An investigation of the magnitude and causes of count loss artifacts in SPECT imaging.

A quantitative evaluation and an investigation of the mechanism of the count losses that can occur in SPECT imaging is described. The most common clinical example of the artifacts which result from this is encountered when sections are taken through the femoral heads in skeletal studies of the pelvis. From some simple phantom studies, it was identified that the count losses were associated with the presence of a high dynamic range in the projection data. Further information was obtained from simulation studies. It was found that the count loss phenomenon is caused by the combined effects of the presence of a high count density area and a structure with a relatively high attenuation level. An appreciation of the presence, magnitude, and mechanism of this effect is important if erroneous clinical findings are to be avoided. This is particularly relevant because of the existence of a variety of techniques that can be used to remove the resulting artifacts.