The adaptive single-photon emission computed tomography (SPECT) system studied here acquires an initial scout image to obtain preliminary information about the object. Then the configuration is adjusted by selecting the size of the pinhole and the magnification that optimize system performance on an ensemble of virtual objects generated to be consistent with the scout data. In this study the object is a lumpy background that contains a Gaussian signal with a variable width and amplitude. The virtual objects in the ensemble are imaged by all of the available configurations and the subsequent images are evaluated with the scanning linear estimator to obtain an estimate of the signal width and amplitude. The ensemble mean squared error (EMSE) on the virtual ensemble between the estimated and the true parameters serves as the performance figure of merit for selecting the optimum configuration. The results indicate that variability in the original object background, noise and signal parameters leads to a specific optimum configuration in each case. A statistical study carried out for a number of objects show that the adaptive system on average performs better than its nonadaptive counterpart.
A folded holographic optical system is modeled for use as a building block for a compact imager. The design of the
compact imaging system allows for a thin optical configuration and reduction in the size of the optical elements. In the
folded design a transmission hologram in a slanted configuration folds the field of view of the lens and points it at a
specific direction in the object space. The slanted geometry results in a compressed non-uniform field of view that is
defined as a vignetting function and generated by a ray-tracing program. In the compact imaging system, multiple
folded holographic imagers are used in an array to extend the field of view. Each imager unit is optimized to collect a
segment of light from the object scene. The combination of imager units defines the composite field of view of the
compact imaging system. The folded holographic imager is capable of capturing an image with full-field angle of 30°.