You've probably seen a chest x-ray or had to do one. Have you ever wondered how to read it? When looking at a plate, remember that it is a two-dimensional image of a three-dimensional structure. The height and width are respected, but the depth is lost. The left side of the image represents the right side of the person, and vice versa. The air appears black, the fat is gray, the soft tissues are indicated with various shades of gray, the bones and metal prostheses appear white. The higher the density of a fabric, the lighter its image on the plate. The denser tissues are radiopaque, while the less dense ones are radiolucent or black on the plate.
Steps
Part 1 of 4: Initial Checks
Step 1. Check the patient's name
First of all, you need to make sure you are looking at the correct x-ray. It may seem like an obvious detail, but when you are stressed and under pressure you can forget even the trivia. If you're looking at the wrong person's x-ray, you're just wasting time instead of saving it.
Step 2. Check the patient's medical history
When you are preparing to analyze the x-ray, make sure you have all the information regarding the patient, including age, sex and medical history. Also remember to compare new x-rays to previous ones if you have them available.
Step 3. Read the date the image was "taken"
Pay particular attention to this, especially when comparing previous x-rays (always look at old x-rays if you can). The date provides valuable information to contextualise and interpret the results.
Part 2 of 4: Judging Image Quality
Step 1. Check that the x-ray was taken during full inspiration
Chest x-rays, generally, must be taken during the inspiratory phase of breathing, that is, when air is brought into the lungs. When the flow of X-rays crosses the front of the chest to the film, the ribs closest to the latter are the posterior ones and also the most evident. You should be able to see ten posterior ribs if the image was detected during full inspiration.
If you can see six front ribs, then the image meets very high standards
Step 2. Check the exposure
Overexposed images are darker than normal and very fine details are difficult to see. On the other hand, underexposed radiographs are whiter than normal and show areas of opacification. Look for intervertebral structures to make sure that the x-ray stream has penetrated the body correctly.
- When the flow has not penetrated sufficiently into the body, you are unable to distinguish the structures from the vertebral spaces.
- If the image is underexposed, you cannot see the thoracic vertebrae.
- Overexposed radiographs show the intervertebral spaces distinctly.
Step 3. Make sure the chest is not rotated
If the patient is not perfectly supported on the X-ray cassette, then you will notice a clear rotation in the image. If this happens, the mediastinum will look abnormal. You can check the rotation by looking at the acromial ends of the collarbones and the structures of the thoracic vertebrae.
- Check that the thoracic portion of the spine is aligned with the center of the breastbone and between the collarbones.
- Make sure your collarbones are aligned.
Part 3 of 4: Identify and Align the X-ray
Step 1. Look for indicators
The next step is to identify the position of the image and align it correctly. Look for the relevant indicators that are printed on the plate. "D" for right, "S" for left, "PA" for postero-anterior and "AP" for anterior-posterior and so on. Also take note of the patient's position: supine (on the back), upright, lateral, decubitus, and so on.
Step 2. Place radiographs in postero-anterior and lateral projection
A normal chest radiograph includes both postero-anterior and lateral projections, and both must be analyzed simultaneously. Line them up as if you are looking at the patient in front of you, so that their right side is to your left.
- If you are also examining old x-rays, you should hang them adjacent to the new ones.
- The term postero-anterior (PA) indicates the direction in which the X-ray beam has crossed the person's body, that is, from the back to the front (from back to front).
- The term anteroposterior (AP) refers to the fact that the beam of rays passed through the patient's body from front to back (front to back).
- Lateral views are obtained by placing the patient so that the left side of his chest rests against the x-ray cassette.
- An oblique projection is obtained with a rotated and intermediate position between the standard front and side ones. It can be useful when it is necessary to locate lesions and eliminate the image of overlapping structures.
Step 3. Recognize an anterior-posterior (AP) x-ray
Sometimes this type of image is chosen, but only for patients who are too sick and weak who are unable to maintain a vertical posture for the posteroanterior projection. The AP radiographs, when compared to the PA radiographs, are taken with a shorter distance from the film. This decreases the divergence effect of the X-ray beam and the enlargement of the structures closest to the tube that emits the beam, such as the heart.
- Since an AP x-ray is taken at shorter distances, then the image is larger and less sharp than those in PA.
- An AP x-ray shows an enlarged heart and an enlarged mediastinum.
Step 4. Determine if it is a lateral decubitus image
In this case, the patient is lying on his side. This projection allows to determine the suspected presence of fluid (pleural effusion) and to demonstrate whether this effusion is localized or mobile. You can observe the upper thorax to confirm a pneumothorax.
