Monolithic Crystals Research Articles

Porous Single-Crystal Nitrides for Enhanced Pseudocapacitance and Stability in Energy Storage Applications.

Supercapacitors have emerged as a prominent area of research in energy storage technology, primarily because of their high power density and notable stability compared to batteries. However, their practical implementation is hindered by their low energy densities and insufficient long-term stability. In this study, bulk porous Nb4N5 and Ta3N5 single crystals with excellent pseudocapacitance and electrical conductivity are successfully prepared by solid-phase transformation method. These monolithic porous single crystals (PSC) exhibit a long-range ordered crystalline architecture and substantial specific surface area, which facilitate rapid charge transport and ion diffusion within the electrolyte-permeated crystal lattice. Notably, the areal capacitance of the porous Nb4N5 single crystals is 12.9 F cm-2 at a current density of 6mA cm-2 and 35.08 F cm-2 at a scan rate of 1mV s-1. Furthermore, the energy density reached 1.79 mWh cm-2 at a power density of 20mW cm-2, demonstrating their high energy storage capability. Moreover, these porous Nb4N5 single crystals exhibited robust capacitance retention and exceptional cycling stability, making them promising candidates for use as electrodes in energy storage applications. These results underscore the significant potential of porous metal nitride single crystals in advancing the field of capacitive energy storage.

Compact 2-μm Hundred Hertz optical parametric oscillator Based on KTP crystal

A 100 Hz compact 2 μm optical parametric oscillator (OPO) based on a type II non-critically phase-matched KTiOPO4 crystal (KTP) was reported. The monolithic KTP crystal was pumped with a passively Q-switched 1064 nm Nd:YAG laser. At a repetition rate of 100 Hz and a single pulse energy of 5.8 mJ of pump light, a 2128-nm laser output was achieved with a maximum of 1.17 mJ of parametric light at the degenerate point, with a parametric light pulse width of approximately 10.5 ns, corresponding to a pump to parametric light conversion efficiency of 20.1 %.

Multichannel SiPM test readout system for gamma ray measurements with monolithic inorganic CeBr3

Abstract Energy resolution and the detection efficiency for gamma quanta are fundamental properties in the construction of detectors for ionizing radiation. In this study, a SiPM-based photodetector coupled to a monolithic inorganic CeBr3 crystal is exposed to gamma rays in order to study the performance of the CeBr3 crystal. Measurements are made using three different radioactive sources - 137Cs, 22Na and 60Co. For each source, the measurements are made using a few different values for the Bias voltage of the SiPM. Furthermore, two CeBr3 crystals with different thicknesses are used in order to study how detector efficiency is affected by crystal dimensions. A preliminary analysis of the data is presented.

A study on “position-energy” response correction method based on monolithic crystal coupled SiPM array

A study on “position-energy” response correction method based on monolithic crystal coupled SiPM array

Effects of void geometry on two-dimensional monolithic porous phononic crystals

Phononic crystals are renowned for their distinctive wave propagation characteristics, notably bandgaps that offer precise control over vibration phenomena, positioning them as a critical material in advanced vibro-elastic engineering and design. We investigate how pore shapes influence the bandgap in continuum two-dimensional phononic crystals made from a single material. Using the square lattice and unit cells with fourfold symmetry, our numerical analyses reveal that the normalized gap size is highly dependent on the minimum ligament width in the structure. Additionally, we find that fine geometric features represented by higher-order Fourier coefficients decrease the gap size. This study offers insight into the design of phononic crystals and vibro-elastic metamaterials for precise wave control through void patterning.

Crystal scatter effects in a large-area dual-panel Positron Emission Mammography system.

Positron Emission Mammography (PEM) is a valuable molecular imaging technique for breast studies using pharmaceuticals labeled with positron emitters and dual-panel detectors. PEM scanners normally use large scintillation crystals coupled to sensitive photodetectors. Multiple interactions of the 511 keV annihilation photons in the crystals can result in event mispositioning leading to a negative impact in radiopharmaceutical uptake quantification. In this work, we report the study of crystal scatter effects of a large-area dual-panel PEM system designed with either monolithic or pixelated lutetium yttrium orthosilicate (LYSO) crystals using the Monte Carlo simulation platform GATE. The results show that only a relatively small fraction of coincidences (~20%) arise from events where both coincidence photons undergo single interactions (mostly through photoelectric absorption) in the crystals. Most of the coincidences are events where at least one of the annihilation photons undergoes a chain of Compton scatterings: approximately 79% end up in photoelectric absorption while the rest (<1%) escape the detector. Mean positioning errors, calculated as the distance between first hit and energy weighted (assigned) positions of interaction, were 1.70 mm and 1.92 mm for the monolithic and pixelated crystals, respectively. Reconstructed spatial resolution quantification with a miniDerenzo phantom and a list mode iterative reconstruction algorithm shows that, for both crystal types, 2 mm diameter hot rods were resolved, indicating a relatively small effect in spatial resolution. A drastic reduction in peak-to-valley ratios for the same hot-rod diameters was observed, up to a factor of 14 for the monolithic crystals and 7.5 for the pixelated ones.

