Evaluation of cassette performance: physical factors affecting patient exposure and image contrast

Physical properties of four radiographic cassettes were investigated in combination with various screen/film systems. These properties included (a) transmittance of monoenergetic x rays over 14-96 keV and comparison with predictions based on attenuation coefficients; (b) relative patient exposure from 60 to 120 kV (from phantom measurements) and correlation with predictions based on measured transmittance as well as average energies and angles of incident radiation; and (c) amounts of scatter from various cassette materials and comparison with Monte Carlo calculations. The results provide a model of performance based on quantitation of cassette effects on system speed and image contrast. Carbon-fiber cassettes required the lowest patient exposure, produced the least scatter, and (in low-scatter situations) were capable of increased image contrast.