Improved image quality from asymmetric double-focal cone-beam SPECT

To optimize both spatial resolution and detection efficiency in brain SPECT (single photon emission computed tomography) imaging using a rectangular camera, an asymmetric double-focal cone-beam collimator is proposed with the focal points located near the base of the patient´s head. To fit the entire head into the field-of-view of the detector (50 cm×40 cm) for a radius-of-rotation of 15 cm, the focal lengths of the collimator are 55 and 70 cm, respectively, in the transverse and axial directions. With this geometry, the artifacts in the reconstructed image become more severe due to the larger vertex angle between the top of the head and the central plane compared to that in a symmetric cone-beam geometry. To improve the reconstructed image quality, a fully 3-D reconstruction algorithm which involves a nonstationary 2-D filtering and a reprojection technique for estimation of the missing data caused by a single-orbit cone-beam geometry are implemented. The results from simulation studies with the 3-D Defrise slab phantom demonstrated that, by using the full 3-D algorithm and the reprojection technique, the reconstructed image quality was significantly improved in terms of reduced slice-to-slice cross talks and shape elongation compared to that produced by the conventional Feldkamp algorithm