Radiography with heavy particles

The failure of x-ray diagnostic techniques to accurately detect tumors and other regions of abnormal density in soft tissue has been, for many years, a significant shortcoming of this important technique in medicine. Accelerated heavy particles with plastics for track detection can be used to record small differences in density in soft tissues which may correspond to biological structures and abnormalities. In heavy-particle radiography (HPR), plastic detectors are well suited for recording images since their threshold nature makes them insensitive to spurious low-LET radiations and light secondaries. Sources of error which limit the resolution of HPR are inversely dependent on the atomic mass number (A) of the incident particle. Range straggling, responsible for loss of depth resolution, is proportional to A$sup -$ $sub 0$ $sup 5$ while multiple scattering which degrades lateral resolution is approximately proportional to A$sup -0$.$sup 395$. Recent experiments showing calcification in human blood vessels and soft tissue features in rats underline the potential of HPR as a diagnostic tool. High-resolution, three-dimensional reconstructions are possible using multiple layer plastic detectors and the short exposure time produces blur- free radiographs of specimens whose internal structure may be in motion. (auth)