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We report on a small gamma spectrometer with directional detection, based on two modules. Each module contains an array of 128 scintillator pixels coupled to reverse-biased photodiodes, an ASIC and a microcontroller. Modules communicate via USB and are operated via an Android GUI on a WiFi-connected device. Transparent ceramic GYGAG ((Gd,Y,Ce)3(Ga,Al)5O12) garnet scintillator pixels offer energy resolution as good as 3.1% at 662 keV for individual pixels. We previously reported on an eight-module planar spectrometer, based on the same technology1. The current compact system uses two modules in a back-to-back configuration to improve its speed and accuracy in locating a gamma-emitting source in a 4-pi field of view. This dual module system (~2.5 x 2.5 x 3.5 inches) is suitable as a pager-sized RIID or spectroscopic personal radiation detector (SPRD). Multiple dual module units can be combined for improved efficiency. Spectroscopic and directional performance will be described.

We have developed a handheld $\gamma $ -ray spectrometer based on 1024 pixels, $2.8\,\,\text {mm} \times 2.8\,\,\text {mm} \times 6$ mm in size, of gadolinium–yttrium–gallium–aluminum garnet (GYGAG) ((Gd,Y,Ce)3(Ga,Al)5O12) ceramic scintillator (total of 48-cm3 detector volume) coupled to silicon photodiode (SiPD) arrays. The SiPD arrays and readout ASIC, originally developed for medical imaging applications, have been adapted for portability in a lightweight box with heatsink and thermoelectric cooling. Custom readout firmware for $\gamma $ -ray spectroscopy has been implemented, and a system user interface was developed that runs on an Android tablet. We have optimized the processing of the GYGAG(Ce), the pixel optical coupling, and electronics readout parameters to obtain single pixel energy resolution as good as $R (662\,\,\text {keV}) = 3.1$ % full-width at half-maximum and full device resolution with singles events from all pixels summed of 4.5%. When Compton-summed events are included, full-energy peak efficiency increases by $\sim 2\times $ , and $R (662\,\,\text {keV}) = 4.7$ % is obtained for the full device. The pixelated architecture is leveraged to locate point sources of radiological materials using Compton imaging and active masking techniques. Directional detection of a 1 mCi Cs-137 source at 10 m can be made to ±10° in ~2 s.

Inexpensive spectroscopic personal radiation detectors (SPRDs) are needed to monitor environmental radioactivity and search for sources. For gamma spectroscopy, excellent light yield, material uniformity, light yield proportionality, mechanical and environmental ruggedness can be achieved in polycrystalline ceramic oxide garnets. We are building a compact detector based on 14 cm3 of transparent ceramic garnet, formed into 256 pixels (3mm x 3mm x 6mm each) and mounted on two stacked silicon photodiode arrays. GYGAG(Ce) garnet transparent ceramics offer density = 5.8g/cm3, Zeff = 48, principal decay of

Gadolinium Garnet transparent ceramics doped with Ce, ((Gd,Y,Ce)3(Ga,Al)5O12), for gamma-ray spectroscopy provide high density, high light yield, high energy resolution , high Z, mechanical robustness, and they are unreactive to air and water. Gadolinium garnet single crystals are costly to grow, due to their high melting points, and suffer from non-uniform light yield, due to Ce segregation. In contrast, transparent polycrystalline ceramic Garnets are never melted, and therefore are less costly to produce and provide the uniform light yield required to achieve high energy resolution with a scintillator. GYGAG(Ce) transparent ceramics offer energy resolution as good as R(662 keV) = 3.5%, in a pixelated detector utilizing Silicon photodiode array readout. We have developed a modular handheld detector based on pixelated GYGAG(Ce) on a photodiode array, that offers directional detection for point source detection as well as gamma spectroscopy. Individual modules can be assembled into detectors ranging from pocket-size to large panels, for a range of applications. Large GYGAG(Ce) transparent ceramics in the 2-5 in3 size range have been fabricated at LLNL. Instrumentation of these ceramics with Silicon photomultipliers (SiPMs) and super bi-alkali PMTs has been explored and energy resolution as good as R(662 keV) = 5% has been obtained. Further improvements with SiPM readout will leverage their high quantum efficiency in the 500-650 nm range where GYGAG(Ce) emits, and implement electronics that minimize the effect of SiPM dark current and capacitance on the pulse height spectra. This work was performed under the auspices of the U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, and has been supported by the US Department of Homeland Security, Domestic Nuclear Detection Office, under competitively awarded IAA HSHQDC-12-X-00149 under Contract No. DE-AC03-76SF00098. LLNL-ABS-724480.

