Implementation of a body-contour orbit on a microprocessor-controlled gantry

For single-photon-emission CT, body-counter orbits minimize the gap between patient and detector. The optimal orbit is peanut shaped: R = (b2sin2θ + a2cos2θ)12/, where R is the orbit radius. An approximation to this orbit has been implemented on a microprocessors system dedicated to gantry motion control (Picker SX300): R = b + (a - b)[sinθ] + z, where z is a safety correction factor for the tomographic table. For a typical patient, this orbit transcribes an area 34% less than that of a circular orbit. With a centered line source (26-cm-diameter water-filled cylinder), the contour orbit (34 X 56 cm) full width at half maximum resolution was 16.6 mm compared with 20.6 mm from a circular orbit (56-cm diameter)