Block Detector Research Articles

Development of a Whole-Body Dual Ring OpenPET for in-Beam PET

For in-beam positron emission tomography (PET), which is an in situ monitoring method for charged particle therapy, we developed the world’s first open-type PET system “OpenPET.” Following our previous studies for small prototypes, in this paper, we finally developed a whole-body dual ring OpenPET (WBDROP). This scanner has two separated rings. Each ring has two detector rings of 40 detector blocks, each of which has the capability of 4-layer depth-of-interaction identification. The ring diameter is 66 cm, and the adjustable open gap is fixed as 9 cm. We found that the system sensitivity was 4.4%. The average spatial resolution, which was measured through filtered back projection, was about 3.5 mm. For in-beam PET, imaging performance was confirmed through phantom experiments. Phantom study results with 11C beam and 10C beam irradiations of about 3 Gy showed that the beam stopping position in the target could be measured with a precision of better than 2 mm. The developed WBDROP promises high performance for in-beam PET imaging.

A Hardware-Efficient Scalable Spike Sorting Neural Signal Processor Module for Implantable High-Channel-Count Brain Machine Interfaces.

Next-generation brain machine interfaces demand a high-channel-count neural recording system to wirelessly monitor activities of thousands of neurons. A hardware efficient neural signal processor (NSP) is greatly desirable to ease the data bandwidth bottleneck for a fully implantable wireless neural recording system. This paper demonstrates a complete multichannel spike sorting NSP module that incorporates all of the necessary spike detector, feature extractor, and spike classifier blocks. To meet high-channel-count and implantability demands, each block was designed to be highly hardware efficient and scalable while sharing resources efficiently among multiple channels. To process multiple channels in parallel, scalability analysis was performed, and the utilization of each block was optimized according to its input data statistics and the power, area and/or speed of each block. Based on this analysis, a prototype 32-channel spike sorting NSP scalable module was designed and tested on an FPGA using synthesized datasets over a wide range of signal to noise ratios. The design was mapped to 130nm CMOS to achieve 0.75μW power and 0.023mm2 area consumptions per channel based on post synthesis simulation results, which permits scalability of digital processing to 690 channels on a 4×4 mm2 electrode array.

Performance Characteristics of the Whole-Body Discovery IQ PET/CT System.

The aim of this study was to assess the physical performance of a new PET/CT system, the Discovery IQ with 5-ring detector blocks. Methods: Performance was measured using the National Electrical Manufacturers Association NU2-2012 methodology. Image quality was extended by accounting for different acquisition parameters (lesion-to-background ratios [8:1, 4:1, and 2:1] and acquisition times) and reconstruction algorithms (VUE-point HD [VPHD], VPHD with point-spread-function modeling [VPHD-S], and Q.Clear). Tomographic reconstruction was also assessed using a Jaszczak phantom. Additionally, 30 patient lesions were analyzed to account for differences in lesion volume and SUV quantification between reconstruction algorithms. Results: Spatial resolution ranged from 4.2 mm at 1 cm to 8.5 mm at 20 cm. Sensitivity measured at the center and at 10 cm was 22.8 and 20.4 kps/kBq, respectively. The noise-equivalent counting rate peak was 124 kcps at 9.1 kBq/cm3 The scatter fraction was 36.2%. The accuracy of correction for count losses and randoms was 3.9%. In the image quality test, contrast recovery for VPHD, VPHD-S, and Q.Clear ranged from 18%, 18%, and 13%, respectively (hot contrast; 10-mm sphere diameter; ratio, 2:1), to 68%, 67%, and 81%, respectively (cold contrast; 37-mm sphere diameter; ratio, 8:1). Background variability ranged from 3.4%, 3.0%, and 2.1%, respectively (ratio, 2:1), to 5.5%, 4.8%, and 3.7%, respectively (ratio, 8:1). On Q.Clear reconstruction, the decrease in the penalty term (β) increased the contrast recovery coefficients and background variability. With the Jaszczak phantom, image quality increased overall when a reconstruction algorithm modeling the point-spread function was used, and use of Q.Clear increased the signal-to-noise ratio. Lesions analyzed using VPHD-S and Q.Clear had an SUVmean of 6.5 ± 3 and 7 ± 3, respectively (P < 0.01), and an SUVmax of 11 ± 4.8 and 12 ± 4, respectively (P < 0.01). No significant difference in mean lesion volume was found between algorithms. Conclusion: Among the various Discovery bismuth germanium oxide-based PET/CT scanners, the IQ with 5-ring detector blocks has the highest overall performance, with improved sensitivity and counting rate performance. Q.Clear reconstruction improves the PET image quality, with higher recovery coefficients and lower background variability.