New transparent ceramic scintillators offer advantages for applications in gamma spectroscopy and X-ray imaging. For gamma spectroscopy, excellent light yield, material uniformity, light yield proportionality, mechanical and environmental ruggedness can be achieved in polycrystalline ceramic oxide garnets. We have fabricated 5 in3 Ce-doped Gd garnet transparent ceramics. GYGAG(Ce) garnet transparent ceramics offer $^{\mathbf {\rho \, =\, 5.8g/cm^{3},\,}}$, $z_{eff}=48$, principal decay of 2 O 3 structure structure. The 12” x 12” GLO imaging plates outperform scintillator glass for MeV radiography, due to higher light yield (55,000 Ph/MeV) and better stopping, while providing spatial resolution of >8 lp/mm for MeV X-rays.

Transparent polycrystalline ceramic scintillators based on the garnet structure and incorporating gadolinium for high stopping power are being developed for use in gamma spectrometers. Optimization of energy resolution for gamma spectroscopy involves refining the material composition for high stopping and high light yield, developing ceramics fabrication methodology for material homogeneity, as well as selecting the size and geometry of the scintillator to match the photodetector characteristics and readout electronics. We have demonstrated energy resolution of 4% at 662 keV for 0.05 cm3 GYGAG(Ce) ceramics with photodiode readout, and 4.9% resolution at 662 keV for 18 cm 3 GYGAG(Ce) ceramics and PMT readout. Comparative gamma spectra acquired with GYGAG(Ce) and NaI(Tl) depict the higher resolution of GYGAG(Ce) for radioisotope identification applications. Light yield non-proportionality of garnets fabricated following different methods reveal that the fundamental shapes of the light yield dependence on energy are not intrinsic to the crystal structure, but may instead depend on trap state distributions. With exposure to 9 MeV Brehmsstrahlung radiation, we also find that GYGAG(Ce) ceramics exhibit excellent radiation hardness.

Purpose: In medical imaging, data scaling is sometimes desired to handle the system complexity, such as uniformity calibration. Since the data are usually saved in short integer, conventional data scaling will first scale the data in floating point format and then truncate or round the floating point data to short integer data. For example, when using truncation, scaling of 9 by 1.1 results in 9 and scaling of 10 by 1.1 results in 11. When the count level is low, such scaling may change the local data distribution and affect the intended application of the data. Methods: In this work, the authors use an example gated cardiac SPECT study to illustrate the effect of conventional scaling by factors of 1.1 and 1.2. The authors then scaled the data with the same scaling factors using a randomization approach, in which a random number evenly distributed between 0 and 1 is generated to determine how the floating point data will be saved as short integer data. If the random number is between 0 and 0.9, then 9.9 will be saved as 10, otherwise 9. In other words, the floating point value 9.9 will be saved in short integer value as 10 with 90% probability or 9 with 10% probability. For statistical analysis of the performance, the authors applied the conventional approach with rounding and the randomization approach to 50 consecutive gated studies from a clinical site. Results: For the example study, the imagereconstructed from the original data showed an apparent perfusion defect at the apex of the myocardium. The defect size was noticeably changed by scaling with 1.1 and 1.2 using the conventional approaches with truncation and rounding. Using the randomization approach, in contrast, the images from the scaled data appeared identical to the original image. Line profile analysis of the scaled data showed that the randomization approach introduced the least change to the data as compared to the conventional approaches. For the 50 gated data sets, significantly more studies showed quantitative differences between the original images and the images from the data scaled by 1.2 using the rounding approach than the randomization approach [46/50 (92%) versus 3/50 (6%), p 0.05 ]. Likewise, significantly more studies showed visually noticeable differences between the original images and the images from the data scaled by 1.2 using the rounding approach than randomization [29/50 (58%) versus 1/50 (2%), p 0.05 ]. Conclusions: In conclusion, the proposed randomization approach minimizes the scaling-introduced local data change as compared to the conventional approaches. It is preferred for nuclear medicine data scaling.

