Key Jo Hong

Stanford University, Palo Alto, California, United States

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Publications (35)35.46 Total impact

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    ABSTRACT: Purpose of paper is to confirm the feasibility of acquisition of three dimensional single photon emission computed tomography image from boron neutron capture therapy using Monte Carlo simulation. Prompt gamma ray (478 keV) was used to reconstruct image with ordered subsets expectation maximization method. From analysis of receiver operating characteristic curve, area under curve values of three boron regions were 0.738, 0.623, and 0.817. The differences between length of centers of two boron regions and distance of maximum count points were 0.3 cm, 1.6 cm, and 1.4 cm.
    Applied Physics Letters 01/2014; 104(8). · 3.52 Impact Factor
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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. · 2.91 Impact Factor
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    ABSTRACT: This paper presents the development of filtering methods for positron emission tomography (PET) signals contaminated by radio frequency (RF) pulses for combined PET and clinical 3-T magnetic resonance imaging (MRI). The filtering methods include software, hardware, and hybrid correction methods. In the software correction method, PET signals are assessed, and valid signals are identified based on the characteristics of a typical PET signal using Field-Programmable Gate Array (FPGA)-based programming. The hardware correction method makes use of differential-to-single-ended and low-pass filter circuits for PET analog signals. The hybrid correction method involves the sequential application of both the hardware and software methods. Both valid and contaminated PET signals are measured with an oscilloscope. An evaluation is then made of the performance (energy resolution, photopeak channel, total counts, and coincidence timing resolution) of the PET detector modules with and without various MR sequences (gradient echo, spin echo T1 sequence). For all correction methods, the energy resolution, photopeak position, and coincidence timing resolution with MR sequences are similar (<; 3%) to those without MR sequences. However, the total count of each module depends greatly on the method applied. The hybrid correction method displays an ability to preserve (<; 1%) the total counts of the modules during various MR sequences. The results show that this filtering method, which can reject noise signals and reduce count loss while preserving the valid analog signals of MR sequences, is reliable and useful for the development of simultaneous PET-MRI.
    IEEE Transactions on Nuclear Science 01/2013; 60(5):3205-3211. · 1.22 Impact Factor
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    ABSTRACT: A multi-element silicon photomultiplier (SiPM) based time-of-flight (ToF) detector module for positron emission tomography (PET) has been developed. The detector module is based on a 4 × 4 array of LYSO-SiPM elements (Hamamatsu MPPC S10931-050P), with individual bias supply for each element. Each element is read out by a wideband, low-noise RF amplifier to maximize timing performance. All 16 outputs are digitized with a high-speed CAEN V1742 digitizer module (32 + 2 channels, 5 GS/s sampling, 12-bit amplitude resolution, 500 MHz input bandwidth) to acquire raw pulse waveforms for offline timing and energy extraction. As the digitizer has no internal trigger for individual channels, a trigger board has been developed which produces a fast pulse that triggers the digitizer whenever any pixel of the detector detects a signal in coincidence with a reference detector. To assess the performance of the prototype module, a 4 × 4 LYSO scintillator array ( 3×3×5 mm3 elements) was coupled to the SiPM photodetectors and energy/timing resolution measurements were performed using a Ge-68 source. At 1.4 V overvoltage, the energy resolution, not corrected for saturation effects of the SiPM, varied from a minimum of 10.1% to a maximum of 13.3% with an average energy resolution of 11.4 ± 0.8% across the 16 channels. With a reference detector (single 3×3×5 mm3 LYSO crystal coupled to a Hamamatsu MPPC S10362-33), the average coincidence resolving time (CRT) across the detector module was 206 ± 7 ps FWHM at 2.4 V overvoltage-the best reported for a PET block (array) detector based on conventional photodetectors to date.