PVC extrusion development and production for the NOvA neutrino experiment

We have produced large and highly-reflective open-cell PVC extrusions for the NOvA neutrino oscillation experiment. The extrusions were sealed, instrumented, assembled into self-supporting detector blocks, and filled with liquid scintillator. Each Far Detector block stands 15.7m high, is 15.7m wide and 2.1m thick. More than 22,000 extrusions were produced with high dimensional tolerance and robust mechanical strength. This paper provides an overview of the NOvA Far Detector, describes the preparation of the custom PVC powder, and the making of the extrusions. Quality control was a key element in the production and is described in detail.

Development of a multiplexed readout with high position resolution for positron emission tomography

Detector signals for positron emission tomography (PET) are commonly multiplexed to reduce the number of digital processing channels so that the system can remain cost effective while also maintaining imaging performance. In this work, a multiplexed readout combining Anger position estimation algorithm and position decoder circuit (PDC) was developed to reduce the number of readout channels by a factor of 24, 96-to-4. The data acquisition module consisted of a TDC (50ps resolution), 4-channel ADCs (12bit, 105MHz sampling rate), 2GB SDRAM and USB3.0. The performance of the multiplexed readout was assessed with a high-resolution PET detector block composed of 2×3 detector modules, each consisting of an 8×8 array of 1.52×1.52×6mm3 LYSO, a 4×4 array of 3×3mm2 silicon photomultiplier (SiPM) and 13.4×13.4mm2 light guide with 0.7mm thickness. The acquired flood histogram showed that all 384 crystals could be resolved. The average energy resolution at 511keV was 13.7±1.6% full-width-at-half-maximum (FWHM) and the peak-to-valley ratios of the flood histogram on the horizontal and vertical lines were 18.8±0.8 and 22.8±1.3, respectively. The coincidence resolving time of a pair of detector blocks was 6.2ns FWHM. The reconstructed phantom image showed that rods down to a diameter of 1.6mm could be resolved. The results of this study indicate that the multiplexed readout would be useful in developing a PET with a spatial resolution less than the pixel size of the photosensor, such as a SiPM array.

点字ブロックを用いた移動ロボットの自律走行

It is difficult to know the self-position of the robot in a crowded environment. We use braille blocks as one way to navigate to the destination. The robot detects braille blocks using 3D sensor depth data. We consider them as a graph structure and autonomously navigate to the destination. There are common processing and induction block detector, warning block detector in the braille block detection processing. We use the Hough conversion in induction block detector, and clustering in warning block detector. As a result of the detection experiment, the detection rate was about 70%. We confirmed that we can navigate the robot to the destination by using the detector.

Four channel Cosmic Ray detector based on polymaq

The Cherenkov radiation has been widely studied in transparent materials, and applied to detect and identify elementary particles. But it has not been widely studied in opaque materials. A four channels radiation detector has been designed, built, characterized, and operated; based on four polymaq (UHMW-PE) bars of 2.54 cm X 5.08 cm X 25.4 cm, which is an opaque material to visible radiation to the human eye. Silicon photo detectors, Hamamatsu, avalanche type (APD) are used to detect the radiation produced by the passage of particles in the detector blocks. The design, construction, characterization, operation, and preliminary results of this cosmic ray detector details are presented.

