Comparison of three boundary detection methods for SPECT using Compton scattered photons.

Three simple methods of defining the boundary of a transverse section in single photon emission computed tomography (SPECT) were compared using Compton scattered photons from a small 99mTc source located either inside or outside a water-filled cylinder of 22 cm diameter. Scattered events were acquired with 360-degree rotation of the gamma camera and transverse section images were reconstructed using a filtered backprojection method. The boundary of section images obtained with three different geometric arrangements of the source and the camera were compared. The 90-degree Compton scatter method, using a source external to the cylinder and at 90 degrees to the front of the detector, was found to give the best boundary definition. Similarly, detection of scattered events using a radionuclide source placed outside a human body was capable of providing good boundary information for the large stack of contiguous section images produced by a rotating SPECT camera. Calculations confirmed the profound influence of boundary errors on SPECT quantitations.