Infographics / X-ray Physics

Conventional (linear) tomography

The x-ray tube and cassette are rigidly linked and pivot about a fixed fulcrum, moving in opposite directions during the exposure. A point in the focal (fulcrum) plane projects to the same point on the film in every tube position, so it stays sharp, while a structure above or below that plane projects to different points and is blurred. The swing (tomographic) angle at the fulcrum sets the slice thickness: a larger angle gives more off-plane blur and a thinner section.

Conventional (linear) tomography geometry The x-ray tube and cassette are rigidly linked and pivot about a fixed fulcrum, moving in opposite directions during the exposure. A point in the focal (fulcrum) plane projects to the same point on the film in every tube position, so it stays sharp, while a structure above or below that plane projects to different points and is blurred. The swing (tomographic) angle at the fulcrum sets the slice thickness: a larger angle gives more off-plane blur and a thinner section. focal (fulcrum) plane structures here stay in focus tube travel tube, t1 tube, t2 θ off-plane structure cassette, t1 cassette, t2 same film point → sharp blur blur cassette travel (opposite) focal-plane point registers to one film spot → stays sharp off-plane point spreads across film → blurred θ = swing (tomographic) angle; larger θ → thinner section tube and cassette move in opposite directions about the fulcrum
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