Reconstruction Methods for Quantitative Brain SPECT

We have studied reconstruction methods currently available for use in quantitative brain SPECT imaging. The conventional reconstruction methods are based on the filtered backprojection algorithm. Assuming uniform attenuation, the Chang algorithm is effective in attenuation compensation. The collimator response can be compensated for by restoration filter with an average collimator response function. Scatter compensation can be achieved by the dual window subtraction method or by incorporating an average scatter response function in the restoration filter. The dual window subtraction method is an approximate but efficient means of providing scatter compensated projection data. Iteration reconstruction method can be applied to these data for addition compensation for attenuation and the spatially variant collimator response. The latter is accomplished by incorporating the exact model of attenuation and detector response function in the projector / backprojector of the iterative algorithm. A three-dimensional brain phantom was used in the evaluation study. Projection data were collected into the photopeak and a lower scatter energy windows for scatter compensation. The images obtained from various reconstruction methods were compared for quantitative accuracy with respect to the known 3D phantom activity distribution.