    IEEE Transactions on Nuclear Science 01/2013; 60(5):3735-3741. · 1.22 Impact Factor
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    ABSTRACT: In this paper, we describe current trends in data path topologies for Positron Emission Tomography (PET) data acquisition (DAQ) systems which is used to capture signals from the detector modules and generate coincidence data for a image reconstruction computer. First, the requirements of DAQ systems in PET, such as event throughput, timing resolution, and energy resolution, are analyzed. Then, design issues related to DAQ designs are discussed including multiplexing schemes, DAQ boards interconnection topologies, and transmission protocols to transfer data to the image reconstruction computer. We also discuss how new trends in PET systems, such as time-of-flight (TOF) PET, depth-of-interaction (DOI) information, and PET/MRI, can affect the design of PET DAQ systems.
    IEEE Transactions on Nuclear Science 01/2013; 60(5):3746-3757. · 1.22 Impact Factor
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    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.
    Medical Physics 03/2012; 39(3):1227-33. · 2.91 Impact Factor
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    ABSTRACT: Currently, for most photomultiplier tube (PMT)-based PET systems, constant fraction discriminators (CFD) and time to digital converters (TDC) have been employed to detect gamma ray signal arrival time, whereas anger logic circuits and peak detection analog-to-digital converters (ADCs) have been implemented to acquire position and energy information of detected events. As compared to PMT the Geiger-mode avalanche photodiodes (GAPDs) have a variety of advantages, such as compactness, low bias voltage requirement and MRI compatibility. Furthermore, the individual read-out method using a GAPD array coupled 1:1 with an array scintillator can provide better image uniformity than can be achieved using PMT and anger logic circuits. Recently, a brain PET using 72 GAPD arrays (4×4 array, pixel size: 3mm×3mm) coupled 1:1 with LYSO scintillators (4×4 array, pixel size: 3mm×3mm×20mm) has been developed for simultaneous PET/MRI imaging in our laboratory. Eighteen 64:1 position decoder circuits (PDCs) were used to reduce GAPD channel number and three off-the-shelf free-running ADC and field programmable gate array (FPGA) combined data acquisition (DAQ) cards were used for data acquisition and processing. In this study, a free-running ADC- and FPGA-based signal processing method was developed for the detection of gamma ray signal arrival time, energy and position information all together for each GAPD channel. For the method developed herein, three DAQ cards continuously acquired 18 channels of pre-amplified analog gamma ray signals and 108-bit digital addresses from 18 PDCs. In the FPGA, the digitized gamma ray pulses and digital addresses were processed to generate data packages containing pulse arrival time, baseline value, energy value and GAPD channel ID. Finally, these data packages were saved to a 128Mbyte on-board synchronous dynamic random access memory (SDRAM) and then transferred to a host computer for coincidence sorting and image reconstruction. In order to evaluate the functionality of the developed signal processing method, energy and timing resolutions for brain PET were measured via the placement of a 6μCi 22Na point source at the center of the PET scanner. Furthermore the PET image of the hot rod phantom (rod diameter: from 2.5mm to 6.5mm) with activity of 1mCi was simulated, and then image acquisition experiment was performed using the brain PET. Measured average energy resolution for 1152 GAPD channels and system timing resolution were 19.5% (FWHM%) and 2.7ns (FWHM), respectively. With regard to the acquisition of the hot rod phantom image, rods could be resolved down to a diameter of 2.5mm, which was similar to simulated results. The experimental results demonstrated that the signal processing method developed herein was successfully implemented for brain PET. This reduced the complexity, cost and developing duration for PET system relative to normal PET electronics, and it will obviously be useful for the development of high-performance investigational PET systems.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 02/2012; · 1.14 Impact Factor
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    ABSTRACT: Coincidence detection and the high event rates make data acquisition (DAQ) a challenge for Positron Emission Tomograpy (PET). The data path structures inside a DAQ system in PET have been changing with technological advancements in both communication devices and semiconductor based photo-detectors. Time-of-flight (TOF) detection capability or magnetic resonance imaging (MRI) compatibility place new requirements on the detection signal chain. In this paper, we describe the current trends in the data path structures for PET DAQ systems, which handle the PET signal processing chain from detector modules to the data acquisition PC for real-time data extraction. DAQ systems are quantitatively described by the event throughput, timing resolution, and energy resolution. Different readout multiplexing schemes, DAQ board interconnection schemes, and transmission protocols related data acquisition PC are covered. We will also discuss how new PET scanner technologies such as TOF and PET/MRI have introduced new requirements for PET DAQ systems. Furthermore, we explore how the advancements in communication devices, such as high-speed serial buses and optical transceivers, can be utilized for interconnections within the DAQ system.
