EFFECTS OF TOMOGRAPHIC MOTION, SLICE THICKNESS, AND OBJECT THICKNESS ON FILM DENSITY

The experiment used the computer-aided CommCat model IS 2000 tomograph ic machine (Imaging Sciences International, Roebling, N.J.). The objec tive of the experiment was to study the influence of tomographic tube motion, tomographic slice thickness, and object thickness on film dens ity. The experiment was conducted by x-radiating an aluminum step-wedg e placed along the x-axis. Exposures were made for different tube moti ons and for different slice thicknesses. In linear horizontal and line ar vertical motions, an increased slice thickness decreased film densi ty. Slice thickness had a stronger effect on film density when the obj ect to be x-radiated was thinner. In circular, elliptical, spiral, and hypocycloidal motions, changes in slice thickness had no noticeable e ffect on film density because the manufacturer had programmed the mach ine to produce approximately similar exposure times by increasing the x-ray tube velocity with increases in the angular magnitude of the tom ographic are. The only effect was that of object thickness. Object thi ckness had a greater effect on film density for circular, elliptical, spiral, and hypocycloidal tube motions than for linear horizontal and linear vertical tube motions. Clinical observation showed that except for the linear vertical motion (motion that was oriented in the same d irection as that of the tube travel) all other motions produced a zone of diffusion along the edges of the steps of the step-wedge. An incre ase in slice thickness decreased the width of the zone of diffusion. I n summation, tube motion, slice thickness, and object thickness had an effect on film density. Slice thickness had a noticeable effect on fi lm density in linear but not in multidirectional tomography. Object th ickness had a greater effect on film density in multidirectional than in linear tomography.