Chest X-Ray Interpretation Basics

A chest radiograph is a projection, not a direct photograph of the lungs. Structures are superimposed, and the projection can create apparent enlargement or opacity. Before interpreting disease, establish what the image can reliably show. Confirm the patient, date, side marker, projection, position, and comparison studies. A standard erect PA film places the heart closer to the detector and reduces magnification. A portable AP film is often obtained in the emergency department or intensive care unit, but the x-ray beam travels from front to back while the heart is farther from the detector. The heart and mediastinum therefore appear larger. An AP film is useful for acute change and device position, but it cannot reliably establish cardiomegaly. Assess rotation by comparing the medial ends of the clavicles with the spinous processes. Rotation can make one hemithorax appear more opaque and can distort the mediastinum. Assess inspiration as well; low lung volume crowds the vascular markings and may mimic basal opacity or exaggerate heart size. Exposure matters: an underpenetrated film can make the lungs look diffusely white, while an overpenetrated film...