Transmission image reconstruction and redundant information in SPECT with asymmetric fanbeam collimation

Two novel approaches for the reconstruction of asymmetric fanbeam transmission computed tomography data are introduced. The first approach, called the hybrid approach, involves a Fourier-based rebinning of the fanbeam data into parallel-beam data. Reconstruction then proceeds by use of filtered backprojection (FBP). The second approach, called generalized fanbeam filtered backprojection (GFFBP), involves direct fanbeam FBP reconstruction of a modified fanbeam sinogram. In both cases; the data are multiplied by weight functions that seek to appropriately normalize redundant data while exploiting them for noise reduction. The hybrid approach is seen to lead to lower noise levels than is the GFFBP approach, although this comes at the expense of slightly degraded image resolution. The principal source of the GFFBP´s higher noise levels-the distance-dependent fanbeam backprojection factor-also produces high-intensity peripheral artifacts that can impinge upon the objects of interest. Because it ultimately makes use of parallel-beam FBP for reconstruction, the hybrid approach avoids this fanbeam factor and the peripheral artifacts