You've probably seen an X-ray or chest x-ray, or you may even have taken one. Ever wondered how to read this exam? When looking at an X-ray, remember that it is a two-dimensional representation of a three-dimensional object: height and width are maintained, but depth is lost. The left side of the image represents the right side of the person and vice versa. Air appears in black, fat in grey, soft tissue and water in lighter gray, and bone and metal in white. The denser the tissue, the whiter it will appear on the X-ray. The denser tissue appears radiopaque and lighter in the image; the less dense, radiolucent or dark.
Part 1 of 4: Making the Initial Checks
Step 1. Check the patient's name
Above all, make sure you're looking at the right X-ray. It sounds obvious, but when you're stressed and under pressure, you can end up skipping some basic stuff. If you got the wrong X-ray, you'll waste time instead of saving.
Step 2. Check patient history
When you're getting ready to read an X-ray, make sure you have all the information about the patient, including their age, gender, and medical history. Remember to compare old X-rays with this one, if there are any others.
Step 3. Read the date of the x-ray
Especially take note of the date when comparing older radiographs. Always check for older exams, if available. The date of the radiograph provides an important context for interpreting findings.
Part 2 of 4: Assessing Image Quality
Step 1. See if the image was taken at full inspiration
Chest X-rays are usually taken when the patient is in the inspiratory phase of the breathing cycle, that is, when the person draws in air. When X-rays pass through the back of the chest into the image, it is the ribs closest to the film, the posterior ones, that are most apparent. You should be able to see 10 posterior ribs if the image is taken at full inspiration.
If you can see 6 anterior ribs, the film is of a very high standard
Step 2. Check the exposure
Overexposed films are darker than usual, and details are harder to see. Poorly exposed films are lighter than they should be and cause areas of opacification to appear. Look for intervertebral bodies on an X-ray of adequate penetration.
- An inferior penetrating X-ray cannot differentiate the vertebral bodies from the intervertebral spaces.
- It will have less penetration if you cannot see the thoracic vertebrae.
- An image with excessive penetration shows the intervertebral spaces very distinctly.
Step 3. Look for rotation
If the patient has not been completely straight against the chassis, there may be rotation evident on the X-ray; in that case, the mediastinum will look very different from normal. You can tell if there is rotation by looking at the clavicular heads and thoracic vertebral bodies.
- See if the thoracic spine lines up at the center of the sternum and between the collarbones.
- Make sure your collarbones are aligned.
Part 3 of 4: Identifying and Aligning the X-Ray
Step 1. Look for bookmarks
The next thing to do is identify the position of the X-ray and align it correctly. Look for relevant markers printed on the radiograph. "L" or "E" represent left. "R" or "D", right. "PA" is posteroanterior; the "AP", anteroposterior, etc. Observe the patient's position: supine (lying), standing, lateral, decubitus.
Step 2. Position the posteroanterior and lateral X-rays
A normal X-ray will consist of a posteroanterior (PA) and a lateral image that are read together. Align them so that they are seen as if the patient were standing in front of you, so that their right side is facing your left side.
- If the images are old, hang them side by side.
- The term posteroanterior (PA) refers to the direction of the X-ray, traversing the patient from the back to the front.
- The term anteroposterior (AP) refers to the direction of the X-ray, traversing the patient from the front to the back.
- The lateral chest radiograph is taken with the left side of the patient's chest against the X-ray chassis.
- Oblique view is rotated between standard front view and side view. It is useful for locating lesions and eliminating superimposed structures.
Step 3. Recognize an anteroposterior X-ray
AP X-rays are sometimes taken, usually just for patients too sick to stand up for a PA X-ray. AP radiographs are usually taken at a shorter distance from the film compared to PA radiographs. Distance lessens the effect of ray divergence and magnification of structures closest to the X-ray tube, such as the heart.
- As AP radiographs are taken from shorter distances, they appear more magnified and less sharp compared to standard APs.
- An AP image may show enlargement of the heart and widening of the mediastinum.
Step 4. Determine if the position is lateral decubitus
An X-ray of this view is taken with the patient lying on their side. It helps to assess suspect fluids (pleural effusion) and whether the effusion is in small cavities or is mobile. You can look at the non-dependent hemithorax to confirm a pneumothorax.
