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In this study, the effect of Cl activation treatment on performance indicators of CdS/CdTe solar cells was investigated. We improved the performance of CdTe solar cells by applying a novel double treatment method that combines the CdCl2 dipping treatment and Freon (difluoro chloromethane) treatment methods that were previously studied. Conventional CdCl2 methanol dipping treatment (CdCl2 dipping treatment), Freon gas treatment that includes chlorine (Freon treatment), and CdCl2 dipping treatment + Freon treatment (double treatment) were performed, and the efficiencies, open circuit voltage (V OC ), and short circuit current (J SC ) for all three processes were observed. Although the efficiencies of the CdCl2 dipping treatment and Freon treatment were similar, there was a trade-off between the V OC and J SC in both processes. The double treatment sample shows an efficiency of 14.3%, which was higher than that of a single-treated sample. To investigate the characteristic change of each part of the solar cell, an equivalent circuit model in which the device was divided into a main junction and a back contact was used. In addition to electrical measurements, secondary ion mass spectroscopy (SIMS) and time of flight (TOF) analysis were performed. Through TOF measurement, drift mobility values for three treatment samples were calculated to be 1.1 cm 2/Vs, 1.8 cm 2/Vs, and 1.9 cm 2/Vs, respectively. With TOF measurement, it was proved that the double treatment had a significant influence on the efficiency of the sample.

Surface modification of ceramic Ce-doped Gd3Al2Ga3O12 (Ce:GAGG) was performed by exposing small samples to anhydrous phosphoric acid (H3PO4) under different conditions (temperature and duration) to investigate the effects of chemical polishing treatment. When coupled to a photomultiplier tube (PMT) and used as a radiation detector, chemical treatment for 3 min at 190 °C improved the light (signal) output by 24.8% and energy resolution by 2.5% (percentage point), respectively. This can be attributed to a reduction in surface roughness that enhanced optical properties. Thus, chemical polishing could be a low-cost alternative to mechanical polishing especially for small or complex shaped ceramic scintillators.

In CdS/CdTe solar cells, Cu is added during the formation of the metallic electrode to enhance the contact properties and achieve an appropriate hole concentration in the cadmium telluride (CdTe) layer. In this study, we added Cu to CdS/CdTe solar cells using two different electrode materials: metallic Cu and Cu2Te layers. They were deposited on the CdTe surface in the CdS/CdTe solar cells, and subsequent annealing was carried out to form a single-phase copper telluride compound. The devices made by these two materials were comparatively investigated in terms of their contact properties such as barrier height, hole density, and contact resistance. Most of the data indicate that the Cu2Te-deposited cell is superior to the Cu-deposited cell. Furthermore, we obtained an optimum annealing condition for the Cu2Te process, at which the cell performance is maximized. These results demonstrate the excellence of the Cu2Te material and provide practical information about the processing technique of this material.

Metal nanoparticles (NPs) are incorporated in solar cells during the formation of front or back contacts to improve light absorption via the scattering of excitation light at their surface plasmon resonance (SPR) or localized SPR (LSPR). Here, we demonstrate LSPR-promoted improvement in the efficiency of CdS/CdTe solar cells fabricated by physical vapor deposition by incorporating different quantities of chemically synthesized 200-nm Au NPs in the CdTe layer. The J-V characteristics, external quantum efficiencies, absorption spectra, and cell efficiencies of these devices are compared. This study can guide future research on enhancing the CdS/CdTe solar cell performance using the plasmon effect.