Monolithic PMN-39PT nanograting-assisted second harmonic generation enhancement.

Second harmonic generation plays a vital role in frequency conversion which mutually promotes the laser technology and allows the wavebands extension of new coherent source. The monolithic crystals are supposed to be a superior choice for harmonic generation due to long interaction distance, however, the phase-mismatch brought a sharp reduction in the conversion efficiency. Although birefringent phase-matching and quasi-phase-matching techniques are commonly utilized to fill the phase gap in monolithic crystals, these techniques are limited by the natural refractive index of crystal and the domain engineering, respectively. In recent years, subwavelength structures evolve as a flexible scheme to realize phase matching by engineering the geometry features of crystals. Here, structured nanogratings are designed and fabricated on a monolithic PMN-39PT (Pb(Mg1/3Nb2/3)O3-0.39PbTiO3) substrate, a novel ferroelectric crystal with promising optical prospect, for enhancing second harmonic generation, where birefringent or quasi phase-matching is hard to achieve. The nanograting-assisted second harmonic generation enhancement is observed which is not limited by the availability of thin crystalline films. Meanwhile, a boost in the second harmonic signal synchronously promotes the cascading third harmonic generation. This method may provide an alternative solution for enhanced harmonic generation on monolithic substrates and develop potential nonlinear optical materials for frequency conversion.

A finely segmented semi-monolithic detector tailored for high-resolution PET.

Preclinical research and organ-dedicated applications use and require high (spatial-)resolution positron emission tomography (PET) detectors to visualize small structures (early) and understand biological processes at a finer level of detail. Researchers seeking to improve detector and image spatial resolution have explored various detector designs. Current commercial high-resolution systems often employ finely pixelated or monolithic scintillators, each with its limitations. We present a semi-monolithic detector, tailored for high-resolution PET applications with a spatial resolution in the range of 1mm or better, merging concepts of monolithic and pixelated crystals. The detector features LYSO slabs measuring (24×10×1)mm3, coupled to a 12×12 readout channel photosensor with 4mm pitch. The slabs are grouped in two arrays of 44 slabs each to achieve a higher optical photon density despite the fine segmentation. We employ a fan beam collimator for fast calibration to train machine-learning-based positioning models for all three dimensions, including slab identification and depth-of-interaction (DOI), utilizing gradient tree boosting (GTB). The data for all dimensions was acquired in less than 2h. Energy calculation was based on a position-dependent energy calibration. Using an analytical timing calibration, time skews were corrected for coincidence timing resolution (CTR) estimation. Leveraging machine-learning-based calibration in all three dimensions, we achieved high detector spatial resolution: down to 1.18mm full width at half maximum (FWHM) detector spatial resolution and 0.75mm mean absolute error (MAE) in the planar-monolithic direction, and 2.14mm FWHM and 1.03mm MAE for DOI at an energy window of (435-585)keV. Correct slab interaction identification in planar-segmented direction exceeded 80%, alongside an energy resolution of 12.7% and a CTR of 450ps FWHM. The introduced finely segmented, high-resolution slab detector demonstrates appealing performance characteristics suitable for high-resolution PET applications. The current benchtop-based detector calibration routine allows these detectors to be used in PET systems.

