Study of a Positron Emission Mammograph

Today breast cancer is among the most common causes of death for women. One in eight women will develop a tumour in her breast at least once in her lifetime. An early detection of the cancer is crucial to the patient's survival and recovery. For early detec- tion it is necessary to have an instrument with high spatial resolution and efficiency. The scope of this thesis is two aspects of a dedicated PET scanner for mammography developed by the Crystal Clear Collaboration, the ClearPEM. The first half of the thesis deals with the experimental work on scintillation crystals which constitute the main part of the detector. The second part looks into the design of the whole system and the possibility of future enhancements by adding an ultrasound probe and /or a veto-counter. The effects of these changes are studied by employing simulation tools. The key to excellent detector performance is to use scintillation crystals with properties best matched to the requirements of a given application. To better understand the scintillation characteristics of the crystals, how they are influenced by their production history and how to improve their properties, this study compares scintillation materials of three producers in respect to light yield, decay time and transmission characteristics. The non-proportional response to different photon energies and the intrinsic energy resolution of the scintillation crystals is also studied. In addition to the already mentioned properties scintillation crystals for the ClearPEM detector have to be able to resolve the position of the interaction of the photon in the crystal with high precision. Two different scintillation materials are studied with the ob jective of reaching the necessary depth of interaction resolution. The influence of the surface condition on the depth of interaction resolution is also examined. Two ma jor constraints exist in PET imaging. A PET image shows only the metabolism of the cells in the patient, no morphological information can be obtained. For this purpose an ultrasound probe is going to be integrated into the ClearPEM system. The second issue is organ activity, which is especially relevant in breast imaging because of the closeness of the region of interest to the heart. This is the main source for random coincidences. A veto counter on the patient's back is proposed to reduce the random coincidence rate. A series of Monte Carlo simulations was performed which show the negative and positive changes in sensitivity caused by changes in the scanner geometry necessary to implement the ultrasound probe and random background reduction with the veto-counter.