We report on the first demonstration of electron-tracking based Compton-scatter gamma-ray imaging in a solid-state detector. Employing a high-resolution and fully depleted charge coupled device (CCD) we were able to measure the initial direction of the Compton-scattered electron enabling the reconstruction of the incident direction of a gamma-ray on an event-by-event basis. The scatter direction was deduced by analyzing the electron energy loss measured on the pixilated readout plane. Employing a 650μm thick Si-based CCD with 10.5μm pixel size, the measured energy loss was not only used to deduce the electron-scatter angle in the pixel plane but also in the angle perpendicular and out of the pixel plane. The latter was accomplished by relating the measured energy loss to a calculated energy loss, which is predicted using the measured energy per pixel. Combining the Compton-scatter information obtained in the CCD detector with the energy and three-dimensional position information of the scattered gamma-ray measured in a Ge detector in double-sided strip configuration, we were able to reconstruct the incident direction of the gamma-ray. This measurement demonstrates the feasibility of using Si-based devices to enable electron-tracking based Compton imaging and promises significantly increased sensitivity over conventional Compton imaging instruments or gas-based imagers, which lack in overall detection sensitivity due to the low density.

We have implemented benchmarked models to determine the gain in sensitivity of electron-tracking based Compton imaging relative to conventional Compton imaging by the use of high-resolution scientific charge-coupled devices (CCD). These models are based on the recently demonstrated ability of electron-tracking based Compton imaging by using fully depleted scientific CCDs. Here we evaluate the gain in sensitivity by employing Monte Carlo simulations in combination with advanced charge transport models to calculate two-dimensional charge distributions corresponding to experimentally obtained tracks. In order to reconstruct the angle of the incident γ-ray, a trajectory determination algorithm was used on each track and integrated into a back-projection routine utilizing a geodesic-vertex ray tracing technique. Analysis was performed for incident γ-ray energies of 662keV and results show an increase in sensitivity consistent with tracking of the Compton electron to approximately ±30°.