Tomography

now largely restricted to IVP with linear tube motion

tube moves in opposite direction to film about a fulcrum, with blur in all but the focal plane

θ = angle of tube travel

blur width higher with θ, distance from focal plane, distance from film (magnification; object above fulcrum blurred more than one below) and orientation of tube travel

slice thickness defined for accepted amount of blurring (spatial frequency at which MTF vanishes); inversely proportional to geometric magnification and tanθ

complicated tube motions differ from shape of object examined and avoids phantom images and other artefacts

simultaneous multi-film tomography uses several layers of film exposed simultaneously (slower screens in uppermost films to ensure comparable densities) to obtain different focal planes; film spacing > plane spacing

tomosynthesis = multiple images recorded while XRT and cassette move, essentially taking different profiles that can be reconstructed to produce slices with greatly increasing blurring the further from the focal plane