- The lung positioned towards the support table should have a higher density. This effect is due to atelectasis caused by the pressure exerted by the weight of the mediastinum.
- If this does not happen, it means that there is trapped air.
Step 5. Align the left and right sides
You need to be sure you are looking at the x-ray correctly. You can do this easily and quickly by looking at the bottom of the stomach which should be on the left.
- Determine the amount of gas present in the bottom of the stomach.
- You may also notice normal gas bubbles in the splenic and hepatic flexure of the colon.
Part 4 of 4: Analyzing the Image
Step 1. Start with a general observation
Before focusing on specific details, it is always worth looking at the chest as a whole. The main things that you may have ignored could change the standards on which to base the rest of the observation, standards that must be adopted as reference points. Furthermore, a general look allows you to be even more careful in observing anomalous details.
Step 2. Check if you see the image of some instruments such as tubes, intravenous catheters, ECG electrodes, pacemakers, surgical clips or drainage catheters
Step 3. Check your airways
Be sure to see the patient's airways and midline. For example, in the presence of a tension pneumothorax, the airways are diverted away from the affected area. Observe the tracheal keel, which is the point where this tubular structure forks (divides) into the two main bronchi, right and left.
Step 4. Bones:
check the bones for any type of fracture, injury or defect. Observe its general size, shape and profile, evaluate its density or mineralization (bones suffering from osteopenia are less opaque and thinner). Take note of the cortical thickness in relation to the medullary cavity, the trabecular structure, the presence or absence of erosions, fractures, lytic or blastic lesions. Also look for sclerotic or translucent lesions.
- A shiny bone lesion is a not very dense area (which appears darker); it may have a pitted appearance compared to adjacent bony areas.
- A sclerotic lesion is an area of the bone with greater density (which appears whiter).
- At the level of the joints, check for narrow, enlarged spaces, signs of cartilage calcification or abnormal accumulations of fat.
Step 5. Check for loss of mediastinal lines
If you cannot detect these reference lines from the image, it means that the soft tissue between the lungs is not visible, which happens when there is a mass in the lungs or after an effusion. Also observe the dimensions of the heart space: it should occupy less than the width of half the chest.
Be careful if you notice a heart shaped like a water bottle in a PA projection, as this anomaly suggests a pericardial effusion. In this case it is good to request an ultrasound or a chest computed tomography to have confirmation
Step 6. Look at the diaphragm
Check if it's raised or flat. A flattened diaphragm is a sign of emphysema. A raised diaphragm indicates an area of consolidation of the lung space (as in pneumonia), which, from a tissue density point of view, makes the lower lobe of the lung indistinguishable from the abdomen.
- The right area of the diaphragm is usually higher than the left one, due to the presence of the liver just below it.
- Also observe the costophrenic angle (which should be acute) in search of any anomaly or dilation that could indicate an effusion (fluids that are deposited).
Step 7. Check the heart
Examine the edges - the edges of this muscle should be well defined. Check for radiopacity that prevents good observation of the heart contour, as occurs, for example, in pneumonia affecting the right median lung lobe and left lingula. Also, take note of any external soft tissue abnormalities.
- A heart with a diameter larger than that of the hemithorax indicates cardiomegaly.
- Also look at the lymph nodes, look for subcutaneous emphysema (a density that indicates air under the skin) or other lesions.
Step 8. Also check the lung lobes
Start by looking at their symmetry and looking for large abnormal areas of poor radiopacity or density. Try exercising your eyes to peer through the heart and upper abdominal to look at the back of the lungs. You should also check the vascularity, the possible presence of masses or nodules.
- Examine the lung lobes for leaks, fluid, or air bronchogram.
- If liquid, blood, mucus or a tumor fills the air sacs, the lungs appear radiodense (luminous) with less visible interstitial signs.
Step 9. Look at the pulmonary ili
Check for lumps or masses in the ili of both lungs. In a frontal projection, most of the shadows you notice on the hilum are due to the left and right pulmonary arteries. The left pulmonary artery is always higher than the right, thus making the left hilum itself higher.
Check for calcified lymph nodes in the hilar area, which could be caused by an old tuberculosis infection
Advice
- Practice makes perfect. Studying and reading many chest x-rays will make you very proficient in this field.
- Always compare the images you have with previous ones if you can. This way you can identify new diseases and evaluate changes.
- As a general rule, when observing a chest X-ray, we start from a general reading to an increasingly detailed one.
- Rotation: observe the acromial ends of the clavicles in relation to the spinous process, they should be equidistant.
- The size of the heart, in the X-ray image, should be less than half the thoracic diameter.
- Follow a systematic method when reading a chest x-ray to make sure you don't overlook any details.
