Imaging of the Head and Neck Quiz

See Plain Radiograph. Option B is correct. A plain radiograph is made by sending a beam of X-rays through the body onto a detector plate. Tissues absorb (stop) X-rays to different degrees. Dense tissue such as bone absorbs most of the beam, so very few X-rays get through to the detector, and the part of the image behind bone stays white. Less dense tissue such as muscle and fat absorbs less, so more X-rays reach the plate and the image is darker, and air, which absorbs almost none, looks black. It is the X-rays that reach the detector that darken the image, so more X-rays arriving means a darker picture, which can feel back to front. Because the pattern of absorption is a map of tissue density, plain films are good for bone and joint problems, such as fractures, and give little information about soft tissue. They are cheap, quick and widely available, and carry a much smaller dose of radiation than CT, although it is not zero.

• Absorption: dense bone absorbs most of the X-ray beam.
• Detector: few X-rays get through, so the part of the image behind bone stays white.
• Contrast: less dense tissue lets more through and looks darker, and air looks black.