An Improved Coded-Aperture System for Emission Computed Tomography (ECT)

The performance of an ECT system using an annular coded aperture and concentric annular detector has been studied by computer simulation. To Insure that the simulations are realistic, all appropriate geometrical factors (e.g. inverse-square attenuation) and tissue photon-interaction properties (both multiple Compton scattering and photoelectric effect) were Included. Also included was a 1% energy uncertainty to emulate solid-state detectors. The most Important features of the system were found to be that it: (1) produces highly reliable tomographic (ECT) Images of single-gamma radionuclide distributions, (2) uses a relatively large fraction of the emitted photons, about 0.2%. In the full three-dimensional Image system, also discussed, about 10% are used, (3) reconstructs pixel sizes as small a 1 mm using reasonable system design parameters, (4) uses gammas of any energy greater than about 125 keV, (5) determines the standard deviations of the activity in each pixel, thus enabling the statistical significance of any image feature to be calculated, and (6) measures absolute amounts of radioactivity.