Body-and-lungs-outline penalized-likelihood recon-struction of asymmetric cone-beam transmission data acquired with less than complete gantry rotation

Abstract

Background: Ideally a 360-degree acquisition is preferred to avoid truncation with asymmetric cone-beam transmission imaging. However, a 360-degree gantry rotation may not be allowed on some SPECT imaging systems, especially those dedicated to cardiac imaging. The objective of this study was to investigate the feasibility of incorporating the body-and-lungs outline from emission data in penalized likelihood reconstruction with transmission projections acquired over less than complete gantry rotation. Methods: SPECT (Tc99m) emission and sequential transmission data were acquired in list-mode with IRIX SPECT system of the Data Spectrum Anthropomorphic phantom with cardiac insert. The transmission data were acquired using the modified Beacon approach using stationary Ba-133 point sources with 360-degree rotation at 60 angular steps. A three-dimensional mask which approximates the outline of body and lungs was first generated by smoothing, thresholding, and scaling a preliminary emission image and then added to the log-likelihood as an additional quadratic penalty term, which serves to reduce the attenuation coefficient in the blackened regions on the mask. Attenuation-maps were reconstructed for 360, 312, 270, 228, and 180 degree gantry-rotations, respectively, using the Separable Paraboloidal Surrogates algorithm, with and without the additional penalty term. Results: Attenuation maps reconstructed with the prior from the emission image showed reduced truncation of the right lung. Conclusion: Prior information from emission image helps reduce the truncation of attenuation map acquired by limited gantry rotation.