Planar radiography was the earliest clinical application of x-ray imaging and is still the most widely used imaging tool. In a planar radiograph, x-rays travel through the patient’s body, where they are partially absorbed by anatomic tissues, and the transmitted x-rays are detected by lm or by a digital detector to form the image. In this image, the complex 3D anatomy is projected onto the 2D plane of the x-ray detector. As a result, normal anatomy can hide anomalies, or summation of structures can mimic an abnormality. Both situations can potentially result in a misdiagnosis. is limitation is addressed by tomosynthesis, which adds some (but not complete) depth resolution to the planar radiograph.