Background In cardiac SPECT perfusion imaging, motion correction of the data is critical to the minimization of motion introduced artifacts in the reconstructed images. Software-based (data-driven) motion correction techniques are the most convenient and economical approaches to fulfill this purpose. However, the accuracy is significantly affected by how the data complexities, such as activity overlap, non-uniform tissue attenuation, and noise are handled. Methods We developed STASYS, a new, fully automatic technique, for motion detection and correction in cardiac SPECT. We evaluated the performance of STASYS by comparing its effectiveness of motion correcting patient studies with the current industry standard software (Cedars-Sinai MoCo) through blind readings by two readers independently. Results For 204 patient studies from multiple clinical sites, the first reader identified (1) 69 studies with medium to large axial motion, of which STASYS perfectly or significantly corrected 86.9% and MoCo 72.5%; and (2) 20 studies with medium to large lateral motion, of which STASYS perfectly or significantly corrected 80.0% and MoCo 60.0%. The second reader identified (1) 84 studies with medium to large axial motion, of which STASYS perfectly or significantly corrected 82.2% and MoCo 76.2%; and (2) 34 studies with medium to large lateral motion, of which STASYS perfectly or significantly corrected 58.9% and MoCo 50.0%. Conclusions We developed a fully automatic software-based motion correction technique, STASYS, for cardiac SPECT. Clinical studies showed that STASYS was effective and corrected a larger percent of cardiac SPECT studies than the current industrial standard software.

We report on the development of two new mechanically rugged, high light yield transparent ceramic scintillators: (1) Ce-doped Gd-garnet for gamma spectroscopy, and (2) Eu-doped Gd-Lu-bixbyite for radiography. GYGAG(Ce) garnet transparent ceramics offer ρ = 5.8g/cm3, Zeff = 48, principal decay of 8 lp/mm.

Breakthrough energy resolution, R(662keV) < 4%, has been achieved with an oxide scintillator, Cerium-doped Gadolinium Yttrium Gallium Aluminum Garnet, or GYGAG(Ce). Transparent ceramic GYGAG(Ce), has a peak emission wavelength of 550 nm that is better matched to Silicon photodetectors than to standard PMTs. We are therefore developing a spectrometer based on pixelated GYGAG(Ce) on a Silicon photodiode array that can provide R(662 keV) = 3.6%. In comparison, with large 1-2 in3 size GYGAG(Ce) ceramics we obtain R(662 keV) = 4.6% with PMT readout. We find that ceramic GYGAG(Ce) of a given stoichiometric chemical composition can exhibit very different scintillation properties, depending on sintering conditions and post-anneal treatments. Among the characteristics of transparent ceramic garnet scintillators that can be controlled by fabrication conditions are: scintillation decay components and their amplitudes, intensity and duration of afterglow, thermoluminescence glow curve peak positions and amplitudes, integrated light yield, light yield non-proportionality - as measured in the Scintillator Light Yield Non-Proportionality Characterization Instrument (SLYNCI), and energy resolution for gamma spectroscopy. Garnet samples exhibiting a significant fraction of Cerium dopant in the tetravalent valence also exhibit: faster overall scintillation decay, very low afterglow, high light yield, but poor light yield proportionality and degraded energy resolution.