A facile synthesis of monolithic MOF single crystal for gas separation via a supersaturation strategy

Large-area metal–organic framework (MOF) single crystal membrane materials hold great appeal in gas separation field due to their outstanding separation selectivity and permeability. Nevertheless, it is currently difficult to prepare MOF single crystals large enough for gas separation tests owing to the limited manufacturing processes. In this work, we fabricate a self-supporting MOF single crystal (Co-btec SC) membrane with 0.3 × 0.1 cm2 dimension via a facile supersaturation synthesis strategy. Benefiting from the one-dimensional (1D) transmission pathway and three-dimensional (3D) connection network, the obtained Co-btec SC has ultra-high permeability of 47,647 Barrer. Besides, the H2O molecules firmly filled in the pore channels greatly improve the affinity and solubility for CO2, and thus Co-btec SC yields CO2 preferential permeation in CO2/H2 mixture with superior CO2/H2 selectivity of 18.79. In addition, the Co-btec SC shows dramatic high-temperature and high-humidity separation stabilities. To demonstrate the versatility of this strategy, we also successfully fabricated hydrogen-bonded organic framework single crystals (HOF SCs) with the size of about 0.4 cm. This supersaturation strategy opens a new way to fabricate the large-area MOF single crystal membranes.

Opto-microfluidic coupling between optical waveguides and tilted microchannels in lithium niobate.

This work presents a reconfigurable opto-microfluidic coupling between optical waveguides and tilted microfluidic channels in monolithic lithium niobate crystal. The light path connecting two waveguide arrays located on opposite sides of a microfluidic channel depends on the refractive index between the liquid phase and the hosting crystal. As a result, the optical properties of the flowing fluid, which is pumped into the microfluidic channel on demand, can be exploited to control the light pathways inside the optofluidic device. Proof-of-concept applications are herein presented, including microfluidic optical waveguide switching, optical refractive index sensing, and wavelength demultiplexing.

Influence of the background in Compton camera images for proton therapy treatment monitoring

Objective. Background events are one of the most relevant contributions to image degradation in Compton camera imaging for hadron therapy treatment monitoring. A study of the background and its contribution to image degradation is important to define future strategies to reduce the background in the system. Approach. In this simulation study, the percentage of different kinds of events and their contribution to the reconstructed image in a two-layer Compton camera have been evaluated. To this end, GATE v8.2 simulations of a proton beam impinging on a PMMA phantom have been carried out, for different proton beam energies and at different beam intensities. Main results. For a simulated Compton camera made of Lanthanum (III) Bromide monolithic crystals, coincidences caused by neutrons arriving from the phantom are the most common type of background produced by secondary radiations in the Compton camera, causing between 13% and 33% of the detected coincidences, depending on the beam energy. Results also show that random coincidences are a significant cause of image degradation at high beam intensities, and their influence in the reconstructed images is studied for values of the time coincidence windows from 500 ps to 100 ns. Significance. Results indicate the timing capabilities required to retrieve the fall-off position with good precision. Still, the noise observed in the image when no randoms are considered make us consider further background rejection methods.

Monte Carlo simulation of the system performance of a long axial field-of-view PET based on monolithic LYSO detectors

BackgroundIn light of the milestones achieved in PET design so far, further sensitivity improvements aim to optimise factors such as the dose, throughput, and detection of small lesions. While several longer axial field-of-view (aFOV) PET systems based on pixelated detectors have been installed, continuous monolithic scintillation detectors recently gained increased attention due to their depth of interaction capability and superior intrinsic resolution. As a result, the aim of this work is to present and evaluate the performance of two long aFOV, monolithic LYSO-based PET scanner designs.MethodsGeant4 Application for Tomographic Emission (GATE) v9.1 was used to perform the simulations. Scanner designs A and B have an aFOV of 36.2 cm (7 rings) and 72.6 cm (14 rings), respectively, with 40 detector modules per ring each and a bore diameter of 70 cm. Each module is a 50 × 50 × 16 mm3 monolithic LYSO crystal. Sensitivity, noise equivalent count rate (NECR), scatter fraction, spatial resolution, and image quality tests were performed based on NEMA NU-2018 standards.ResultsThe sensitivity of design A was calculated to be 29.2 kcps/MBq at the centre and 27 kcps/MBq at 10 cm radial offset; similarly, the sensitivity of design B was found to be 106.8 kcps/MBq and 98.3 kcps/MBq at 10 cm radial offset. NECR peaks were reached at activity concentrations beyond the range of activities used for clinical studies. In terms of spatial resolution, the values for the point sources were below 2 mm for the radial, tangential, and axial full width half maximum. The contrast recovery coefficient ranged from 53% for design B and 4:1 contrast ratio to 90% for design A and 8:1 ratio, with a reasonably low background variability.ConclusionsLonger aFOV PET designs using monolithic LYSO have superior spatial resolution compared to current pixelated total-body PET (TB-PET) scanners. These systems combine high sensitivity with improved contrast recovery.

