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

To optimize both spatial resolution and detection efficiency in brain single photon emission computed tomography (SPECT) imaging using a rectangular camera, an asymmetric double-focal cone-beam collimator is proposed. To fit the patient´s entire head into the field-of-view of the collimator with dimensions of 50 cm×40 cm and at 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 produced by the Feldkamp algorithm are more severe compared to those in a symmetric cone-beam geometry. To improve the reconstructed image quality, a fully three-dimensional reconstruction algorithm is extended to the asymmetric double-focal cone-beam geometry. The algorithm involves nonstationary 2-D filtering and a reprojection technique for estimation of the missing data caused by a single-orbit cone-beam geometry. The results from simulation studies with the 3-D Defrise slab phantom demonstrate that the fully 3-D algorithm provides a much improved image quality in terms of reduced slice-to-slice crosstalk and shape elongation compared to that produced by the conventional Feldkamp algorithm