3-DIMENSIONAL RESTORATION OF SINGLE-PHOTON EMISSION COMPUTED-TOMOGRAPHY IMAGES

Restoration of single photon emission computed tomography (SPECT) imag es is usually performed either on two-dimensional (2-D) projection ima ges (pre-reconstruction restoration) or on SPECT slices (post-reconstr uction restoration). This study presents the application of a three-di mensional (3-D) filter in restoring SPECT images. The 3-D filter is sh own to perform better than the 2-D methods because it takes into consi deration the interslice information in the filtering process and has a relatively space-invariant blur function. To reduce the space-varianc e of the 3-D point spread function (PSF), conjugate projections were c ombined by geometric averaging before reconstruction. We investigated the potential of 3-D Wiener and power spectrum equalization (PSE) filt ers. These filters were applied to SPECT images of a resolution phanto m and a large, truncated cone phantom containing two types of cold spo ts: a sphere, and a triangular prism. The filters were also applied to clinical images of the liver and spleen. The images were acquired on an ADAC GENESYS camera. A comparison was performed between results obt ained in this study and those obtained by 2-D pre-reconstruction resto ration and 2-D post-reconstruction restoration filters. Quantitative a nalysis of the 3-D restored images performed through measurement of ro ot mean squared (RMS) errors and contrast ratios showed a considerable reduction in error and increase in contrast over images restored usin g the two other methods.