    Real Time Conference (RT), 2012 18th IEEE-NPSS; 01/2012
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    ABSTRACT: We developed a data acquisition (DAQ) system for positron emission tomography (PET) that can efficiently process detector module signals with compressed sensing multiplexing schemes. This multiplexing scheme has a multiplexing ratio of 8:1 and the capability to resolve multi-hit events or light sharing events even at very high singles rates. To process the compressed signals, a conventional DAQ system structure had to be modified. It needs to process 16 ADC channels simultaneously and process large coincidence packets efficiently. We design simultaneous 32 channel ADC sampling scheme to process 16 channel simultaneously at the FPGA. The "asymmetric coincidence processing" was used for coincidence identification which reduced the required network speed. The measured maximum singles events rate was 3.6 Mevent/s per compressed sensing processor which will be 74.7 Mevent/s for all the system. Identified coincidences could be downloaded to a data acquisition PC at 1.2 Mevent/s at maximum. Other free-running analog-to-digital converter (A DC) based systems can also benefit from the proposed asymmetric processing scheme to increase system throughput. Index TermsPositron emission tomography (PET), data acquisition system (DAQ), compressed sensing, coincidence event processing, asymmetric coincidence processing.
    Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2012 IEEE; 01/2012
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    ABSTRACT: We have developed a FPGA-based time-to-digital converter (TDC) that can be used for a TOF-PET block detector based on silicon photomultiplier (SiPM) photodetectors. The tapped delay line (TDL) method implemented with a dedicated carry chain structure was used to measure short time intervals. The proposed TDC, implemented in a Spartan-6 FPGA, consists of a fine time measurement block, a coarse counter, a ring oscillator and a multiplexer. The ring oscillator generates a delay chain related frequency which is used to compensate process, voltage and temperature (PVT) effects in real-time without causing dead-time in the TDC. The multiplexer allows multiple channels to share the same delay chain which effectively reduces the amount of FPGA resources. As the TDC is implemented in an shared FPGA device, which already exists in a data acquisition system (DAQ), TOF capability can be implemented easily without requiring more resources. The performance of our proposed TDC was first measured with two input pulses which were generated from a pulse generator but with different delay lengths. Timing resolution of a TDC channel is 41.6 ± 1.1 ps FWHM (17.7 ± 0.5 ps RMS). The proposed TDC was also used to measure the timing resolution of a pair of TOF-PET detector with a Hamamatsu MPPC coupled to a 3 mm × 3 mm face of a 2 mm × 2 mm × 3 mm LYSO crystal. The measured coincidence time resolution was 197 ± 4 ps FWHM which agreed with the value measured by a high speed oscilloscope (195 ± 7 ps FWHM). These results verify the feasibility of our TDC for TOF-PET applications.
    Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2012 IEEE; 01/2012
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    ABSTRACT: Positron emission tomography (PET) employing Geiger-mode avalanche photodiodes (GAPDs) and charge signal transmission approach was developed for small animal imaging. Animal PET contained 16 LYSO and GAPD detector modules that were arranged in a 70 mm diameter ring with an axial field of view of 13 mm. The GAPDs charge output signals were transmitted to a preamplifier located remotely using 300 cm flexible flat cables. The position decoder circuits (PDCs) were used to multiplex the PET signals from 256 to 4 channels. The outputs of the PDCs were digitized and further-processed in the data acquisition unit. The cross-compatibilities of the PET detectors and MRI were assessed outside and inside the MRI. Experimental studies of the developed full ring PET were performed to examine the spatial resolution and sensitivity. Phantom and mouse images were acquired to examine the imaging performance. The mean energy and time resolution of the PET detector were 17.6% and 1.5 ns, respectively. No obvious degradation on PET and MRI was observed during simultaneous PET-MRI data acquisition. The measured spatial resolution and sensitivity at the CFOV were 2.8 mm and 0.7%, respectively. In addition, a 3 mm diameter line source was clearly resolved in the hot-sphere phantom images. The reconstructed transaxial PET images of the mouse brain and tumor displaying the glucose metabolism patterns were imaged well. These results demonstrate GAPD and the charge signal transmission approach can allow the development of high performance small animal PET with improved MR compatibility.
