THE SPATIALLY-VARIANT BACKPROJECTION POINT KERNEL FUNCTION OF AN ENERGY-SUBTRACTION COMPTON SCATTER CAMERA FOR MEDICAL IMAGING

An energy-subtraction Compton scatter camera (ESCSC) was previously pr oposed for in-vivo imaging of radiopharmaceuticals used as bio-tracers in Nuclear Medicine. To further evaluate the usefulness of this ESCSC design, studies pertaining to image reconstruction are explored and p resented. Generally speaking, a Compton scatter camera works on the pr inciple that an emitted gamma ray undergoes a Compton scatter interact ion in a primary detector system and then is subsequently absorbed by a secondary detector system. I Using the measured interaction energies and positions, a cone surface can be backprojected which intercepts t he emission space near the point of the gamma-ray emission (proximity depends on resolution). When backprojecting and linearly superposing m ultiple cones into a source space, calculations should include normali zing the total weight contributed by each cone as well as how the diff erentially intercepted area increases as you move farther away from th e vertex of the cone (i.e., intercepted voxels farther away from the v ertex are given less weight). Backprojected ''point kernel profiles'', based upon simulated data, are presented corresponding to point sourc es located at several positions (revealing the degree of spatial varia nce) within the ESCSC camera geometry. From these results the spatiall y variant point kernel function may be deduced for future use in image reconstruction. Additionally, two different algorithms for backprojec tion are compared.