Abstract
The Voxel Imaging PET (VIP) Pathfinder project intends to show the advantages of using pixelated semiconductor technology for nuclear medicine applications to achieve an improved image reconstruction without efficiency loss. It proposes designs for Positron Emission Tomography (PET), Positron Emission Mammography (PEM) and Compton gamma camera detectors with a large number of signal channels (of the order of 106). The design is based on the use of a pixelated CdTe Schottky detector to have optimal energy and spatial resolution. An individual read-out channel is dedicated for each detector voxel of size 1 × 1 × 2 mm3 using an application-specific integrated circuit (ASIC) which the VIP project has designed, developed and is currently evaluating experimentally.The behaviour of the signal charge carriers in CdTe should be wellunderstood because it has an impact on the performance of the readoutchannels. For this purpose the Finite Element Method (FEM)Multiphysics COMSOL software package has been used to simulate thebehaviour of signal charge carriers in CdTe and extract values for theexpected charge sharing depending on the impact point and biasvoltage. The results on charge sharing obtained with COMSOL arecombined with GAMOS, a Geant based particle tracking Monte Carlosoftware package, to get a full evaluation of the amount of chargesharing in pixelated CdTe for different gamma impact points.
Highlights
IntroductionUsing finely segmented CdTe allowing for precise precision measurement of the gamma impact point with an excellent energy resolution of about 1% at 511 keV [2]
The Voxel Imaging Positron Emission Tomography (PET) (VIP) Pathfinder project1 aims to show that the VIP design for PET [1] allows for better image reconstruction because of the excellent spatial and energy resolution it can provide, compared to state-of-the-art crystal PETs
Following the example of other experiments (e.g. [3,4,5]), we used a tracking program (the Geant4-based Architecture for Medicine-Oriented Simulations (GAMOS) software [6]) to estimate the size of the initial charge carrier cloud and, subsequently, the finite element methods (FEM) software package COMSOL [7] to numerically calculate the behaviour of the charge carriers in the detector and the resulting charge induction
Summary
Using finely segmented CdTe allowing for precise precision measurement of the gamma impact point with an excellent energy resolution of about 1% at 511 keV [2]. The drawback of small pixel sizes is that a large fraction of photons have energy depositions in more than one neighbouring pixels. To correct for this, either charge sharing correction algorithms should be studied or the charge sharing events should be rejected, so it is important to know the amount of charge sharing events. [3,4,5]), we used a tracking program (the Geant4-based Architecture for Medicine-Oriented Simulations (GAMOS) software [6]) to estimate the size of the initial charge carrier cloud and, subsequently, the finite element methods (FEM) software package COMSOL [7] to numerically calculate the behaviour of the charge carriers in the detector and the resulting charge induction. The convolution of the results from these programs gives an estimate of the total amount of charge sharing
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