Recently, we have developed the second prototype Silicon photomultiplier (SiPM) based positron emission tomography (PET) scanner for human brain imaging. The PET system was comprised of detector block which consisted of 4×4 SiPMs and 4×4 Lutetium Yttrium Orthosilicate arrays, charge signal transmission method, high density position decoder circuit and FPGA-embedded ADC boards. The purpose of this study was to evaluate the performance of the newly developed neuro-PET system. The energy resolution, timing resolution, spatial resolution, sensitivity, stability of the photo-peak position and count rate performance were measured. Tomographic image of 3D Hoffman brain phantom was also acquired to evaluate imaging capability of the neuro-PET. The average energy and timing resolutions measured for 511 keV gamma rays were 17±0.1% and 3±0.3 ns, respectively. Spatial resolution and sensitivity at the center of field of view (FOV) were 3.1 mm and 0.8%, respectively. The average scatter fraction was 0.4 with an energy window of 350–650 keV. The maximum true count rate and maximum NECR were measured as 43.3 kcps and 6.5 kcps at an activity concentration of 16.7 kBq/ml and 5.5 kBq/ml, respectively. Long-term stability results show that there was no significant change in the photo-peak position, energy resolution and count rate for 60 days. Phantom imaging studies were performed and they demonstrated the feasibility for high quality brain imaging. The performance tests and imaging results indicate that the newly developed PET is useful for brain imaging studies, if the axial FOV is extended to improve the system sensitivity.

We experimentally investigated the transport properties near metal electrodes installed on a conducting channel in a LaAlO3/SrTiO3 interface. The local region around the Ti and Al electrodes has a higher electrical conductance than that of other regions, where the upper limits of the temperature and magnetic field can be well defined. Beyond these limits, the conductance abruptly decreases, as in the case of a superconductor. The samples with the Ti- or Al-electrode have an upper-limit temperature of approximately 4 K, which is 10 times higher than the conventional superconducting critical temperature of LaAlO3/SrTiO3 interfaces and delta-doped SrTiO3. This phenomenon is explained by the mechanism of electron transfer between the metal electrodes and electronic d-orbitals in the LaAlO3/SrTiO3 interface. The transferred electrons trigger a phase transition to a superconductor-like state. Our results contribute to the deep understanding of the superconductivity in the LaAlO3/SrTiO3 interface and will be helpful for the development of high-temperature interface superconductors.

We experimentally investigated the transport properties near metal electrodes installed on a conducting channel in a LaAlO3/SrTiO3 interface. The local region around the Ti and Al electrodes has a higher electrical conductance than that of other regions, where the upper limits of the temperature and magnetic field can be well defined. Beyond these limits, the conductance abruptly decreases, as in the case of a superconductor. The samples with the Ti- or Al-electrode have an upper-limit temperature of approximately 4 K, which is 10 times higher than the conventional superconducting critical temperature of LaAlO3/SrTiO3 interfaces and delta-doped SrTiO3. This phenomenon is explained by the mechanism of electron transfer between the metal electrodes and electronic d-orbitals in the LaAlO3/SrTiO3 interface. The transferred electrons trigger a phase transition to a superconductor-like state. Our results contribute to the deep understanding of the superconductivity in the LaAlO3/SrTiO3 interface and will be helpful for the development of high-temperature interface superconductors.

Purpose: The purpose of this study was to develop a dual-modality positron emission tomography (PET)/magnetic resonance imaging (MRI) with insertable PET for simultaneous PET and MR imaging of the human brain. Methods: The PET detector block was composed of a 4 × 4 matrix of detector modules, each consisting of a 4 × 4 array LYSO coupled to a 4 × 4 Geiger-mode avalanche photodiode (GAPD) array. The PET insert consisted of 18 detector blocks, circularly mounted on a custom-made plastic base to form a ring with an inner diameter of 390 mm and axial length of 60 mm. The PET gantry was shielded with gold-plated conductive fabric tapes with a thickness of 0.1 mm. The charge signals of PET detector transferred via 4 m long flat cables were fed into the position decoder circuit. The flat cables were shielded with a mesh-type aluminum sheet with a thickness of 0.24 mm. The position decoder circuit and field programmable gate array-embedded DAQ modules were enclosed in an aluminum box with a thickness of 10 mm and located at the rear of the MR bore inside the MRI room. A 3-T human MRI system with a Larmor frequency of 123.7 MHz and inner bore diameter of 60 cm was used as the PET/MRI hybrid system. A custom-made radio frequency (RF) coil with an inner diameter of 25 cm was fabricated. The PET was positioned between gradient and the RF coils. PET performance was measured outside and inside the MRI scanner using echo planar imaging, spin echo, turbo spin echo, and gradient echo sequences. MRI performance was also evaluated with and without the PET insert. The stability of the newly developed PET insert was evaluated and simultaneous PET and MR images of a brain phantom were acquired. Results: No significant degradation of the PET performance caused by MR was observed when the PET was operated using various MR imaging sequences. The signal-to-noise ratio of MR images was slightly degraded due to the PET insert installed inside the MR bore while the homogeneity was maintained. The change of gain of the 256 GAPD/scintillator elements of a detector block was

