An algorithm for the simultaneous reconstruction of the radionuclide activity distribution and attenuation map based on PET scatter data

Abstract

Attenuation correction is required for both qualitative and quantitative analysis of positron emission tomography (PET) imaging. Traditional attenuation correction methods use a transmission scan, such as a computerized tomography (CT) or an external radionuclide source scan. The transmission scan contaminates the emission data of PET if the transmission scan is performed during the PET scan. When the transmission scan is performed separately, artifacts can be introduced due to patient movement. In addition, the conversion of the CT image to an attenuation map at PET energy and the smaller field-of-view (FOV) of a transmission scan cause other artifacts. For PET/MR systems, detector compatibility issues for traditional PET scanners along with image truncation and patient movements also introduce artifacts. Therefore a transmission-less attenuation correction approach is needed. Previous studies using true coincidence data to simultaneously reconstruct the attenuation map and radionuclide activity distribution suffer from the cross-talk between the distributions. In this study, the scatter data of PET was used to reconstruct the electron density distribution as a representation of the attenuation map. A simultaneous reconstruction of the activity and electron density distributions were developed. Reconstruction results have shown that the contrast recovery coefficients of the region of interests were comparable to the reconstructions using a known attenuation map.