Performance of a 0.4 mm Pixelated Ce:GAGG Block Detector With Digital Silicon Photomultiplier

The intrinsic spatial resolution of the detector is an important aspect to reconstruct high quality nuclear medicine images. In order to realize a high spatial resolution, small pixelated Cerium doped Gd3Al2Ga3O12 (Ce:GAGG) scintillators–known for their high light output, high density and relatively fast decay time, were coupled to a digital silicon photomultiplier (dSiPM) for read out. This detector module consists of a $ {24 \times 24}$ Ce:GAGG scintillator block of 0.4 mm $ {\times }0.4$ mm $ {\times }5$ mm crystal elements and a 2 mm thick light guide made of acrylic resin. The digital silicon photomultiplier (dSiPM), DPC-3200-22-44, was used to acquire 2-D position histogram, energy resolution and coincidence timing resolution. The 2-dimensional position histogram of the Ce:GAGG block detector irradiated with 22Na gamma photons showed that most pixels were clearly resolved with an average peak-to-valley (P/V) ratio of ~3.4. The average energy resolution of the Ce:GAGG block detector was 17.8%. At trigger scheme 1 ( $ {1}^{\mathrm {st}}$ photon trigger), the coincidence timing resolution was 342 ± 7 ps FHWM when acquired in coincidence with a 2 mm $ {\times }2$ mm $ {\times }6$ mm LSO crystal (after skew correction). This study demonstrates that a pixelated Ce:GAGG block coupled with dSiPM provides good position performance and time resolution. We conclude that the highly pixelated Ce:GAGG detector module may be a good candidate for implementing ultrahigh resolution nuclear medicine systems and applications requiring good timing resolution.

Prompt Gamma Rays Detected With a BGO Block Compton Camera Reveal Range Deviations of Therapeutic Proton Beams

The dose deposition profile of protons is interesting for tumour treatment due to the increased ionization density at the end of their track. However, the inaccurate knowledge of the proton stopping point limits the precision of the therapy. Prompt gamma rays, a by-product of the irradiation, are candidates for an indirect measurement of the particle range. Compton cameras have been proposed for prompt gamma ray imaging, but struggle with high trigger rates and low coincident efficiency. The feasibility in a clinical environment has yet to be proved. At Universitats Protonen Therapie Dresden, two bismuth germanate (BGO) block detectors arranged face-to-face are deployed for imaging tests with a homogeneous target irradiated by a proton pencil beam. Shifts of the target, increase of its thickness and beam energy variation experiments are conducted. Each measurement lasts about 15 minutes at a low proton beam current. The effect of one centimetre proton range deviations on the backprojected images is analysed. The number of valid Compton events as well as the trigger rate expected in a realistic treatment plan with pencil beam scanning are estimated. The results support the use of a high density material despite its moderate energy resolution, in order to maximize the coincident efficiency. Nevertheless, they discourage the applicability of a two-plane Compton camera in a clinical scenario with usual beam currents.

Photomultipliers With the Screening Grid at the Anode for TOF PET Block Detectors

In spite of the excellent performance of SiPMs in the application of time-of-flight PET detectors, the development of better photomultipliers for PET detectors is still worth considering. Fast timing with detectors based on the PMT light readout depends mainly on the time jitter and the quantum efficiency of the PMTs. Several studies in the past showed that a screening grid at the anode significantly improves the time resolution when measured with scintillation detectors. ADIT Co. has started a development of a 1” diameter fast PMT with the screening grid at the anode to be applied in the block detectors in TOF PET scanners. In the presented studies, we report the first comparative study of the L25, a classical PMT, with one that is equipped with a screening grid. Adding the screening grid yielded a large improvement in the time resolution, up to a factor of 1.2.

An Event-Based Neurobiological Recognition System with Orientation Detector for Objects in Multiple Orientations.

A new multiple orientation event-based neurobiological recognition system is proposed by integrating recognition and tracking function in this paper, which is used for asynchronous address-event representation (AER) image sensors. The characteristic of this system has been enriched to recognize the objects in multiple orientations with only training samples moving in a single orientation. The system extracts multi-scale and multi-orientation line features inspired by models of the primate visual cortex. An orientation detector based on modified Gaussian blob tracking algorithm is introduced for object tracking and orientation detection. The orientation detector and feature extraction block work in simultaneous mode, without any increase in categorization time. An addresses lookup table (addresses LUT) is also presented to adjust the feature maps by addresses mapping and reordering, and they are categorized in the trained spiking neural network. This recognition system is evaluated with the MNIST dataset which have played important roles in the development of computer vision, and the accuracy is increased owing to the use of both ON and OFF events. AER data acquired by a dynamic vision senses (DVS) are also tested on the system, such as moving digits, pokers, and vehicles. The experimental results show that the proposed system can realize event-based multi-orientation recognition. The work presented in this paper makes a number of contributions to the event-based vision processing system for multi-orientation object recognition. It develops a new tracking-recognition architecture to feedforward categorization system and an address reorder approach to classify multi-orientation objects using event-based data. It provides a new way to recognize multiple orientation objects with only samples in single orientation.

