Experimental and simulation results with the Depth-encoding Anger Detector

Abstract

Poor image quality limits clinical utility of dual-head gamma cameras for coincidence imaging. The use of thick crystals imposes one limitation. Conventional camera design results in parallax error due to an inability to measure depth-of-interaction (DOI). We are developing a modified gamma camera that measures DOI. The Depth-encoding Anger Detector incorporates a wavelength-shifting (WLS) optical fiber ribbon onto the face of an otherwise-conventional thick-crystal camera design. The conventional components compute x-y interaction coordinates and total energy signal. The WLS fiber ribbon measures DOI. We previously reported on the theoretical basis of the Depth-encoding Anger Detector and a prototype design. The diameter of a critical cone, defined by the indices of refraction of the NaI(Tl) and the WLS fibers, determines DOI. Scintillations within the cone propagate from the NaI(Tl) into the fibers; photons outside of the cone reflect back into the crystal. The Depth-encoding Anger Detector measures the cone's diameter to determine DOI. In this work, we report on simulation and experimental results from the Depth-encoding Anger Detector project. This includes the results of Detect2000 simulations used to examine different detector designs and the results of experimental measurements with the prototype system. While the simulations indicate feasibility of the concept, the simulations and experiments demonstrate that proper design and manufacture of the system are crucial for success.