Disclosed technology can provide a process for generating reconstructed muon image resolution to optimize the use of the limited angular range muon track data collected by a muon tomography system. In one aspect, a process for improving reconstructed muon image resolution for a volume of interest (VOI) imaged by a muon tomography system includes: collecting raw muon track data of cosmic ray muon tracks passing through the VOI; grouping the raw muon track data into two or more subsets of tracks based on at least one angular distribution of the muon tracks in the raw muon track data; generating a set of images of the VOI based on the two or more subsets of tracks; and combining information from the set of reconstructed images and a reconstructed image based on the full set of the raw muon track data to obtain a resulting reconstructed image of the VOI.

Muon tomography uses naturally occurring cosmic rays to detect nuclear threats in containers. Currently there are no systematic image characterization metrics for muon tomography. We propose a set of image characterization methods to quantify the imaging performance of muon tomography. These methods include tests of spatial resolution, uniformity, contrast, signal to noise ratio (SNR) and vertical smearing. Simulated phantom data and analysis methods were developed to evaluate metric applicability. Spatial resolution was determined as the FWHM of the point spread functions in X, Y and Z axis for 2.5cm tungsten cubes. Uniformity was measured by drawing a volume of interest (VOI) within a large water phantom and defined as the standard deviation of voxel values divided by the mean voxel value. Contrast was defined as the peak signals of a set of tungsten cubes divided by the mean voxel value of the water background. SNR was defined as the peak signals of cubes divided by the standard deviation (noise) of the water background. Vertical smearing, i.e. vertical thickness blurring along the zenith axis for a set of 2 cm thick tungsten plates, was defined as the FWHM of vertical spread function for the plate. These image metrics provided a useful tool to quantify the basic imaging properties for muon tomography.

Bad pixel correction on pixelated solid-state detectors typically uses the average of the direct neighboring pixels (AVG) to derive the value of a bad pixel. However, the AVG approach was suboptimal for high resolution imaging. Therefore, we developed a least gradient approach (LGA) in this work. In the LGA approach, the gradients of the image in a 5 × 5 box centered at the bad pixel were calculated along the two orthogonal and two diagonal directions. The value of the bad pixel was derived from the average of the two neighboring pixels along the direction in which the gradient was the least. For 18 cardiac SPECT studies, we added to the data randomly generated bad pixels and bad pixels in a specially designed pattern and then corrected the bad pixels using the AVG approach. Images reconstructed from the bad-pixel-free data and the bad-pixel-corrected data were compared. For high resolution imaging, we used line and bar phantom studies to evaluate the AVG and LGA approaches on a pixelated solid-state gamma camera. Patient studies showed no visible qualitative or significant quantitative difference between the images reconstructed from the bad-pixel-free and bad-pixel-corrected data. The maximum segment change ranged from 0% to 7.4% with average of 3.6 for data with randomly generated bad pixels. Blind reading of the images by an expert nuclear cardiologist showed no diagnostic difference for any of the patients. The line phantom studies showed two bad pixels not corrected by the AVG approach but corrected by the LGA approach. Bar phantom studies showed ten bad pixels not corrected by the AVG approach. But 9 out the 10 bad pixels were corrected using the LGA approach. The commonly used averaging approach (AVG) was effective for cardiac SPECT imaging but the least gradient approach (LGA) developed in this work was more effective for high resolution imaging.

