), cortical
thickness in comparison to medullary cavity,
trabecular pattern, presence of any erosions,
fractures, lytic or blastic areas. Look for
lucent and sclerotic lesions. A lucent bone
lesion is an area of bone with a decreased
density (appearing darker); it may appear
punched out compared to surrounding
bone. A sclerotic bone lesion is an area of
bone with an increased density (appearing
whiter). At joints, look for joint spaces
narrowing, widening, calcification in the
cartilages, air in the joint space, abnormal
fat pads, etc.

Cardiac silhouette: Look at the size of
the cardiac silhouette (white space
representing the heart, situated between the
lungs). A normal cardiac silhouette occupies
less than half the chest width.
Look for water-bottle-shaped heart on
PA plain film, suggestive of pericardial
effusion. Get an ultrasound or chest
Computed Tomagraphy (CT) to
confirm.

Diaphragms: Look for a flat or raised
diaphragm. A flattened diaphragm may
indicate emphysema. A raised diaphragm
may indicate area of airspace consolidation
(as in pneumonia) making the lower lung
field indistinguishable in tissue density
compared to the abdomen. The right
diaphragm is normally higher than the left,
due to the presence of the liver below the
right diaphragm. Also look at the
costophrenic angle (which should be sharp)
for any blunting, which may indicate
effusion (as fluid settles down). It takes
about 300-500 ml of fluid to blunt the
costophrenic angle.

Edges of heart; External soft
tissues: Check the edges of the
heart for the silhouette sign : a radioopacity
obscuring the heart's border, in right middle
lobe and left lingula pneumonia, for
example. Also, look at the external soft
tissues for any abnormalities. Note the
lymph nodes, look for subcutaneous
emphysema (air density below the skin), and
other lesions.

Fields of the lungs: Look for
symmetry, vascularity, presence of
any mass, nodules, infiltration, fluid,
bronchial cuffing, etc. If fluid, blood,
mucous, or tumor, etc. fills the air sacs, the
lungs will appear radiodense (bright), with
less visible interstitial markings.
Gastric bubble: Look for the
presence of a gastric bubble, just
below the heart; note whether it is obscured
or absent. Assess the amount of gas and
location of the gastric bubble. Normal gas
bubbles may also be seen in the hepatic
and splenic flexures of the colon.

Hila: Look for nodes and masses in
the hila of both lungs. On the frontal
view, most of the hilar shadows represent
the left and right pulmonary arteries. The left
pulmonary artery is always more superior
than the right, making the left hilum higher.
Look for calcified lymph nodes in the hilar,
which may be caused by an old
tuberculosis infection.
Instrumentation: Look for any tubes
(e.g. tracheal nasogastric), IV lines,
EKG leads, pacemaker, surgical clips, drains,
prostheses, etc.

Steps
Practice makes perfect. Study and read
numerous chest x-rays to become proficient
therein.
A good rule of thumb for reading chest x-
rays is to go from general observations to
specific details.

Rotation: look at the clavicles' heads in
relation to the spinous processes - they
should be equidistant.

Always compare with old x-rays whenever
available. They will help you detect new
disease and evaluate for changes.
The cardiac size should be < 50% the
diameter of the chest on PA film.
Follow a systematic approach to read a
chest x-ray to make sure that you do not
miss anything.