Reconstruction Of Object-specific Attenuation Map For Quantitative SPECT

A method to improve the reconstruction of objectspecific attenuation maps for accurate quantification of single-photon emission computed tomography (SPECT) was studied. This method aims to (1) utilize the a priori known attenuation coefkients and (2) compensate for the fan-beam truncation of transmission scans in reconstructing the attenuation map. An external radioactive line source was simulated to generate the fan-beam transmission data through a thorax phantom using a single detector of three-headed SPECT configuration. More than half of the 120 projections distributed evenly over 360 degrees were truncated. The thorax phantom had a size of 1282 array. Emission data was computer synthesized, following the transmission simulation, using two parallel-beam collimated detectors of the SPECT configuration. The simulated emission data was attenuated by the thorax phantom. The transmission data was reconstructed by an iterative maximum aposteriori probability algorithm which simultaneously segments the reconstructed attenuation map with the a priori known attenuation coefficients of bone, lung, soft tissues, and air. The truncation was compensated in the forward projection by estimating the truncated data The continuity of the estimated data to the simulated data was considered in the backprojection. The truncation-compensated and segmented attenuation map was used to reconstruct the emission data. Significant improvement (> 5%) in quantification of SPECT was achieved, as compared to the reconstruction using the truncated attenuation map.