Crystal Identification in Dual-Layer-Offset DOI-PET Detectors Using Stratified Peak Tracking Based on SVD and Mean-Shift Algorithm

An Anger-logic based pixelated PET detector block requires a crystal position map (CPM) to assign the position of each detected event to a most probable crystal index. Accurate assignments are crucial to PET imaging performance. In this paper, we present a novel automatic approach to generate the CPMs for dual-layer offset (DLO) PET detectors using a stratified peak tracking method. In which, the top and bottom layers are distinguished by their intensity difference and the peaks of the top and bottom layers are tracked based on a singular value decomposition (SVD) and mean-shift algorithm in succession. The CPM is created by classifying each pixel to its nearest peak and assigning the pixel with the crystal index of that peak. A Matlab-based graphical user interface program was developed including the automatic algorithm and a manual interaction procedure. The algorithm was tested for three DLO PET detector blocks. Results show that the proposed method exhibits good performance as well as robustness for all the three blocks. Compared to the existing methods, our approach can directly distinguish the layer and crystal indices using the information of intensity and offset grid pattern.

Development of a PET/OMRI combined system for simultaneous imaging of positron and free radical probes for small animals.

Positron emission tomography (PET) has high sensitivity for imaging radioactive tracer distributions in subjects. However, it is not possible to image free radical distribution in a subject by PET. Since free radicals are quite reactive, they are related to many diseases, including but not limited to cancer, inflammation, strokes, and heart disease. The Overhauser enhanced magnetic resonance imaging (OMRI) is so far the only method that images free radical distribution in vivo. By combining PET and OMRI, a new hybrid imaging modality might be developed that can simultaneously image the radioactive tracer and free radical distributions. For this purpose, the authors developed a PET/OMRI combined system for small animals. The developed PET/OMRI system used an optical fiber-based PET system combined with a permanent magnet-based OMRI system. The optical fiber-based PET system uses flexible optical fiber bundles. Eight optical fiber-based block detectors were arranged in a 56 mm diameter ring to form a PET system. The LGSO blocks were located inside the field-of-view (FOV) of the OMRI, and the position sensitive photomultiplier tubes were positioned behind the OMRI to minimize the interference between the PET and the OMRI. The OMRI system used a 0.0165 T permanent magnet. The system has an electron spin resonance coil to enhance the MRI signal using the Overhauser effect to image the free radical in the FOV of the PET/OMRI system. The spatial resolution and sensitivity of the optical fiber-based PET system were 1.2 mm FWHM and 1.2% at the central FOV, respectively. The OMRI system imaged the distribution of a nitroxyl radical (NXR) solution. The interference between PET and OMRI was small. Simultaneous imaging of the positron radiotracer and the NXR solution was successfully conducted with the developed PET/OMRI system for phantom and small animal studies. The authors developed a PET/OMRI combined system with the potential to provide interesting new results in molecular imaging research, such as in vivo molecular and free radical distributions.

Experimental evaluation of the resolution improvement provided by a silicon PET probe

