Computer-assisted tomography.

A remarkable and fundamentally new radiological technique has recently become available and has been in clinical use in North America since July 1973. In this British invention, the originality of the method lies essentially in the use of a small computer for processing of x-ray photon attenuation data, as measured by sodium iodide crystal detectors. From the time of Roentgen's discovery of x-rays to the advent of the new method, the principles of roentgenographic recording of tissue densities have remained unchanged. First x-ray plates, and later, x-ray film have consistently proved insufficiently sensitive to the small differences in radiodensity of soft tissues to provide direct information concerning their composition. The one exception is fat, which, when aggregated, is sufficiently lower in absorption characteristics to distinguish it from other soft tissues. Excellent but necessarily limited use has been made of the naturally appearing contrast substance, air, in the thorax and abdomen.