G protein-coupled receptors (GPCRs) are a large class of transmembrane receptors categorized into five distinct families: rhodopsin, secretin, adhesion, glutamate, and frizzled. They bind and regulate 80% of all hormones and account for 20-50% of the pharmaceuticals currently on the market. Hundreds of GPCRs integrate and coordinate the functions of individual cells, mediating signaling between various organs. GPCRs are crucial players in tumor progression, adipogenesis, and inflammation. Several studies have also confirmed their central roles in embryonic development and stem cell maintenance. Recently, GPCRs have emerged as key players in the regulation of cell survival, proliferation, migration, and self-renewal in pluripotent (PSCs) and cancer stem cells (CSCs). Our study and other reports have revealed that the expression of many GPCRs is modulated during the generation of induced PSCs (iPSCs) or CSCs as well as during CSC sphere formation. These GPCRs may have crucial roles in the regulation of selfrenewal and other biological properties of iPSCs and CSCs. This review addresses the current understanding of the role of GPCRs in stem cell maintenance and somatic reprogramming to PSCs or CSCs. [BMB Reports 2015; 48(2): 68-80]

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.

Purpose 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. Methods 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. Results 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. Conclusions 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.

RECENTLY, there has been great interest in the study of deriving PET event information from digitally sampled event waveforms. We have reported the feasibility of Multi-Voltage Threshold (MVT) based PET DAQ system using field — programmable-gate-array (FPGA) without ADC and TDC. The goal of this study was to extend MVT based multi-channel analog circuit and DAQ with FPGA which could be utilized for the development of a functional PET system.

Realtime near-infrared (NIR) fluorescence imaging system could be exploited for intraoperative imaging guidance. However, the NIR fluorescence imaging technique attains only small penetration depths (a few centimeters) due to the absorption and scattering of light. The purpose of this study was to develop a realtime intraoperative imaging system using annihilation gamma-ray detectors for localization and laser projectors for visualization of surgical region embedded deep in tissue. The proof-of-principle gamma-ray detectors consisted of two front detector blocks and one backside detector block. The front detector block consisted of 8 detector modules arranged in a blank square shape and the backside detector block was composed of 4 × 8 detector modules. Each detector module was composed of a 4 × 4 array LYSO coupled to a 4 × 4 GAPD array. Front and backside detectors were located at opposite sides of each other. Commercial portable LED laser projector with a luminous flux of 500 ANSI lumens was used for the intra-operative system. Two laser projectors were positioned behind each front detector. The design parameters of the gamma-ray imaging system were adjusted and optimized using a Monte Carlo simulation tool, GATE. The performance of the system spatial resolution and count rate were estimated by simulation and by experiment using 450 kBq Na-22 point source. Experimentally measured spatial resolution and count rate were 4.1 mm and 300 counts per second which were similar to those estimated by the simulation. The beam projected by laser projectors was accurately localized the position of radiation source. Experimental results indicate that realtime intraoperative imaging system combining annihilation gamma-ray detectors and laser projectors proposed in this study would be useful to localize and to visualize surgical region embedded deep in tissue.

