Optimization of the performance of a pixellated germanium Compton camera

• Main Author: Ghoggali, W.
• Published: University College London (University of London) 2015
• Subjects: 610
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639596

A planar HPGe Compton camera for nuclear medicine applications that contains 177 pixels of 4 × 4mm2, of which 25 are at the back detector, is being used to image point sources of Cs137, line sources and clinical-like shape distributed sources. Experimental results are obtained to study the e ffects of energy resolution, position sensitivity, and reconstruction algorithms on camera images. Preamplifi ed pulses are digitized for pulse shape analysis using gamma ray tracking GRT4s data acquisition cards to improve camera performance. Pulse shape analysis includes improving energy resolution of the camera, improving position sensitivity of the camera by using induced charges in neighboring pixels and implementing time coincidence algorithms to select good events. The energy resolution e ffects will be presented for three di fferent energy resolutions at 662 keV; 1.4% by implementing a basic pulse height algorithm, 0.7% with a curve fitting algorithm and 0.3% by implementing the moving window deconvolution algorithm (MWD). By improving the position sensitivity from 2.5mm to 1.25mm, an improvement of 24% in spatial resolution is expected where the currentspatial resolution of a point source 5cm from the camera is 8mm. The results show that the e ects of energy resolution are less important for this camera. Images are reconstructed using back-projection and ITEM (Imaginary Time Expectation Maximization) algorithms. Eff ects of scattering materials on embedded sources are studied. Diff erent source distributions have been studied including point sources, line sources and clinical simulations (baby-heart-like distributed sources).