New digital processor for SPECT camera-correction of multiple-energy photon spatial distortion

Spatial distortion of a SPECT image is energy dependent, due to the discrete nature of the photomultiplier tube (PMT) array and non-uniform response of a PMT to the event location and different depth of interaction in the crystal with different photon energy. A spatial distortion correction without consideration of different photon energies can not produce a satisfactory result for different type tracers used in imaging, especially multiple radionuclide imaging. A new digital processor developed by Trionix makes the correction of spatial distortion independent of energy. The new processor digitizes and computes the photon location distortion according to its energy, and the correction is automatically applied to on-line data acquisition. The correction of multiple-energy photon spatial distortion effectively improves the accuracy of the camera detecting system as well as the camera imaging capability with an expanded photon energy range from 50 to 560 keV. The multiple window spatial registration of the detector at the edges of useful field of view is improved from 2.5 mm to 0.4 mm by using a Ga-67 source. No obvious difference can be observed using Tc-99m, In-111 or Ga-67 isotopes, as judged from the images of the four section resolution bar and the Jaszczak phantom.