A MR compatible PET insert has been developed in our group employing SiPM and a charge signal transmission method that transmits the charge signal of SiPM to subsequent electronics through 4 m long cables. The previously developed PET/MRI system, however, had several limitations, such as the instability of PET performance due to temperature variations inside PET gantry and the degradation of SNR in the MR image due to the inserted PET. The purpose of this study was to optimize the design of PET/MRI system to maintain a stable temperature inside the PET gantry and to minimize mutual interference between PET and MRI. The PET insert was composed of 9 PET detector blocks that were arranged in a circle around the subject with 390 mm diameter and 60 mm axial FOV. Each PET detector block was composed of a 4 × 8 array of detector modules consisted of 4 × 4 array of SiPM and 4 × 4 array of LYSO. The PET detectors were cooled using a water chiller system to compensate temperature fluctuations caused by eddy currents. PET analog electronics were enclosed in an aluminum box and located 50 cm apart from the MR bore. The FPGA-embedded DAQ and power supply were installed at outside MR room. PET performance was measured inside and outside MRI using spin echo and gradient echo sequences. MRI performance was evaluated with and without the PET insert. Human brain imaging was also acquired to evaluate the performance of simultaneous PET and MR imaging. No significant degradation of the PET performance caused by MR was observed when the PET was operated under various MR imaging sequences. The homogeneities and SNRs of MR images obtained with and without the PET insert installed inside the MR bore were similar and changed by only 1% and 3%, respectively. High quality simultaneous PET and MR images of human brain were successfully acquired. Experimental results indicate that simultaneous PET and MR imaging is feasible without considerable mutual interference between PET and MRI by employing the PET/MRI proposed in this study.

SIMULTANEOUS functional and anatomical imaging using PET-MR system has been reported to be useful in preclinical research to investigate various in vivo biological processes [1-3]. The purpose of this study was to develop a MR compatible small animal PET insert and to evaluate the performance of the developed PET and the influence of the PET on MRI performance.

We fabricated a magnetic field sensor made of an InAs quantum-well. Various numbers of magnetic particles were located on the sensor and the stray field generated by the magnetic particles was detected using micro-Hall magnetometry at room temperature. A numerical calculation carried out for this device successfully explained the experimental results and a useful equation relating the signal of the device and the number of particles was deduced.

High purity Pb-doped CdZnTe single crystals were grown by using the vertical Bridgman method. Their electrical properties and X-ray spectrum were investigated. The doping concentration of Pb was about 1 × 10 19 cm - 3 . The resistivity of Pb-doped CdZnTe single crystal was 2 × 10 9 Ω cm . The temperature dependence of the resistivity of these crystals was examined between the region of 200 and 300 K. The plot of log ( ρ ) versus 1000 / T was represented by a straight line with a slope of 380 meV. From the PL spectrum, we have confirmed that type conversion from p to n-type conductivity originated from the compensation process of Cd vacancies, which are the most abundant acceptors in CdZnTe. Also, the effects of Pb-doping on the mobility and X-ray spectra were studied by time-of-flight (TOF) and 241Am spectrum measurements.

The purpose of this study was to develop a dual-modality positron emission tomography (PET)/magnetic resonance imaging (MRI) with insertable PET for simultaneous PET and MR imaging of the human brain.The PET detector block was composed of a 4 × 4 matrix of detector modules, each consisting of a 4 × 4 array LYSO coupled to a 4 × 4 Geiger-mode avalanche photodiode (GAPD) array. The PET insert consisted of 18 detector blocks, circularly mounted on a custom-made plastic base to form a ring with an inner diameter of 390 mm and axial length of 60 mm. The PET gantry was shielded with gold-plated conductive fabric tapes with a thickness of 0.1 mm. The charge signals of PET detector transferred via 4 m long flat cables were fed into the position decoder circuit. The flat cables were shielded with a mesh-type aluminum sheet with a thickness of 0.24 mm. The position decoder circuit and field programmable gate array-embedded DAQ modules were enclosed in an aluminum box with a thickness of 10 mm and located at the rear of the MR bore inside the MRI room. A 3-T human MRI system with a Larmor frequency of 123.7 MHz and inner bore diameter of 60 cm was used as the PET/MRI hybrid system. A custom-made radio frequency (RF) coil with an inner diameter of 25 cm was fabricated. The PET was positioned between gradient and the RF coils. PET performance was measured outside and inside the MRI scanner using echo planar imaging, spin echo, turbo spin echo, and gradient echo sequences. MRI performance was also evaluated with and without the PET insert. The stability of the newly developed PET insert was evaluated and simultaneous PET and MR images of a brain phantom were acquired.No significant degradation of the PET performance caused by MR was observed when the PET was operated using various MR imaging sequences. The signal-to-noise ratio of MR images was slightly degraded due to the PET insert installed inside the MR bore while the homogeneity was maintained. The change of gain of the 256 GAPD/scintillator elements of a detector block was3% for 60 min, and simultaneous PET and MR images of a brain phantom were successfully acquired.Experimental results indicate that a compact and lightweight PET insert for hybrid PET/MRI can be developed using GAPD arrays and charge signal transmission method proposed in this study without significant interference.