Optimization of Variable Parameters in Diode Pumped SHG Nd-YAG Lasers

Second Harmonic Generation (SHG) produces many parameters which are the consequences of interaction of fundamental incident power &nbsp;and those created inside the second harmonic cavity, external employing monolithic crystals. In this study, a low power of &nbsp;continuous wave (CW) Nd-YAG laser with principal output of &nbsp;and maximum power of &nbsp;theoretically was used. The crystal is [MgO: LiNbO3] which is lithium niobate, magnesium oxide doped with specific optical properties explained, the parameters in questions are both reflection &nbsp;and circulating &nbsp;powers in the second harmonic cavity. Both are functions of fundamental incident power . The results are compared with their experimental correspondents and interpretation for the causes is discussed.

Characterization of Experimental Nanoparticulated Dental Adhesive Resins with Long-Term Antibacterial Properties.

Experimental adhesives with functional nitrogen-doped titanium dioxide nanoparticles (N_TiO2) have been shown to display improved properties. However, these materials have not been characterized regarding their degree of conversion (DC), biaxial flexure strength (BFS), surface roughness (SR), elastic modulus (EM), and long-term antibacterial functionalities. Experimental adhesives were synthesized by dispersing N_TiO2 (10%, 20%, or 30%, v/v%) into OptiBond Solo Plus (OPTB, Kerr Corp., USA). Unpolymerized adhesives (volume = 50 μL/drop, n = 3/group) were individually placed onto a heated (37 °C) attenuated total reflectance (ATR) monolithic diamond crystal (Golden Gate, Specac). The spectra of composites were obtained with a Fourier-transform infrared (FTIR) spectrometer (Nicolet IS50; 500-4500 cm-1; resolution = 4 cm-1, 10 internal scans/spectrum) before and after polymerization. Disk-shaped specimens (diameter = 6.0 mm, thickness = 0.5 mm) for BFS (n = 12/group), SR and EM (n = 3/group), and for antibacterial testing (n = 18/group/time-point) were fabricated and photopolymerized (1 min each; 385-515 nm, 1000 mW/cm2; VALO). DC values (%) were calculated from pre- and post-polymerization spectra using the two-frequency method and tangent-baseline technique. BFS was assessed using a universal testing machine (Instron 68TM-5, crosshead speed = 1.27 mm/min, 25 °C). SR and EM were investigated using an atomic force microscope (Multimode 8) with aluminum-coated silicon probes (8 nm pyramidal tip, spring constant 40 N/m, Bruker). Antibacterial testing was performed by growing Streptococcus mutans biofilms (UA159-ldh, 37 °C, microaerophilic) on the surfaces of specimens for 24 h and then measuring the relative luminescence units (RLU) with a Biotek Synergy HT multi-well plate reader. Results demonstrate that experimental materials containing 10%, 20%, and 30% of N_TiO2 displayed higher levels of DC, had better mechanical properties, and were able to exert strong and durable antibacterial properties without visible light irradiation and after extended periods of simulated shelf-life and aging in PBS. The reported experimental materials are expected to increase the service lives of polymer-based bonded restorations by decreasing the incidence of secondary caries.

A study on a nonlinear least-squares fitting method for 3D positioning of gamma rays based on monolithic crystal and SiPM array

A study on a nonlinear least-squares fitting method for 3D positioning of gamma rays based on monolithic crystal and SiPM array

A neural network-based algorithm for simultaneous event positioning and timestamping in monolithic scintillators

Objective. Monolithic scintillator crystals coupled to silicon photomultiplier (SiPM) arrays are promising detectors for PET applications, offering spatial resolution around 1 mm and depth-of-interaction information. However, their timing resolution has always been inferior to that of pixellated crystals, while the best results on spatial resolution have been obtained with algorithms that cannot operate in real-time in a PET detector. In this study, we explore the capabilities of monolithic crystals with respect to spatial and timing resolution, presenting new algorithms that overcome the mentioned problems. Approach. Our algorithms were tested first using a simulation framework, then on experimentally acquired data. We tested an event timestamping algorithm based on neural networks which was then integrated into a second neural network for simultaneous estimation of the event position and timestamp. Both algorithms are implemented in a low-cost field-programmable gate array that can be integrated in the detector and can process more than 1 million events per second in real-time. Results. Testing the neural network for the simultaneous estimation of the event position and timestamp on experimental data we obtain 0.78 2D FWHM on the (x, y) plane, 1.2 depth-of-interaction FWHM and 156 coincidence time resolution on a LYSO monolith read-out by 64 Hamamatsu SiPMs. Significance. Our results show that monolithic crystals combined with artificial intelligence can rival pixellated crystals performance for time-of-flight PET applications, while having better spatial resolution and DOI resolution. Thanks to the use of very light neural networks, event characterization can be done on-line directly in the detector, solving the issues of scalability and computational complexity that up to now were preventing the use of monolithic crystals in clinical PET scanners.

