Ways of producing images of body organs that record, process and analyse sound waves, radio waves or X-RAYS passing through or generated by the body's tissues. ULTRASOUND scanning using high-frequency, inaudible sound waves directed at the area of the body being studied is the most generally used scanning procedure. Sound waves are reflected more powerfully by some structures than others, and a pattern of those reflections is detected and shown on a screen. Other screening methods include COMPUTED TOMOGRAPHY (CT), magnetic resonance imaging (MRI), positron emission tomography (PET SCANNING) and RADIONUCLIDE scanning, which measures the differential uptake of radioactive materials in the body's tissues.