Two-dimensional filtering of SPECT images using the Metz and Wiener filters

Two-dimensional filtering, both before and after reconstruction, has been applied to the processing of single photon emission computerized tomographic (SPECT) images. The filters investigated were the count-dependent Metz filter and Wiener filter, both of which automatically adapt to the image being processed. Using a SPECT phantom, with images reconstructed with these filters rather than the ramp, we observed a statistically significant increase (p less than 0.05) in the image contrast for solid Plexiglas spheres, and significant decrease (p less than 0.05) in the percent fractional standard deviation of counts in a region of uniform activity. The adaptability of these filters is demonstrated by a comparison of SPECT acquisitions of the phantom at two different count levels. An example of their application to clinical studies is presented. We conclude that two-dimensional digital image restoration with these techniques can produce a significant increase in SPECT image quality, with a small cost in processing time when these techniques are implemented on an array processor.