Although GAPD has been reported to provide good performance as a PET photosensor, it has significant temperature-dependent gain variations causing the drifting of photo-peaks and hence deteriorating the detection sensitivity. Therefore, it is necessary to develop a realtime photo-peak searching method to ensure to apply proper energy window and to sustain uniform sensitivity. This study presented a new realtime photo-peak search method implemented on FPGA. The method used detected gamma-ray energy information to search photo-peak without calculation of direction and step size. The direction was determinated by acquiring a gamma-ray count that has energy within a search range nearby a searching point, and the step size was fixed. The method used two searching points, valley point and peak point, which could be stored in a few registers in FPGA. The performance was evaluated with the simulated energy spectrum and the experimental data acquired with LYSO-MPPC detector. The photo-peak searching error was 3.1±5.5 keV with the simulated energy spectrum with 11% energy resolution, 7.0±7.1 keV with the experimental data. The proposed method successfully found the photo-peak in both the simulation and the experimental study. It is expected that the method could be a powerful realtime searching method to implement on digital circuit for radiation counting system. Since the performance of the searching method depended on searching step size, energy detection range and initial searching point, additional experimental study for the optimization of the parameter will be performed.

We developed MR insertable small animal PET utilizing high resolution event positioning circuit and charge signal transmission approach. A further study will be performed to improve PET image quality by applying correction algorithms and to evaluate the performance of small animal PET mounted inside the MR bore to simultaneously acquire hybrid PET/MR images.

Oxygen partial pressure in a growth process of lead oxide determines chemical and physical properties as well as crystalline structure. In order to supply oxygen, two ring-shape suppliers have been installed in a growth chamber. Films have been deposited using vacuum thermal evaporation from a raw material of yellow lead oxide powder (5N). Growth rate is controlled to be about 400 A/s, and film thickness more than 50 μm has been achieved. After deposition, the film is annealed at various temperatures under an oxygen atmosphere. In this study, an optimum growth condition for a good X-ray detector has been achieved by fine control of oxygen flow-rate and by thermal treatment. An electrical resistivity of 4.5×1012 Ω cm is measured, and is comparable with the best data of PbO.

The purpose of this study was to develop a dual-modality PET/MRI with insertable PET for simultaneous imaging of human brain. The PET insert consisted of 18 detector blocks arranged in a ring of 390 mm diameter with 60 mm axial FOV. Each detector block was composed of 4 × 4 matrix of detector modules, each of which consisted of a 4 × 4 array LYSO coupled to a 4 × 4 GAPD array. The PET gantry was shielded with gold-plated conductive fabric tapes with thickness of 0.1 mm. The charge signals of PET detector transferred via 4 m long flat cables were fed into the position decoder circuit. The flat cables were shielded with a mesh-type aluminum sheet with 0.24 mm thickness. The position decoder circuit and FPGA-embedded DAQ modules were enclosed in an aluminum box with 10 mm thickness and located at the rear of the MR bore inside MRI room. A 3-T human MRI system with a Larmor frequency of 123.7 MHz and bore inner diameter of 60 cm was used for PET/MRI hybrid system. A custom-made radio frequency (RF) coil with inner diameter of 25 cm was fabricated. The PET was positioned between gradient and the RF coils. PET performance was measured outside and inside MRI scanner with spin echo, turbo spin echo and gradient echo sequences. SNR and of MR phantom image were also measured with and without PET insert. The stability of developed PET insert was evaluated and simultaneous PET and MR images of brain phantom were acquired. No significant degradation of the PET performance caused by MR was observed when the PET was operated with various MR imaging sequences. Uniformity and SNR of MR phantom image were degraded about 1% and 7% by the PET insert, respectively. The change of gain of PET detector was

