Non-circular orbits for the reduction of uniformity artefacts in SPECT

A severe problem in single photon emission computerised tomography (SPECT) is the production of artefacts resulting from variations of uniformity in systems such as those using rotating gamma cameras. While non-circular orbits, or rather elliptical orbits, have been tried by a few workers with the aim of approaching closer to the patient, and thus improving resolution (e.g. Gottschalk and Salem, 1982), the value of such orbits in reducing artefacts seems to have gone largely unpublished. A new simple technique is here presented that is applicable to almost any system to generate non-circular orbits primarily with a view to reducing the effect of non-uniformity in producing tomographic artefacts. It should be of particular value with older rotating gamma camera systems having poor uniformity.