Performance evaluation of side-by-side optically coupled monolithic LYSO crystals.

BackgroundSignificant interest has been recently shown for using monolithic scintillation crystals in molecular imaging systems, such as positron emission tomography (PET) scanners. Monolithic‐based PET scanners result in a lower cost and higher sensitivity, in contrast to systems based on the more conventional pixellated configuration. The monolithic design allows one to retrieve depth‐of‐interaction information of the impinging 511 keV photons without the need for additional hardware materials or complex positioning algorithms. However, the so‐called edge‐effect inherent to monolithic‐based approaches worsens the detector performance toward the crystal borders due to the truncation of the light distribution, thus decreasing positioning accuracy.PurposeThe main goal of this work is to experimentally demonstrate the detector performance improvement when machine‐learning artificial neural‐network (NN) techniques are applied for positioning estimation in multiple monolithic scintillators optically coupled side‐by‐side.MethodsIn this work, we show the performance evaluation of two LYSO crystals of 33 × 25.4 × 10 mm3 optically coupled by means of a high refractive index adhesive compound (Meltmount, refractive index n = 1.70). A 12 × 12 silicon photomultiplier array has been used as photosensor. For comparison, the same detector configuration was tested for two additional coupling cases: (1) optical grease (n = 1.46) in between crystals, and (2) isolated crystals using black paint with an air gap at the interface (named standard configuration). Regarding 2D photon positioning (XY plane), we have tested two different methods: (1) a machine‐learning artificial NN algorithm and (2) a squared‐charge (SC) centroid technique.ResultsAt the interface region of the detector, the SC method achieved spatial resolutions of 1.7 ± 0.3, 2.4 ± 0.3, and 2.6 ± 0.4 mm full‐width at half‐maximum (FWHM) for the Meltmount, grease, and standard configurations, respectively. These values improve to 1.0 ± 0.2, 1.2 ± 0.2, and 1.2 ± 0.3 mm FWHM when the NN algorithm was employed. Regarding energy performance, resolutions of 18 ± 2%, 20 ± 2%, and 23 ± 3% were obtained at the interface region of the detector for Meltmount, grease, and standard configurations, respectively.ConclusionsThe results suggest that optically coupling together scintillators with a high refractive index adhesive, in combination with an NN algorithm, reduces edge‐effects and makes it possible to build scanners with almost no gaps in between detectors.

Simulation study on 3D convolutional neural networks for time-of-flight prediction in monolithic PET detectors using digitized waveforms

Objective. We investigate the use of 3D convolutional neural networks for gamma arrival time estimation in monolithic scintillation detectors. Approach. The required data is obtained by Monte Carlo simulation in GATE v8.2, based on a 50 × 50 × 16 mm3 monolithic LYSO crystal coupled to an 8 × 8 readout array of silicon photomultipliers (SiPMs). The electronic signals are simulated as a sum of bi-exponentional functions centered around the scintillation photon detection times. We include various effects of statistical fluctuations present in non-ideal SiPMs, such as dark counts and limited photon detection efficiency. The data was simulated for two distinct overvoltages of the SensL J-Series 60 035 SiPMs, in order to test the effects of different SiPM parameters. The neural network uses the array of detector waveforms, digitized at 10 GS s−1, to predict the time at which the gamma arrived at the crystal. Main results. Best results were achieved for an overvoltage of +6 V, at which point the SiPM reaches its optimal photon detection efficiency, resulting in a coincidence time resolution (CTR) of 141 ps full width at half maximum (FWHM). It is a 26% improvement compared to a simple averaging of the first few SiPM timestamps obtained by leading edge discrimination, which in comparison produced a CTR of 177 ps FWHM. In addition, better detector uniformity was achieved, although some degradation near the corners did remain. Significance. These improvements in time resolution can lead to higher signal-to-noise ratios in time-of-flight positron emission tomography, ultimately resulting in better diagnostic capabilities.