A Geiger-mode avalanche photodiode (GAPD) is actively studied silicon-based photo-detector that is a promising photo-sensor for PET because of various advantages, such as gain, compact size, fast response and magnetic field insensitivity. Previously, we have developed a brain PET employing GAPD-based PET detector block, charge signal transmission method via 4 m long cable, high density position decoder circuit (PDC) and digital signal processing with FPGA-embedded ADC boards. The purpose of this study was to evaluate the performance of the developed brain PET system. The PET consists of 18 detector blocks, each of which comprises 4 × 4 GAPDs and 4 × 4 LYSO arrays. The output signals of PET detector block were amplified by preamplifier circuits and then transferred to the PDC. The PDC was used to identify the one valid channel among 256 channels of PET detector blocks and to output digital address analog pulse corresponding to the valid channel. Three FPGA-embedded DAQ boards were used to digitize analog output signals of the PDCs. The gain uniformity, spatial resolution, sensitivity, stability and count rate performance were measured. Tomographic image of 3D Hoffman brain phantom was also acquired to evaluate imaging capability of the PET. Normalized average photo-peak positions of PET detector block were 1.0 ± 0.14 without the gain correction and 1.0 ± 0.03 with the gain correction. Spatial resolution and sensitivity in the center of field of view were 3.1 mm and 0.8%, respectively. The average scatter fraction was 0.4 with lower energy threshold of 350 keV. The maximum true count rate and maximum NECR were measured 43.3 kcps and 6.5 kcps at an activity concentration of 16.7 kBq/ml and 5.5 kBq/ml, respectively. Activity distribution patterns between white and gray matter in the Hoffman brain phantom were well imaged. These results demonstrate that the developed GAPD based brain PET system is useful for high quality brain PET imaging.

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.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.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.These results demonstrate that the simultaneous acquisition of PET and MR images is feasible using the MR insertable PET developed in this study.

We have reported the usefulness of a channel reduction circuit, called "position decoder circuit (PDC)" generating the digital address and analog pulse of an interacted channel among many PET detector outputs. However, in a previous study, we focused on the design of a POC dedicated to a GAPD-based PET detector with a fast scintillator. The goal of this study was to develop a PDC that could be generally utilized to the various PET detector modules having different physical properties. A PDC, based on two-stage (32:1 and 8:1) channel reduction architecture, was designed. The PDC consisted of: (1) GAPD bias voltage and signal gain adjustment circuits to correct the non-homogeneity and different characteristics of the input signals; (2) a low level discrimination circuit, to reject noise or scatter signals; (3) an analog signal delay and switch circuits to output an analog pulse corresponding to the interacted channel; and (4) a FPGA circuit to identify a valid channel and providing a digital address. Two different types of PET detector modules, LYSO-GAPD (high light output and fast decay time) and BGO-GAPD (low light output and slow decay time), were constructed to evaluate the functionality of the developed PDC. The developed PDC successfully identified the interacted channel. Channel address/analog pulse output signals were generated after 34 nsf 98 ns for LYSO-GAPD and 50 nsf 98 ns for BGO-GAPD compared with input signals, respectively. Measured energy and coincidence timing resolutions for LYSO-GAPD were 18.5% and 2.9 ns, respectively, and for BGO-GAPD, 20% and 7.8 ns, respectively. A hot-rod phantom image of the proof-of-principle PET system consisting of 8 pairs of PET detector modules was successfully acquired. Experimental results indicate that the PDC developed in this study is useful to identify a valid channel among a large number of readout channels of the PET detectors with different physical properties.