- The dependent lung is likely to increase in density because of atelectasis, caused by the weight of the mediastinum that puts pressure on it.
- If not, the X-ray indicates trapped air.
Step 5. Align left and right
You need to make sure you're looking at the X-ray correctly, and you can do it quickly and easily by looking for the gastric bubble, which should be on the left.
- Assess the amount of gas and the location of the gastric bubble.
- Normal gastric bullae can also be seen in the splenic and hepatic flexures of the colon.
Part 4 of 4: Analyzing the Image
Step 1. Start with an overview
Before focusing on specific details, it's good to look at the image as a whole. The main points you may have skipped may change what you take as reference points. Starting with this overview can also make you aware of looking at things in particular.
Step 2. Check for instruments such as tubes, IV lines, EKG guides, pacemakers, surgical clips, or drains
Step 3. Check the airway
See if the airway is patent and median. For example, in a hypertensive pneumothorax, the airway is deviated from the affected side. Look for the carina, where the trachea bifurcates (divides) into the right and left bronchi of the main trunk.
Step 4. Bones:
check bones for fractures, injuries or defects. Note the overall size, shape and contour of each bone, density or mineralization (osteopenic bones appear thin and less opaque), cortical thickness compared to medullary cavity, trabecular pattern and the presence of erosions, fractures, lytic or blastic areas. Also look for lucent and sclerotic lesions.
- A lucent lesion is an area with decreased density (looking darker); it may look perforated in relation to the surrounding bone.
- A sclerotic lesion is an area of bone with increased density (looking lighter).
- At the joints, look for narrowing or widening spaces, calcification of cartilage, air in the joint space, and abnormal lumps of fat.
Step 5. Look for the silhouette sign
It is basically the elimination of the silhouette or loss of the interface between lung and soft tissue that occurs after a mass or overflow in the lung. Note the size of the cardiac silhouette, the white space that represents the heart between the lungs. When normal, it occupies less than half the width of the chest.
The plastic bottle-shaped heart on the PA film suggests pericardial effusion. Get an ultrasound or a chest CT scan to confirm
Step 6. Check the diaphragm
Look for a straight or raised diaphragm; the former may indicate emphysema. The second may be a sign of an area of consolidation, as in pneumonia, making the lower lung field impossible to distinguish in tissue density when compared to the abdomen.
- The right diaphragm is usually taller than the left because of the presence of the liver below it.
- Also look at the costophrenic angle (which should be acute) to see if there is any rounding, which may indicate effusion (as the fluid settles).
Step 7. Check the heart
Examine the edges of the organ; the edges of the silhouette must be sharp. Note whether radiopacity is obscuring the edge of the heart in the right middle lobe and left lingual, a sign of pneumonia, for example. Also look for abnormalities in the external soft tissue.
- A heart with a diameter greater than half the thoracic diameter is enlarged.
- Look at the lymph nodes and look for subcutaneous emphysema (density of air below the skin) and other lesions.
Step 8. View the lung fields
Start by looking at symmetry and looking for key areas of abnormal lucency or density. Try to train your eyes to go through the heart and upper abdomen to the posterior lung. You should also examine vascularity and the presence of masses or nodules.
- Examine the lung fields for infiltration, fluid, or air bronchograms.
- If fluids, mucus or tumors and the like fill the air sacs, the lungs will appear radiodense (shiny), with less visible interstitial marks.
Step 9. Look at the hilos
Look for lumps and masses in the hila of both lungs. In the front view, most of the hila shadows represent the right and left pulmonary arteries. The last one is always higher up, raising the left hilum.
Look for calcified lymph nodes in the hila, which could be caused by an old TB infection
- Practice leads to perfection. Study and read several chest X-rays to become proficient.
- A good tip for reading chest X-rays is to go from general observations to specific details.
- Always compare old X-rays when they are available. They will help detect new diseases and assess changes.
- Rotation: Observe the clavicle heads in relation to the spinous processes; they should be equidistant.
- Cardiac size should be less than 50% of the chest diameter on PA images.
- Take a systematic approach to reading an X-ray so you don't miss anything.