A high-resolution PET system, which incorporates a silicon detector probe into a conventional PET scanner, has been proposed to obtain increased image quality in a limited region of interest. Detailed simulation studies have previously shown that the additional probe information improves the spatial resolution of the reconstructed image and increases lesion detectability, with no cost to other image quality measures. The current study expands on the previous work by using a laboratory prototype of the silicon PET-probe system to examine the resolution improvement in an experimental setting. Two different versions of the probe prototype were assessed, both consisting of a back-to-back pair of 1-mm thick silicon pad detectors, one arranged in 32 × 16 arrays of 1.4 mm × 1.4 mm pixels and the other in 40 × 26 arrays of 1.0 mm × 1.0 mm pixels. Each detector was read out by a set of VATAGP7 ASICs and a custom-designed data acquisition board which allowed trigger and data interfacing with the PET scanner, itself consisting of BGO block detectors segmented into 8 × 6 arrays of 6 mm × 12 mm × 30 mm crystals. Limited-angle probe data was acquired from a group of Na-22 point-like sources in order to observe the maximum resolution achievable using the probe system. Data from a Derenzo-like resolution phantom was acquired, then scaled to obtain similar statistical quality as that of previous simulation studies. In this case, images were reconstructed using measurements of the PET ring alone and with the inclusion of the probe data. Images of the Na-22 source demonstrated a resolution of 1.5 mm FWHM in the probe data, the PET ring resolution being approximately 6 mm. Profiles taken through the image of the Derenzo-like phantom showed a clear increase in spatial resolution. Improvements in peak-to-valley ratios of 50% and 38%, in the 4.8 mm and 4.0 mm phantom features respectively, were observed, while previously unresolvable 3.2 mm features were brought to light by the addition of the probe. These results support the possibility of improving the image resolution of a clinical PET scanner using the silicon PET-probe.

Development of ultrahigh resolution Si-PM-based PET system using 0.32 mm pixel scintillators

Ultrahigh resolution small animal PET systems require small pixel size scintillators. We developed an ultrahigh resolution small animal PET system using fine LYSO pixels, which were 0.32mm×0.5mm×5.0mm. The LYSO pixels were combined into a 22×15 matrix with a 0.1mm thick BaSO4 reflector between them. The LYSO block was 9.24mm×9.0mm×5mm, and it was optically coupled to a 4×4 through silicon via silicon photomultiplier (TSV Si-PM) array that has smaller gaps between channels with a 1-mm thick light guide. We made eight Si-PM-based block detectors and arranged them octagonally to form a PET detector ring. At the center, the spatial resolution of the developed PET system, which was reconstructed by filtered back projection (FBP), was 0.6-mm FWHM. The sensitivity at the axial center was 0.5%. The peak noise equivalent count rate (NECR) was 12.5k cps. We obtained high resolution images of phantoms and small animals with the developed PET system. With these results, we conclude that a high resolution PET system is possible with 0.32mm pixel LYSO scintillators.

In-beam PET at clinical proton beams with pile-up rejection

Positron emission tomography (PET) is a means of imaging the β+-activity produced by the radiation field in ion beam therapy and therefore for treatment verification. Prompt γ-rays that are emitted during beam application challenge the detectors and electronics of PET systems, since those are designed for low and medium count rates. Typical PET detectors operated according to a modified Anger principle suffer from multiple events at high rates. Therefore, in-beam PET systems using such detectors rely on a synchronization of beam status and measurement to reject deteriorated data.In this work, a method for pile-up rejection is applied to conventional Anger logic block detectors. It allows for an in-beam data acquisition without further synchronization.Though cyclotrons produce a continuous wave beam, the radiation field shaping technique introduces breaks in the application. Time regimes mimicking synchrotrons as well as cyclotron based ones using double-scattering or pencil beam scanning field shaping at dose rates of 0.5, 1.0 and 2.0Gy/min were investigated. Two types of inhomogeneous phantoms were imaged. The first one simulates cavity structures, the other one mimics a static lung irradiation.It could be shown that, depending on the dose rate and the beam time structure, in-beam measurement including a few seconds decay time only, yield images which revealed all inhomogeneities in the phantoms. This technique can be the basis for the development of an in-beam PET system with traditional detectors and off-the-shelf electronics.

