Reading a chest X-ray

You can think of X-rays as high-energy photos that penetrate the body tissues so that we can see what’s going on inside. Just like visible light, X-rays are less likely to penetrate denser materials. Conventional x-rays that show white bones on a black background are like photographic negatives.

The darkest parts of the film like the lungs are areas where more photons can penetrate the body. In contrast, the sharp, bright white areas are where the dense bone material blocks photons from getting through.

Let’s go through this chest X-ray using an easy-to-remember checklist - associated with the first 7 letters of the alphabet: ABCDEFG.

A stands for Assessment. To avoid errors and wasted time, you should always begin by assessing the patient and exam data. You want to verify the patient’s data with the exam data (medical record number, date of the exam, etc.) to ensure that you are looking at the right study and patient.

You also need to assess image quality, because this will impact the accuracy of the test in detecting pathology. For example, to ensure there isn’t excess rotation of the patient, you should make sure that the medial ends of the spinous processes are equally distant from the border of the vertebral bodies.

Rotation throws off the usual X-ray anatomy and introduces unwanted variation. Next, a good inspiration film should show at least the 10th or 11th posterior ribs.

If the lungs are not fully expanded, we might miss important diseases. Finally, we need to make sure that the exposure isn’t too bright or too dark.

To check for this, you can look for fine markings in the lung fields to make sure they are visible. If the fine lung markings aren’t visible, then the X-ray may fail to detect some diseases.

A also reminds us to make sure there isn’t “Air where it shouldn’t be.” Finding air where it should not be - or more commonly “ruling it out” - remains one of the most important uses of medical X-rays.

Diagnoses like pneumothorax, pneumomediastinum, pneumoperitoneum, and subcutaneous emphysema are all examples of “air where it shouldn’t be.” All of these are surgical emergencies and can be diagnosed by a simple chest X-ray.

Finally, if the major airways like the trachea are bent or deviated, (Another example of air where it shouldn’t be), may signal an underlying mass.