Respiratory motion gating (R-Gating) in SPECT myocardial perfusion imaging (MPI) usually requires external devices and extra work of the technologist for patient setup. In this paper, we developed an operator-passive R-Gating technique without external devices. Method: Using the thoracic impedance approach, the respiratory motion signal was obtained simultaneously with the ECG signal from the same ECG leads. With list-mode acquisition, the respiratory motion signal was tagged to the SPECT data and was used to rebin the list-mode data into R-Gating data. Forty consecutive patients were scanned to evaluate and establish the R-Gating approach. Both the conventional data and the list-mode data were saved. Then forty eight consecutive patients were scanned for respiratory motion assessment using the established approach. Results: The summed R-Gating images were different from the summed ECG-gating images in only three of the forty patients (7.5%) and equivalent in the rest of the patients (92.5%). R-Gating with six respiratory phases showed optimal motion detection and image quality compromise. The R-Gating images illustrated different types of motion of the heart during respiratory cycles, including 3-D translation, apparent rotation of the heart along the long axis, and pivoting at the base. The observed motion of the heart in R-Gating images correlated well with the detected respiratory motion signal. For the motion assessment studies, 28/48 (58.3%) showed no motion or small motion, 20/48 (41.7%) of stress and 18/48 (37.3%) of rest studies showed medium motion, and 2/48 (4.2%) of rest studies showed large motion. In conclusion, we developed an effective operator-passive approach for respiratory motion gating for SPECT MPI.

Background: Thallium doped CsI(Tl) scintillators read out with PIN photodiodes have been successfully used for high performance pixilated solid-state gamma cameras for cardiac SPECT and general nuclear systems. These cameras allow for both emission and transmission scans because of their good energy resolution and count-rate performance. We have reported previously on the performance of detector modules employing small CsI(Tl) scintillators (2.8×2.8×6mm) where the dominant limiting factor for both energy resolution and count-rate performance is CsI(Tl) itself. Methods: We compared identical shaped CsI(Tl) and newly introduced Ce-doped (Gd,Y) 3 (Al, Ga) 5 O 12 (GYGAG) transparent ceramics (with fast decay time), read out with our PIN photodiode based detector modules, characterizing the light yield, energy resolution and count-rate performance obtainable with GYGAG at 140keV. Results: We measured luminosities of 42,000 and 64,000 Ph./MeV for GYGAG and CsI(Tl) respectively. GYGAG had a decay time that allowed use of a 6µs shaping time instead of the 12µs required for optimal energy resolution with CsI(Tl), enabling >2x improvement in count-rate performance. Though GYGAG was more proportional than CsI(Tl), the energy resolution was not improved over CsI(Tl) at 140keV due to its lower luminosity. However, we measured energy resolution of 4.0% at 662keV for GYGAG on our 3mm photodiode detector modules, better than the 5.3% estimated for CsI(Tl). After exposure to ambient light, GYGAG's residual fluorescence was ∼800 times that from CsI(Tl) and had 3 decay components. The longest component contributed at 6% of the total, and had a decay time troublesome for PMT measurements, though it did not significantly affect the energy resolution measured with photodiodes.

We have developed a CsI(Tl)/PIN detector module for high resolution SPECT and low dose photon-counting CT imaging. Using the detector modules with 6.1mm pixels, we built a cardiac SPECT system with three detector heads. The detector heads form a triple-head (each 20×15cm), geometry for emission scans and reconfigure to form a large transaxial field-of-view (FOV) geometry for transmission scans using an x-ray based transmission source. Anthropomorphic phantom and patient data was used to evaluate the performance of the new cardiac SPECT camera. We then developed modules with 2.8mm pixel size to further improve the spatial resolution, improving energy resolution to 7.5%. Improved energy resolution was achieved by improving the crystal arrays, electronics and packaging of the module. Using the 2.8mm modules, we built a large FOV planar imager (39×31cm), and evaluated its emission performance with clinical studies and its CT performance with an anthropomorphic phantom. The count rate capability was 20kcps per detector pixel. The combined SPECT/CT scan was completed in 5 min, resulting in high quality and accuracy attenuation maps (μ H20 @140keV was 0.151+/−0.003/cm at ∼5μSv CT dose). The large FOV imager showed excellent clarity and high resolution for emission bone studies and demonstrated reconstructed CT image quality suitable for attenuation correction or image fusion and localization (∼150μSv CT dose).

