Performance of electronically collimated SPECT imaging system in the energy range from 140 keV to 511 keV

Conventional SPECT cameras rely on photon-absorbing collimators to collect spatial information on radioactive source distributions thereby coupling efficiency with spatial resolution in an inverse relationship as well as causing a rapid decrease in performance with increasing incident photon energy. The Compton SPECT imaging technique replaces the conventional collimator with a position sensitive scattering detector, or “electronic” collimator. This decouples the efficiency and spatial resolution of the system and also leads to increased performance for higher energy sources. However, new technical challenges are introduced in the form of high count rates, timing resolution requirements, and complexity in the image reconstruction. A prototype system using pixelated silicon as the position sensitive scattering detector has been built to quantify the benefits realized by a Compton camera for higher energy sources in the range from ^99mTc (140 keV) to the positron annihilation energy (511 keV). In order to reduce some of the technical complexities of the conventional Compton camera arrangement, the initial prototype has been configured to effectively limit the image region to a two-dimensional “slice” geometry.