UC Berkeley

Compton cameras image gamma-rays in the range from hundreds of keV to several MeV and are useful for a range of applications including astrophysics, contamination remedia- tion, medical imaging and nuclear security. The data acquired from Compton cameras needs to be inverted to recover the desired gamma-ray distribution in space and energy using reconstruction algorithms. The focus of this work is the process of converting measured Compton camera interaction data into gamma-ray images via such methods. Several ap- proaches are covered, including filtered back-projection and iterative methods. This work makes advances in each of these approaches both theoretically and through demonstration measurements. Some of these methods are optimized for real-time imaging.

Working in the Applied Nuclear Physics group at Lawrence Berkeley Lab and in Nuclear Engineering at UC Berkeley provided a unique opportunity to analyze data from three different Compton cameras. This provided a cross device perspective that ultimately made the imaging algorithms developed for one system more robust for another. Having this perspective also made it more clear which factors of the image reconstruction algorithms were essential. Using these different systems, techniques are described to analyze the quality of data that can be collected from a Compton imaging system. The three imaging systems cover a variety of semiconductor materials: Si, CdZnTe and HPGe. These devices range from lab development platforms to a small compact Compton camera device. The compact device, called HEMI, was taken to Fukushima, Japan and flown on a remote control helicopter to map the cesium contamination. The results from that measurement are detailed and shown.

Another focus of this work is sensor fusion with auxiliary data sources, which include visual cameras, depth cameras, GPS and IMU sensors. This is used to expand the number of reconstruction dimensions. This also provides contextual information for the gamma- ray intensity reconstruction and can be used to overcome some limitations with gamma-ray imaging, such as inherent low count rates. This approach of sensor fusion is demonstrated with lab measurements and the measurement taken in Fukushima, Japan.