    Journal of Instrumentation 08/2011; 6(08):P08012. · 1.66 Impact Factor
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    ABSTRACT: The use of a dual-ended readout PET detector module based on Geiger-mode avalanche photodiodes (GAPDs) with large-area microcells was proposed to obtain high photon detection efficiency (PDE) and overcome energy non-linearity problems. A simulation study was performed and experimental measurement were taken for the single- and dual-ended PET detector modules consisting of the two types of GAPDs with 50 × 50 μm2 and 100 × 100 μm2 microcells. A Monte Carlo simulation was conducted to predict the number of incident photons impinging on the GAPD entrance surface to estimate the light collection efficiency (LCE) and energy linearity performance. A depth of interaction (DOI) ratio histogram was also obtained. An experimental study was performed to acquire the spectra of different energy γ-rays, and the energy linearity was evaluated by analyzing the photo-peak channels. The simulation results showed that the LCE and energy linearity of the dual-ended PET detector modules were considerably improved compared to the single-ended one, with 100 × 100 μm2 microcell GAPDs. We also estimated that the proposed method can provide accurate (3–4 mm) and uniform DOI resolution. In the experimental measurement, the 511 keV photo-peak channels of the dual-ended PET detector modules were increased 26% and 71% compared to the single-ended one, with 50 × 50 μm2 and 100 × 100 μm2 microcell GAPDs, respectively. The coefficients of determination (R2) were increased from 0.97 to 0.99 and from 0.86 to 0.93 with 50 × 50 μm2 and 100 × 100 μm2 microcell GAPDs, respectively. The results of this study demonstrate that the dual-ended readout scheme using GAPDs with large-area microcells provides high LCE and DOI information with minimized energy non-linearity. This will enable investigators to configure PET detector modules with high sensitivity and resolution.
    Journal of Instrumentation 07/2011; 6(07):P07003. · 1.66 Impact Factor
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    ABSTRACT: We examined a PET detector consisting of an LYSO array coupled to a 4 × 4 array of large-size Geiger-mode avalanche photodiode (GAPD). The GAPD coupled to 3 mm × 3 mm × 20 mm LYSO pixel crystal has been investigated for possible use as an MR-compatible PET photosensor. Primary characteristics of a PET detector, such as energy resolution and coincidence timing resolution were measured. Gain variation, count uniformity, and count estimation error of 4 × 4 array of LYSO-GAPD were measured to evaluate the performance parameters relevant for PET imaging. The energy resolution and coincidence timing resolution with 511 keV gamma rays were 18.5 ± 0.7% and 1.6 ns, respectively. The gain variation, count uniformity for all 16 channels were 1.3:1 and 1.3:1, respectively. The count estimation error between adjacent channels measured with an LYSO connected to a GAPD pixel was negligible (0.24 ± 0.04%). Long-term stability results show that there was no significant change in the photopeak position, energy resolution and count rate for 20 days. Cable lengths up to 300 cm, used between the GAPD and preamplifier, did not affect photopeak position and energy resolution. The performance of the LYSO-GAPD detector inside the MRI exhibited no significant change compared to that measured outside the MRI. The MR images acquired with and without the operating LYSO-GAPD detector located on top of the RF coil showed no considerable degradation in image quality. These results demonstrate the feasibility of using the LYSO-GAPD detector as PET photosensors, which could be used for MR compatible PET development.
