REDUCTION OF TRUNCATION ARTIFACTS IN FAN-BEAM TRANSMISSION IMAGING USING A SPATIALLY VARYING GAMMA PRIOR

Using fan beam transmission imaging to obtain an attenuation estimate of an object for attenuation correction is limited because the object mag not be completely in the field of view of the camera at ail angles , This truncation of object data creates artifacts in the attenuation map during reconstruction which may result in problems in the attenuat ion correction of the emission image, To improve the quality of the at tenuation map, we have used information from the scatter window recons truction of projections from a parallel hole collimator on one of the heads of the SPECT system, This scatter window reconstruction is used to create a segmentation-based attenuation map of the object, We use t his map as a pixel-by-pixel gamma prior to aid in the iterative recons truction of the final attenuation map, In the fully sampled central re gion, use of the segmentation map information is unnecessary; but in t he poorly sampled, outer region, the use of the segmentation map is es sential to obtain an accurate reconstruction. We use a spatially varyi ng weight function for the gamma prior to reflect our confidence in th e transmission data in the central region while emphasizing the prior in the outer region. The result is a high-quality density map over bot h the fully sampled and poorly sampled regions, Furthermore, since the line integrals for the transmission data are preserved in the iterati ve reconstruction, the algorithm does not require precise determinatio ns of the attenuation coefficients in the segmentation maps to create an accurate attenuation map.