EFFECTS OF ENERGY SPACE SMOOTHING AND PROJECTION SPACE NORMALIZATION ON MULTISPECTRAL PET IMAGE QUALITY

Independent processing of multispectral positron emission tomography ( MSPET) data in individual energy frames has the potential to improve s ystem sensitivity and the accuracy of energy dependent scatter correct ion. However, statistical fluctuations due to the use of multiple ener gy windows and low system detection efficiency severely undermine this potential, These limitations have been overcome without resolution lo ss by smoothing data in the energy space to suppress statistical fluct uations and by normalizing detector efficiency in the spatial domain t o minimize systematic errors. The effectiveness of these corrections w as evaluated by comparing images acquired in different energy frames w ith and without energy space smoothing. Smoothing improved the sharpne ss and contrast and decreased noise of images. The FWHM and FWTM evalu ated from line source images confirmed an earlier postulate which stat ed that smoothing in the energy space has no effect on image resolutio n since such process does not move counts across lines of response (LO Rs). It was concluded that smoothing in the energy space in conjunctio n with normalization in the projection space is a prerequisite for sub sequent energy-dependent data processing such as scatter correction.