In medical imaging, data scaling is sometimes desired to handle the system complexity, such as uniformity calibration. Since the data are usually saved in short integer, conventional data scaling will first scale the data in floating point format and then truncate or round the floating point data to short integer data. For example, when using truncation, scaling of 9 by 1.1 results in 9 and scaling of 10 by 1.1 results in 11. When the count level is low, such scaling may change the local data distribution and affect the intended application of the data.In this work, the authors use an example gated cardiac SPECT study to illustrate the effect of conventional scaling by factors of 1.1 and 1.2. The authors then scaled the data with the same scaling factors using a randomization approach, in which a random number evenly distributed between 0 and 1 is generated to determine how the floating point data will be saved as short integer data. If the random number is between 0 and 0.9, then 9.9 will be saved as 10, otherwise 9. In other words, the floating point value 9.9 will be saved in short integer value as 10 with 90% probability or 9 with 10% probability. For statistical analysis of the performance, the authors applied the conventional approach with rounding and the randomization approach to 50 consecutive gated studies from a clinical site.For the example study, the image reconstructed from the original data showed an apparent perfusion defect at the apex of the myocardium. The defect size was noticeably changed by scaling with 1.1 and 1.2 using the conventional approaches with truncation and rounding. Using the randomization approach, in contrast, the images from the scaled data appeared identical to the original image. Line profile analysis of the scaled data showed that the randomization approach introduced the least change to the data as compared to the conventional approaches. For the 50 gated data sets, significantly more studies showed quantitative differences between the original images and the images from the data scaled by 1.2 using the rounding approach than the randomization approach [46/50 (92%) versus 3/50 (6%), p0.05]. Likewise, significantly more studies showed visually noticeable differences between the original images and the images from the data scaled by 1.2 using the rounding approach than randomization [29/50 (58%) versus 1/50 (2%), p0.05].In conclusion, the proposed randomization approach minimizes the scaling-introduced local data change as compared to the conventional approaches. It is preferred for nuclear medicine data scaling.

Background We developed a cardiac SPECT system (X-ACT) with low dose volume CT transmission-based attenuation correction (AC). Three solid-state detectors are configured to form a triple-head system for emission scans and reconfigured to form a 69-cm field-of-view detector arc for transmission scans. A near mono-energetic transmission line source is produced from the collimated fluorescence x-ray emitted from a lead target when the target is illuminated by a narrow polychromatic x-ray beam from an x-ray tube. Transmission scans can be completed in 1 min with insignificant patient dose (deep dose equivalent

We developed a new cardiac SPECT system (X-ACT) with a low dose volume CT transmission-based attenuation correction (AC). Three solid-state detectors are configured to form a triple-head system for emission scans and reconfigured to form a large 27” (69 cm) field-of-view (FOV) detector arc for transmission scans. The transmission line source is the collimated fluorescence X-ray emitted from a lead target when the lead target is fluxed by a narrow X-ray beam from an X-ray tube. High quality transmission scans can be completed in as short as one minute with insignificant patient dose (~5 μSv). For evaluation, we scanned an anthropomorphic phantom with a uniform cardiac insert and the same anthropomorphic phantom with one 60o full defect and one 45o 50% defect in the cardiac insert. We also scanned an ACR phantom and a uniform cylindrical phantom. Results showed that image uniformity and defect contrast were improved by AC in the anthropomorphic phantom studies as compared to without AC (NAC). The inferior to anterior wall ratio and the septal to lateral wall ratio were 0.99 and 1.16 before and 1.02 and 1.00 after AC. The defect contrast of the full and 50% defect was 0.528 and 0.156 before and 0.628 and 0.173 after AC. The ACR phantom images with AC showed correction of the bowing effect due to attenuation in the NAC images. The reconstructed attenuation coefficient of water at 140 keV was 0.154±0.003/cm and 0.157±0.002/cm in the liver and cardiac regions of the anthropomorphic phantom, and 0.150±0.003/cm in the uniform region of the ACR phantom and the uniform cylindrical phantom. In conclusion, the X-ACT system generated accurate attenuation maps with one-minute transmission scans. Phantom studies showed that AC improved image quality and quantification over NAC.