    Journal of Instrumentation 05/2011; 6(05):P05012. · 1.66 Impact Factor
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    ABSTRACT: The authors have previously reported a simulation study on a novel multi-pinhole (MP) collimator that is able to provide improved angular sampling and an enlarged imaging field of view (FOV) when compared to a low-energy high-resolution parallel-hole (LEHR) collimator using a detector of equivalent size. The aim of this study was to develop a miniature single photon emission computerized tomography (SPECT) to verify the performance of the proposed MP collimator with lead vertical septa. A detector with a 70mm×70mm active area that consisted of a 6mm-thick NaI(Tl) crystal coupled to a 127mm-diameter position-sensitive photomultiplier tube (PSPMT) was used. A 7×7 pinhole collimator with a 2mm-diameter pinhole and a focal length of 40mm was fabricated to evaluate the performance as compared to a typical LEHR collimator. Additionally, a detector having a 50mm×50mm active area with 5×5 pinhole and LEHR collimators was investigated to evaluate the enlarged imaging FOV. Planar spatial resolution, sensitivity, and resolution for hot- and cold-rod phantom images were acquired. Images were reconstructed using a dedicated maximum likelihood expectation maximization (MLEM) algorithm with an unmatched projector/backprojector pair. The spatial resolution and sensitivity obtained with both collimators were 4.7mm FWHM and 0.25cps/μCi at a distance of 60mm, respectively. Although the detector size was smaller than the phantom, the MP collimator allowed for imaging of the entire phantom while the image obtained with LEHR collimator suffered from a truncation artifact. The reconstructed images, using 60 and 30 projections with both 7×7 pinhole and LEHR collimators, yielded an image of similar quality to that, which was constructed using 120 projections. However, the images reconstructed with 10 projections using a 7×7 pinhole collimator showed better quality than those that used an LEHR collimator. The reconstructed images that used the MP collimator provided high-quality images with an enlarged imaging FOV, even when insufficient angular sampling data were used, which would be of use in the development of a stationary SPECT.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2011; 633(1):61-65. · 1.14 Impact Factor
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    ABSTRACT: Light sharing PET detector configuration coupled with thick light guide and Geiger-mode avalanche photodiode (GAPD) with large-area microcells was proposed to overcome the energy non-linearity problem and to obtain high light collection efficiency (LCE). Theoretical evaluations were performed for 90 types of PET detector modules. A Monte Carlo simulation was conducted for the three types of LSO block, 4×4 array of 3×3×20 mm<sup>3</sup>, 6×6 array of 2×2×20 mm<sup>3</sup>, and 12×12 array of 1×1×20 mm<sup>3</sup> discrete crystals, to investigate the scintillation light distribution after conversion of the γ-rays in LSO. The incident photons were read out by three types of 4×4 array photo-sensors, which were PSPMT of 25% quantum efficiency (QE), GAPD1 with 50×50 μm<sup>2</sup> microcells of 30% photon detection efficiency (PDE) and GAPD2 with 100×100 μm<sup>2</sup> of 45% PDE. The number of counted photons in each photo-sensor was analytically calculated. The LCE, linearity and flood histogram were examined for each PET detector module as a function of light guide thickness ranging from 1 to 10 mm. The performance of PET detector modules based on GAPDs was significantly improved by using the thick light guide. The LCE was increased from 24 to 30% and from 14 to 41%, and the linearity was also improved from 0.96 to 0.99, from 0.78 to 0.99, for GAPD1 and GAPD2, respectively. In the contrary, the performance was not changed for PSPMT based detector. The flood histogram of 12×12 array PET detector modules using 3 mm light guide coupled with GAPDs was obtained by simulation, and all crystals of 1×1×20 mm<sup>3</sup> size was clearly identified. PET detector module coupled with thick light guide and GAPD array with large-area microcells was proposed to obtain high QE and high spatial resolution, and its feasibility was verified. It- - demonstrates GAPDs could be a competitive and cost-effective photo-sensor respect to the high QE (~40%) PMT.
    Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE; 12/2010
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    ABSTRACT: A dual-ended readout PET detector module based on Geiger-mode avalanche photodiode (GAPD) with large-area microcells was proposed to obtain high photon detection efficiency (PDE) and to overcome the energy non-linearity problem. Theoretical analysis and experimental measurement were performed for the single- and dual-ended PET detector modules which were consisted of the two types of GAPDs with 50×50 μm<sup>2</sup> and 100×100 μm<sup>2</sup> microcell sizes. A Monte Carlo simulation was conducted to predict the number of incident photons impinging on the GAPD entrance surface to estimate the light collection efficiency (LCE) and linearity performance. Also, the depth of interaction (DOI) ratio histogram was obtained. Experimental study was performed to acquire the energy spectra of different γ-rays, and the linearity was evaluated by analyzing the photo-peak channels. The simulation results showed the LCE of dual-ended PET detector modules were improved 9% and 55% comparing to the single-ended one, with 50×50 μm<sup>2</sup> and 100×100 μm<sup>2</sup> microcells GAPDs, respectively. Also, it was estimated that the proposed method can provide excellent (3-4 mm) and uniform DOI resolution. In the experimental measurement, the 511 keV photo-peak channels of dual-ended PET detector modules was increased 26% and 71% comparing to the single-ended one, with 50×50 μm<sup>2</sup> and 100×100 μm<sup>2</sup> microcells GAPDs, respectively. The coefficient of determination (R<sup>2</sup>) was improved from 0.86 to 0.93 with 100×100 μm<sup>2</sup> microcells GAPD. The similar improvement in photo-peak channel and linearity was observed in the simulation results. It demonstrated that the dual-ended PET detector configuration could considerably improve the non-linearity properties of GAPD without modification of microcell size and, hence, such configuration could - - provide high LCE, as well as DOI capabilities, for high PET detector performance.
    Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE; 12/2010
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    ABSTRACT: We have previously reported that a brain PET using GAPD arrays was successfully developed. The brain PET consisted of 72 4 × 4 GAPD arrays combined with LYSO crystals (single pixel size: 3 mm × 3 mm). Each 4 GAPD arrays' output signals were sent to a 64:1 position decoder circuit (PDC) which detects the fastest gamma signal of 64 input channels. To further improve the PET system performance, several modifications were performed on the DAQ system: PET data from 3 DAQ cards were transferred and saved on one SDRAM module by rapid channel communication; parallel processing and multiplexing based FPGA algorithm was developed to detect true PET signals by real time; a more user-friendly GUI DAQ control program was developed to control 3 DAQ cards simultaneously; an accurate and fast coincidence sorting method containing 3 discrimination approaches (time, energy and line of response discriminations) was developed to improve image quality. To evaluate the improved DAQ system, several experiments were performed such as sensitivity measurement using a 25 μά Na-22 point source, spatial resolution measurement using ten F-18 line sources with different source-to-center distances (-8 cm, -6 cm, -4 cm, -2 cm, 0, 2 cm, 4 cm, 6 cm, 8 cm and 10 cm), PET images acquisition of hot rod phantom and Hoffman brain phantom. Experimental results showed that PET sensitivity of 2594 cps/ MBq at 30% energy window (350-650 kev) was achieved. Spatial resolution from 2.9 mm (center) to 5 mm (25 cm off-center) was acquired for ten different source-to-center distances. PET images of hot rod phantom and Hoffman brain phantom were successfully acquired with improved image quality. The DAQ system developed in this study allows to acquiring high quality PET images using GAPD arrays.
    Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE; 12/2010
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    ABSTRACT: A new positron emission tomography (PET) detector signal processing method, the charge signal transmission approach, is proposed for the development of a hybrid PET-magnetic resonance imaging (MRI). A number of experiments were performed to demonstrate that the Geiger-mode avalanche photodiode (GAPD) charge output could be transmitted to a preamplifier using a long cable without degrading the PET signal performance. A PET module consisted of LYSO and a GAPD with a 4 x 4 array. The GAPD output was transmitted to the preamplifier through flexible flat cables. The effect of the cable length on the PET performance was examined using seven different lengths ranging from 10 to 300 cm outside and inside the 7 T animal MRI. Four parameters (rise time, fall time, amplitude, and area of the preamplifier output) were measured as a function of the cable length using a 10 GS/s oscilloscope and three parameters (photopeak position, energy resolution, and time resolution) were measured using a 100 MS/s DAQ unit. The effect of the cable length on the MR phantom images was investigated. In addition, the effect of the PET module configuration on its temperature stability was assessed by acquiring the energy and time spectra. There were no significant changes in the PET module performance as a function of the cable length, both outside and inside MRI. The performance changes in energy information, such as the amplitude, area, photopeak position, and energy resolution, were <3% with cable lengths ranging from 10 to 300 cm and the change in the time resolution was <6%. There were no obvious artifacts or changes in the line profile in the MR phantom images. Moreover, no manifest changes in the photopeak position and coincidence counting rate were observed in the PET modules employing the charge signal transmission approach, whereas considerable degradation of the PET module performance was observed in the voltage signal transmission approach. This study demonstrated that it is feasible to design a hybrid PET-MRI using the charge signal transmission approach, which is expected to have more advantages than other approaches.
