According to findings of the WHO (World Health Organisation), the two major causes of death in the EUROPEAN UNION are cardio-vascular diseases (CVD) and cancer, accounting for 50% and 20% of all deaths in 2002, respectively. With the increase in life expectancy, the costs that society will spend on medical care are expected to rise above 10% of the gross national product of Western Europe in the near future. This indicates an increasing need for diagnostic tools in oncology and cardiology. In both fields, positron emission tomography (PET) has emerged as one of the imaging techniques of choice for diagnosis, staging, therapy monitoring and recurrence assessment. Earlier diagnosis allows more efficient therapy, which improves the quality of life of the patients, and reduces medical costs.
The objective of the project is to improve the performance of PET detectors. Since PET is a medical imaging modality, improvement must mean additional value for the patient and the physician, and for an imaging modality, this means better image quality. For PET, higher spatial resolution and higher image contrast are desirable for increasing the diagnostic value of the images, and thus improving the therapy outcome for the patient. By improving the sensitivity of PET detectors, the project also aims to significantly reduce scan times, minimising patient discomfort and resulting in increased efficiency of the clinical work flow.
In PET, the patient is administered a radiopharmaceutical, and the quality of the PET images is primarily limited by the performance of the detectors which capture the radiation emitted from the patient. Thus, higher spatial resolution and contrast in the image essentially means detectors with higher intrinsic resolution detectors which allow for measuring the position of the emission in the body with higher precision. Due to the PET principle, this requires good spatial and time resolution. The latter is reflected in the concept of time-of-flight (TOF) PET.
The two fundamental components of current PET detectors are scintillator crystals and photomultiplier tubes (PMTs). Incremental improvements of the detectors have been achieved by minor changes to this design - smaller crystals improve the spatial resolution, faster PMTs the timing. This project aims at substantial improvements: new scintillation materials, a novel design, and position-sensitive semiconductor light sensors instead of PMTs.
The combination of new scintillation materials and fast, position-sensitive semiconductor light sensors is expected to enable the development of monolithic PET detectors with significantly improved performance compared to current technology. Such detectors would offer better spatial resolution, time-of-flight capability, better energy resolution, and higher sensitivity, and they would be economically attractive. To turn this promise into reality, research on several issues is needed. These will be addressed by this project.
By the end of the project, there will be a prototype detector that demonstrates the performance potential of the novel concept. The performance of a full PET scanner based on the new design will be predicted based on the results obtained in this project, and insight will have been gained into both options and limitations that the design imposes on future products.
Keywords: PET (Positron Emission Tomography) detector, Si photomultiplier, molecular imaging.