Characterisation of a clover detector - For the development of a compton camera

Gamma-ray imaging techniques, such as Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT), are becoming increasingly important for clinical diagnosis. As the power of these methods becomes more evident, the use of these techniques is becoming more widespread. However, the performance of existing systems is restricted by the inherent properties of the scintillator detectors they are based on (e.g. poor energy resolution). The development of High Purity Germanium detectors has now reached the stage where they can be used as effective imaging devices. The electrical segmentation of the Germanium crystal coupled with digital signal processing electronics allows the measurement of energy, time, and position following the interaction of a gamma-ray. We propose to build a PET imaging system composed of two segmented planar HPGe detectors. The position and energy information are extracted following the digitisation of the detector charge signal, analysed using Pulse Shape Analysis (PSA) algorithms. Such a technique can potentially give a position resolution of about 1 mm(3) inside the detector volume. A prototype of a Compton camera has been built in order to test our pulse processing techniques and develop some gamma-ray tracking algorithms. The system is composed of a planar detector with 5mm strips in a 24x12 configuration, and a 16 segment coaxial Clover detector. Before being able to reconstruct the path of gamma-rays with the camera, it is necessary to calibrate the response of each detector as a function of the position. Several characterisation measurements have been made using an automated detector scanning systems. Preliminary results from the characterisation of the Clover will are presented in this paper.