Resumen de Study of a High-Resolution PET System Using a Silicon Detector Probe
Karol Brzezinski
Clinical positron emission tomography (PET) is a medical imaging modality that provides three-dimensional information about the distribution of a tracer substance in a patient's body. Tracers are designed to follow specific metabolic pathways, giving PET the capability to provide functional rather than structural information. Although offering information complementary to that obtained using computed tomography (CT) and magnetic resonance imaging (MRI), clinical PET has a relatively low spatial resolution when compared to these other imaging modalities. There are practical limits on resolution in modern clinical scanners which utilize the standard PET ring geometry. The use of high-resolution detectors, added within the scanner's field of view (FOV), has been proposed as a method of increasing the resolution of PET images. The “PET-probe'” geometry is a case where one (or a stack of multiple) such detector(s) is placed close to a region of interest where higher resolution is desired. This work explores such a system, using a modern clinical PET scanner in coincidence with a probe consisting of a stack of Silicon detectors. The studies presented in the thesis quantify the improvement brought about by the probe and suggest a clinical application for the device. The system is studied at two levels: first, using Monte Carlo simulations of the system and second, by obtaining preliminary results from an experimental prototype. The chapters of the thesis are grouped into five parts. The first part overviews the PET imaging technique and the PET probe principle before going into the details of the specific system on which this work is focused. The second part presents preparatory simulation studies of the system characteristics: an examination of event types is used to explore the effect of time and energy settings, and a study of the characteristics of the probe data is used to develop appropriate image reconstruction software. Further simulation studies, performed to characterize the capabilities of the probe system, are presented in part three. These studies quantify the improvement in image quality provided by the probe system with respect to that of the scanner alone. Any enhancement to the final image is expected to be localized, and therefore was studied as it varies over the FOV. The studies address image quality in terms of spatial resolution, contrast and spill-over ratio. In order to demonstrate the applicability of the system to PET mammography (PETM), simulations were conducted using a phantom which mimics a breast imaging scenario. In this context, lesion detectability was quantified in terms of contrast-to-noise ratio. Although the thesis focuses on breast imaging, the proposed system could be used in other applications where high spatial resolution is desired in a determined region of interest. The fourth part of the thesis consists of studies performed using an experimental prototype of the PET probe system. Due to the preliminary nature of these studies they are not included in the main body of the work, but rather are presented as a supplement. The experimental studies present proof-of-concept support for the proposed system, while the experimental prototype acted as a physical testbed for the data processing and image reconstruction software developed within the dissertation. In the fifth part of this work, conclusions are presented as well as prospects for future investigation of the PET probe system.
