Development of brain PET using GAPD arrays
ABSTRACT In recent times, there has been great interest in the use of Geiger-mode avalanche photodiodes (GAPDs) as scintillator readout in positron emission tomography (PET) detectors because of their advantages, such as high gain, compact size, low power consumption, and magnetic field insensitivity. The purpose of this study was to develop a novel PET system based on GAPD arrays for brain imaging.
The PET consisted of 72 detector modules arranged in a ring of 330 mm diameter. Each PET module was composed of a 4 × 4 matrix of 3 × 3 × 20 mm(3) cerium-doped lutetium yttrium orthosilicate (LYSO) crystals coupled with a 4 × 4 array three-side tileable GAPD. The signals from each PET module were fed into preamplifiers using a 3 m long flat cable and then sent to a position decoder circuit (PDC), which output a digital address and an analog pulse of the interacted channel among 64 preamplifier signals transmitted from four PET detector modules. The PDC outputs were fed into field programmable gate array (FPGA)-embedded data acquisition (DAQ) boards. The analog signal was then digitized, and arrival time and energy of the signal were calculated and stored.
The energy and coincidence timing resolutions measured for 511 keV gamma rays were 18.4 ± 3.1% and 2.6 ns, respectively. The transaxial spatial resolution and sensitivity in the center of field of view (FOV) were 3.1 mm and 0.32% cps/Bq, respectively. The rods down to a diameter of 2.5 mm were resolved in a hot-rod phantom image, and activity distribution patterns between the white and gray matters in the Hoffman brain phantom were well imaged.
Experimental results indicate that a PET system can be developed using GAPD arrays and the GAPD-based PET system can provide high-quality PET imaging.
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ABSTRACT: Purpose: The aim of this study was to develop a prototype magnetic resonance (MR)-compatible positron emission tomography (PET) that can be inserted into a MR imager and that allows simultaneous PET and MR imaging of the human brain. This paper reports the initial results of the authors' prototype brain PET system operating within a 3-T magnetic resonance imaging (MRI) system using newly developed Geiger-mode avalanche photodiode (GAPD)-based PET detectors, long flexible flat cables, position decoder circuit with high multiplexing ratio, and digital signal processing with field programmable gate array-based analog to digital converter boards.Methods: A brain PET with 72 detector modules arranged in a ring was constructed and mounted in a 3-T MRI. Each PET module was composed of cerium-doped lutetium yttrium orthosilicate (LYSO) crystals coupled to a tileable GAPD. The GAPD output charge signals were transferred to preamplifiers using 3 m long flat cables. The LYSO and GAPD were located inside the MR bore and all electronics were positioned outside the MR bore. The PET detector performance was investigated both outside and inside the MRI, and MR image quality was evaluated with and without the PET system.Results: The performance of the PET detector when operated inside the MRI during MR image acquisition showed no significant change in energy resolution and count rates, except for a slight degradation in timing resolution with an increase from 4.2 to 4.6 ns. Simultaneous PET∕MR images of a hot-rod and Hoffman brain phantom were acquired in a 3-T MRI. Rods down to a diameter of 3.5 mm were resolved in the hot-rod PET image. The activity distribution patterns between the white and gray matter in the Hoffman brain phantom were well imaged. The hot-rod and Hoffman brain phantoms on the simultaneously acquired MR images obtained with standard sequences were observed without any noticeable artifacts, although MR image quality requires some improvement.Conclusions: These results demonstrate that the simultaneous acquisition of PET and MR images is feasible using the MR insertable PET developed in this study.Medical Physics 04/2013; 40(4):042503. DOI:10.1118/1.4793754 · 3.01 Impact Factor
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ABSTRACT: Adapting acquisition electronics to new detector designs has often led to complications and compromises. As we developed depth-of-interaction detector designs based on both discrete crystal arrays (dMiCE) and monolithic crystals (cMiCE) concepts, we found that our previous electronics design was inadequate to the task and launched a design effort we have termed our Phase II electronics. The system is based on a basic card design (the Phase II board) that has a large field programmable gate array (FPGA) with sufficient static RAM to support a variety of pulse processing algorithms our group has developed–including timing estimation, pulse integration with pileup correction, and statistical estimation of the event location in the detector. Here we report on the initial development and testing of the Phase II digital board as a basic building block for data acquisition systems.IEEE Transactions on Nuclear Science 02/2014; 61(1):79-87. DOI:10.1109/TNS.2013.2295037 · 1.46 Impact Factor
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ABSTRACT: Channel reduction techniques are useful for reducing the number of channels being digitized and for constructing cost effective DAQ systems. The purpose of this study was to develop a channel reduction circuit which could be used to identify the interacted channel with a coincidence event from the 256 signals transferred from PET detectors. The channel reduction circuit would then output a channel address and analog pulse corresponding to the valid channel. The circuit, called a “position decoder circuit (PDC)”, consisted of a 256 channel gain adjust circuit, eight 32:1 PDCs, and one 8:1 PDC. Two PDC boards were constructed to evaluate the performance and usefulness of the developed PDC for PET applications. The proof-of-principle PET detector block composed of a 4×4 matrix of detector modules, each of which consisted of a LYSO scintillator coupled to a 4×4 array GAPD, was also constructed. A valid channel was successfully identified by the developed PDC, and the channel address and analog pulse outputs of the interacted channel were accurately measured. The variation of the gains for all detector channels was decreased by about 78% using the gain adjustment circuit implemented in the PDC. Moreover, average energy resolution was improved by approximately 8%. The discrepancy of timing resolutions acquired with and without the PDC was negligibly small. Single/coincidence count rates were 209.3/3.2 cps with the PDC and 232.7/3.8 cps without the PDC. Tomographic image of the hot-rod phantom was successfully acquired using the PDC. Experimental results indicate that the PDC is useful to identify a valid channel among a large number of readout channels of PET detectors. The results also indicate that the PDC is feasible to provide high-quality PET image.Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 03/2014; 741:117–123. DOI:10.1016/j.nima.2013.12.055 · 1.32 Impact Factor