There has been great interest in the development of combined PET/MR, a useful tool for both functional and anatomic imaging. We have developed a proof-of-principle MR compatible PET, employing a design concept that uses GAPD arrays as a PET photo-sensor and charge signal transmission method for human brain imaging. The purpose of this study was to design the 2nd version of brain PET with an extended axial field-of-view (FOV) and to evaluate its initial performance. The PET consisted of 18 detector blocks arranged in a ring of 390 mm diameter with 60 mm axial FOV. Each detector block was composed of a 4 × 4 matrix of detector module, each of which consisted of a 4 × 4 array L YSO coupled to a 4-side tileable 4 × 4 GAPD array. The PET gantry was shielded with gold-plated conductive fabric tapes with a thickness of 0.1 mm. PET signals were fed into the position decoder circuit (PDC) generating the digital address and analog pulse of the one interacted channel among the 256 output channels of the detector block, using a 4 m long flat cable. Commercial DAQ modules were used to digitize analog output signals of the PDCs and to store the data in list mode format. The flat cable was shielded with a mesh-type aluminum sheet, which had a thickness of 0.24 mm. All electronics were enclosed in an aluminum box, which had a thickness of 10 mm, located outside the MR bore. Average energy and timing resolutions of the developed PET measured outside the MR room were 18.1±3.2% (n=4,608) and 3.6 ns, respectively. The sensitivity and spatial resolution were 1.2% and 3.1 mm at the center of the field of view, respectively. No significant degradations of PET performance and the uniformity of MR image were observed. Simultaneous PET and MR images of hot-rod phantom and cat brain were successfully acquired. Experimental results indicate that the high performance compact and lightweight PET insert for hybrid PET-MRI can be developed using GAPD arrays and charge signal transmission method.

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.

We report the enhancement of ferroelectric properties in vanadium-doped Bi4Ti3O12 (BIT) thin films deposited by a sol–gel method. Compared to the undoped BIT, V-doped BIT (BTV) showed higher polarizations and a better fatigue resistance as reported in ceramic systems recently [Noguchi et al., Appl. Phys. Lett. 78, 1903 (2001)]. BTV showed a remanent polarization (2Pr) of 15.9 μC/cm2, higher than the value for BIT, 12.5 μC/cm2. The polarization of the BTV thin film capacitor decreased by 19%, while that of the BIT decreased by 23% after the fatigue test with 4×1010 switching cycles.

A PET employing Geiger-mode avalanche photodiode (GAPD) has been designed and developed in our laboratory for simultaneous human brain PET-MR imaging. The purpose of this study is to evaluate the effect of temperature on the performance of the brain PET. The PET gantry including LYSO and GAPD array were placed in a temperature controlled chamber. All electronics including preamplifiers were located outside the chamber to minimize the temperature effect. Energy resolution and photo-peak position of all channels of the brain PET were measured. Count rates of the PET were also measured using 2 different Schemes: fixed energy window and adjusted energy window. All measurement was performed at 10°C ∼ 40°C with 5°C step. Hot-rod phantom was acquired at 10°C, 25°C and 40°C. The energy resolution was degraded from 14% to 30% as the temperature raised. The photo-peak position the coincidence count rates were respectively decreased from 1314 ch to 560 ch, from 2.5 kcps to 0.9 kcps as the temperature raised. When the energy window was adjusted to the photo-peak position, the rates were stable from 10°C to 35°C. In hot-rod phantom images acquired at 10°Cand 25°C, the rods down to a diameter of 3.5 mm were clearly resolved. However the phantom image acquired at 40 °C demonstrated noticeable degradation in image quality. Future study is being conducted to optimize the adjustable window to obtain stable performance of PET system using GAPD as a function of temperature.

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.

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 mm3, 6×6 array of 2×2×20 mm3, and 12×12 array of 1×1×20 mm3 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 μm2 microcells of 30% photon detection efficiency (PDE) and GAPD2 with 100×100 μm2 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 mm3 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.