SPECT SCATTER MODELING IN NONUNIFORM ATTENUATING OBJECTS

SPECT quantitation and image contrast are degraded by photon scatter. Water equivalent depths (WEDs) have been used by several investigators to model scatter responses in non-uniform attenuators. The drawback o f this approach is the occurrence of undesired fluctuations in the sha pe of the scatter responses, as is shown by measurements. An improveme nt of the WED method is presented, based on the assumption that only a part of the scattering object (the region in the 'scatter cone') cont ributes significantly to the detected scatter events. The remaining pa rt of the object is treated as a uniform medium. The extension of the WED method with extra-conical invariance (WEDECI) is evaluated by proj ection measurements of a phantom with a Tc-99m source. Shapes of scatt er responses predicted by the WEDECI method are found to agree better with the measurements than those predicted by conventional WEDs.