Concept development of an on-chip PET system

BackgroundOrgans-on-Chips (OOCs), microdevices mimicking in vivo organs, find growing applications in disease modeling and drug discovery. With the increasing number of uses comes a strong demand for imaging capabilities of OOCs as monitoring physiologic processes within OOCs is vital for the continuous improvement of this technology. Positron Emission Tomography (PET) would be ideal for OOC imaging, however, current PET systems are insufficient for this task due to their inadequate spatial resolution. In this work, we propose the concept of an On-Chip PET system capable of imaging OOCs and optimize its design using a Monte Carlo Simulation (MCS).Material and methodsThe proposed system consists of four detectors arranged around the OOC device. Each detector is made of two monolithic LYSO crystals and covered with Silicon photomultipliers (SiPMs) on multiple surfaces. We use a Convolutional Neural Network (CNN) trained with data from a MCS to predict the first gamma-ray interaction position inside the detector from the light patterns that are recorded by the SiPMs on the detector’s surfaces.ResultsThe CNN achieves a mean average prediction error of 0.80 mm in the best configuration. The proposed system achieves a sensitivity of 34.81% for 13 mm thick crystals and does not show a prediction degradation near the boundaries of the detector. We use the trained network to reconstruct an image of a grid of 21 point sources spread across the field-of-view and obtain a mean spatial resolution of 0.55 mm. We show that 25,000 Line of Responses (LORs) are needed to reconstruct a realistic OOC phantom with adequate image quality.ConclusionsWe demonstrate that it is possible to achieve a spatial resolution of almost 0.5 mm in a PET system made of multiple monolithic LYSO crystals by directly predicting the scintillation position from light patterns created with SiPMs. We observe that a thinner crystal performs better than a thicker one, that increasing the SiPM size from 3 mm to 6 mm only slightly decreases the prediction performance, and that certain surfaces encode significantly more information for the scintillation-point prediction than others.

Scintillation event localization in hemi-ellipsoid detector for SPECT, a simulation study using Geant4 Monte-Carlo

Purpose: a high sensitivity Cardiac SPECT system using curved crystals with pinhole collimation was proposed previously (Dey, IEEE Trans. Nucl. Sci. 59 (2012) 334). Using hemi-ellipsoid CsI crystals, in simulations, the system improved sensitivity by a factor of 3 over newer generation SPECT systems (DSPECT or GE Discovery) while keeping the resolution comparable (Bhusal et al., Med. Phys. 46 (2018) 116). In this work, we hypothesize that the high curvature detector results in measurable differences in light distribution from events at different depths in the crystal. We rigorously test this by analyzing the scintillation light using Monte-Carlo (Geant4) and propose a statistical event localization method in a hemi-ellipsoid detector. We evaluate the localization error of the algorithm and the back-projected errors in object space. Methods: to develop this localization capability for the proposed design, we used Geant4 to simulate the propagation of scintillation light in a monolithic hemi-ellipsoidal CsI crystal. A look-up table (LUT) was created to map the points inside the crystal to the expected light pattern on the crystal surface using the Geant4 simulation data. Thirteen zones were considered across the crystal. In each zone, gamma-rays were simulated and the resulting photon intensity on the surface was captured, serving as our experimental interactions. An algorithm based on Poisson statistics was developed to limit the search of the experimental gamma-ray event locations into smaller regions of the LUT. The localization was fine-tuned by comparing the light distribution of the gamma interactions in selected patterns from the LUT points and then recorded. The algorithm-localized gamma-ray events were also individually back-projected to the object mid-plane, (expected mid-plane of the heart), and the error at the plane was recorded as well. Results: the light patterns of adjacent LUT points showed visually discernible differences. Excluding some outliers (up to 2%), the localized errors averaged over all the zones was 0.71 (±0.44) mm with a worse case of 1.36 (± 0.67) mm at the apex. Moreover, when back-projected to the midplane of the region of interest for Cardiac SPECT, the errors were <1 mm due to the high system magnification afforded by the apex and other zones. The average back-projection error at the mid-plane of the object was 0.4 mm±0.22 mm. Conclusion: we modeled gamma-event interactions and scintillation light spread in CsI hemi-ellipsoid detector and developed a robust statistical algorithm that localized scintillation events to within 0.71 (±0.44) mm on the average within a hemi-ellipsoid CsI detector. Moreover, due to the high system magnification afforded by the crystal, the hemi-ellipsoid unit was capable of achieving <1 mm average localization in the object space, assuming perfect pinhole collimator resolution recovery. Thus, we show that this high sensitivity system will be able to deliver images with high resolution for Cardiac SPECT. In the future, the application of this may be extended to Brain SPECT and small animal imaging.