Search

Options for optimizing the energy and spatial resolution of gamma-ray imaging detectors based on thick, monolithic crystals shaped like fiat-topped pyramids were studied. Monte Carlo simulations were made of the scintillation light transport for evaluating the effect of four parameters on the energy resolution, the spatial resolutions, and the depth of interaction (DOI) resolution of the gamma-ray imaging detector. These four parameters are: the reflectivity of the surface coating; the scatter mean free path; the absorption mean free path of the scintillation light; and the angle that defines the inclination of the sides of the pyramidal frustum. In real detectors, the values for the mean free paths for optical photons are normally not known. We estimated these by comparing MC simulations of detector resolutions to measurements for three gamma-ray imaging detectors with LYSO and LSO from different suppliers and with different surface coatings and geometries. The gamma-ray imaging detector measures the energy, centroids, and depth of interaction of the gamma-ray. DOI enhanced charge dividing readouts were used to measure the depth of interaction. Index Terms--Crystal geometry, gamma ray imaging, interaction depth, monolithic scintillator, surface coating.

Digital Positron Emission Tomography (PET) systems enable us to implement sophisticated algorithms for real time signal processing. Usually, energy and position are encoded on the amplitude of the digitized signals. Although a lot of work has been made for spectroscopy applications, digital pulse height estimation in PET detectors presents important challenges mainly due to the fast response of state-of-the-art detectors. In this paper we propose a digital filtering technique for improving amplitude estimation in order to achieve high spatial and energy resolution with moderate conversion rates ( Index Terms--Adaptive signal processing, biomedical nuclear imaging, FIR digital filters, least mean square (LMS) methods, positron emission tomography (PET).

An ASIC front-end has been developed for multianode photomultiplier based nuclear imaging devices. Its architecture has been designed to improve resolution and decrease pile-up probability in Positron Emission Tomography systems which employ continuous scintillator crystals. Analog computation elements are isolated from the photomultiplier by means of a current sensitive preamplifier stage. This allows digitally programmable adjustment of every anode gain, also providing better resolution in gamma event position calculation and a shorter front-end deadtime. The preamplifier stage also offers the possibility of using other types of photomultiplier devices such as SiPM. The ASIC architecture includes measurement of the depth of interaction of the gamma event based on the width of the light distribution in order to reduce parallax error and increase spatial resolution during image reconstruction stage. An output stage of transresistance amplifiers offer voltage output signals which may be introduced in the A/D conversion stage with no further processing. Index Terms--ASIC, depth of interaction, front-end, PET, pile-up.