Euromedim 2006 :1st European Conference on Molecular Imaging Technology

CdZnTe Detectors for the Positron Emission Tomographic Imaging of Small Animals

11 May 2006, 14:00

1h

Palais du Pharo, Marseille

poster • Status of animal and clinical PET, SPECT and CT (biomedical and technical) Poster session : Imaging systems, Molecular Imaging

Speaker

Dr LOICK VERGER (CEA-LETI)

Description

We propose here is to study the suitability of a new solid state detector like cadmium telluride (CdTe and CdZnTe) detectors to address the spatial resolution issue associated with small animal Positron Emission Tomography (PET) systems. The main advantage of semi-conducting detectors over scintillation detectors lies in the fact that the segmentation can be obtained very easily thanks to the electrode pixellisation as small as desired. We have jointly developed a specific three-dimensional CdZnTe (CZT) detector geometry (16x20x0.9 mm3 CZT detectors equipped with specific orthogonal strips including 16 anodes and 5 cathodes with 1 and 4 mm pitch respectively) for a transverse irradiation and a preamplifier stage to achieve the best coincidence timing performance between two CZT detectors. The encouraging CZT-CZT coincidence time of 2.6ns FWHM obtained with planar detector has been confirmed with orthogonal strips CZT-BaF2 coincidence measurements. In a second step, we simulate the spatial resolution and detection efficiency performance of a realistic stacked CZT detector module with depth of interaction (DOI) capability. Preliminary simulations indicate that the proposed design could outperform an LSO-based system, with a better homogeneity of the spatial resolution across the Field Of View (<1 mm FWHM up to 44 mm off the FOV center). The efficiency obtained for parallelepiped detectors, 40mm CZT equivalent to 10mm LSO, could be greatly improved, especially pertaining to the homogeneity across the field of view, if a new trapezoidal geometry for the CZT detector could be implemented. With the objective to confirm the simulation results, a multi-channel experimental bench has been set up. It consists of two detectors put one behind the other to obtain a total depth of 40mm. The 16 anodes and 10 cathodes are connected to 26 identical preamplifiers. The generated signals are fed into customized constant fraction discriminators put on 8 electronic boards, each controlled by an FPGA. The data are processed through a Labview program. CZT-BaF2 coincidence times of 2.1ns FWHM on anodes and 1.6ns FWHM on cathodes have been obtained. After energy calibration and fine tune of threshold, the spatial distribution appears homogeneous along cathode directions and follow the law of absorption along anode directions. Work is in progress now to confirm experimentally the good spatial resolution homogeneity due to the DOI and detection efficiency obtained by simulation. Simulations at the scale of a whole small animal PET system coupled to an experimental validation of these results are under way. This new 3D CZT detector geometry may open up new vistas for innovative system architectures, particularly regarding the global sensitivity improvement.