Evaluation of PeneloPET Simulations of Biograph PET/CT Scanners

Monte Carlo (MC) simulations are widely used in positron emission tomography (PET) for optimizing detector design, acquisition protocols, and evaluating corrections and reconstruction methods. PeneloPET is a MC code based on PENELOPE, for PET simulations which considers detector geometry, acquisition electronics and materials, and source definitions. While PeneloPET has been successfully employed and validated with small animal PET scanners, it required a proper validation with clinical PET scanners including time-of-flight (TOF) information. For this purpose, we chose the family of Biograph PET/CT scanners: the Biograph True-Point (B-TP), Biograph True-Point with TrueV (B-TPTV) and the Biograph mCT. They have similar block detectors and electronics, but a different number of rings and configuration. Some effective parameters of the simulations, such as the dead-time and the size of the reflectors in the detectors, were adjusted to reproduce the sensitivity and noise equivalent count (NEC) rate of the B-TPTV scanner. These parameters were then used to make predictions of experimental results such as sensitivity, NEC rate, spatial resolution, and scatter fraction (SF), from all the Biograph scanners and some variations of them (energy windows and additional rings of detectors). Predictions agree with the measured values for the three scanners, within 7% (sensitivity and NEC rate) and 5% (SF). The resolution obtained for the B-TPTV is slightly better (10%) than the experimental values. In conclusion, we have shown that PeneloPET is suitable for simulating and investigating clinical systems with good accuracy and short computational time, though some effort tuning of a few parameters of the scanners modeled may be needed in case that the full details of the scanners studied are not available.

A High Temperature Frequency Signal Conditioning Unit for Aeronautical Rotating Systems

This paper covers the development and testing of a high temperature signal conditioning unit capable of sensing wide dynamic range signals from rotating sensors. The unit includes a current peak detector block, a digital pulse generator, ESD (electrostatic discharge) protection and generates an output current proportional to the peak value of the applied input signal. The digital data from the unit can be directly utilized by the FADEC (Full Authority Digital Electronic Control) system or the EHMS (Engine Health Monitoring System) on an aeroengine. The mixed signal unit presented in this paper was designed and fabricated on 1 $\mu\text{m}$ silicon-on-insulator (SOI) CMOS (complementary metal oxide semiconductor) technology and has been shown to function up to 235 $^{\circ}$ Celsius with very high linearity of the output signal. This is the highest operating temperature of an integrated signal conditioning unit developed for a civil aircraft. The mixed signal unit was mounted on a high temperature hybrid module and helps reducing the weight of the aeroengine by several kilograms.

Performance evaluation of neuro-PET using silicon photomultipliers

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 511keV gamma rays were 17±0.1% and 3±0.3ns, respectively. Spatial resolution and sensitivity at the center of field of view (FOV) were 3.1mm and 0.8%, respectively. The average scatter fraction was 0.4 with an energy window of 350–650keV. The maximum true count rate and maximum NECR were measured as 43.3kcps and 6.5kcps at an activity concentration of 16.7kBq/ml and 5.5kBq/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.

Sub-millimetre DOI detector based on monolithic LYSO and digital SiPM for a dedicated small-animal PET system

The mouse model is widely used in a vast range of biomedical and preclinical studies. Thanks to the ability to detect and quantify biological processes at the molecular level in vivo, PET has become a well-established tool in these investigations. However, the need to visualize and quantify radiopharmaceuticals in anatomic structures of millimetre or less requires good spatial resolution and sensitivity from small-animal PET imaging systems.In previous work we have presented a proof-of-concept of a dedicated high-resolution small-animal PET scanner based on thin monolithic scintillator crystals and Digital Photon Counter photosensor. The combination of thin monolithic crystals and MLE positioning algorithm resulted in an excellent spatial resolution of 0.7 mm uniform in the entire field of view (FOV). However, the limitation of the scanner was its low sensitivity due to small thickness of the lutetium-yttrium oxyorthosilicate (LYSO) crystals (2 mm).Here we present an improved detector design for a small-animal PET system that simultaneously achieves higher sensitivity and sustains a sub-millimetre spatial resolution. The proposed detector consists of a 5 mm thick monolithic LYSO crystal optically coupled to a Digital Photon Counter. Mean nearest neighbour (MNN) positioning combined with depth of interaction (DOI) decoding was employed to achieve sub-millimetre spatial resolution. To evaluate detector performance the intrinsic spatial resolution, energy resolution and coincidence resolving time (CRT) were measured. The average intrinsic spatial resolution of the detector was 0.60 mm full-width-at-half-maximum (FWHM). A DOI resolution of 1.66 mm was achieved. The energy resolution was 23% FWHM at 511 keV and CRT of 529 ps were measured. The improved detector design overcomes the sensitivity limitation of the previous design by increasing the nominal sensitivity of the detector block and retains an excellent intrinsic spatial resolution.