Nonuniform attenuation correction in SPECT was attempted to improve quantitative SPECT evaluation. Attenuation-coefficient maps required for the correction were obtained from X-ray CT image data. Two methods were used for the correction. One was Singh's method which was proposed for nonuniform attenuation correction. The other was Chang's method which was modified for nonuniform attenuation correction in the present work.
The properties of the Singh method were studied by co mputer experiments for nonuniform mathematical phantoms and were compared with those of the modified Chang method. The two methods produced similar correction results.
Problems in clinical applications o f attenuation correction using XCT data were studied. Three major problems were found: the determination of average energy of X-rays used to take XCT images, the effect of scattered photons, and the registration of anatomical positions between XCT image and the corresponding uncorrected SPECT image. Further study will be necessary to solve the problems.
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