    Medical Physics 11/2010; 37(11):5655-64. · 2.91 Impact Factor
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    ABSTRACT: Use of channel reduction techniques that reduce the number of signals transmitted to a data acquisition (DAQ) module can lead to more efficient use of the DAQ module for PET with numerous readout channels. The purpose of this study was to develop a position decoder circuit (PDC) with a capacity to output the digital address and analog pulse of one interacted channel from numerous PET outputs. A PDC capable of reducing the number of readout channels by a factor of 32 was designed and fabricated. PET detector modules consisting of an LYSO scintillator, a 4×4 array Geiger-mode avalanche photodiode (GAPD), and a 16-channel preamplifier were also constructed to evaluate the performance of the PDC developed for this study. The output signal from the PET detector module was transmitted to the DAQ module after a 45ns delay by the PDC. Using the gain correction circuit implemented in the PDC, gain uniformity for all channels of the PET detector module was improved by 80%. Energy resolution in the PET detector was 20.4% with the PDC and 20.8% without the PDC. Timing resolution was 2.2ns with the PDC and 1.5ns without the PDC. A hot-rod phantom image was successfully acquired using proof-of-principle PET with the PDC developed for this study. Experimental results indicate that the PDC developed for this study is not only useful for the reduction of the readout channel number from the PET detector module consisting of GAPD arrays, but also for PET signal processing and PET imaging.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 09/2010; 621(1):310-315. · 1.14 Impact Factor
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    ABSTRACT: The aim of this study is to develop a MR compatible PET that is insertable to MRI and allows simultaneous PET and MR imaging of human brain. The brain PET having 72 detector modules arranged in a ring of 330 mm diameter was constructed and mounted in a 3-T MRI. Each PET module composed of 4 × 4 matrix of 3 mm × 3 mm × 20 mm LYSO crystals coupled to a tileable 4 × 4 array Geiger-mode avalanche photodiode (GAPD) and designed to locate between RF and gradient coils. GAPD output charge signals were transferred to preamplifiers using flat cable of 3 m long, and then sent to position decoder circuit (PDC) identifying digital address and generating an analog pulse of the one interacted channel from preamplifier signals. The PDC outputs were fed into FPGA-embedded DAQ boards. The analog signal was digitized, and arrival time and energy of the signal were calculated and stored. LYSO and GAPD were located inside MR bore and all electronics including preamplifiers were positioned outside MR bore to minimize signal interference between PET and MR. Simultaneous PET/MR images of a hot-rod and Hoffman brain phantom were acquired in a 3-T MRI using the MR compatible PET system. The rods down to a diameter of 3.5 mm were resolved in the hot-rod PET image. Activity distribution patterns between white and gray matter in Hoffman brain phantom were well imaged. No degradation of image quality of the hot-rod and Hoffman brain phantoms on the simultaneously acquired MR images obtained with standard sequences was observed. These results demonstrate that simultaneous acquisition of PET and MR images is feasible using the MR insertable PET developed in this study.
    IEEE Nuclear Science Symposium conference record. Nuclear Science Symposium 01/2010;

Publication Stats

92 Citations
35.46 Total Impact Points

Institutions

  • 2012–2014
    • Stanford University
      • Department of Radiology
      Palo Alto, California, United States
  • 2010–2013
    • Sogang University
      • Department of Electronic Engineering
      Seoul, Seoul, South Korea
  • 2004–2009
    • Sungkyunkwan University
      • • School of Medicine
      • • Department of Nuclear Medicine
      Seoul, Seoul, South Korea