Cadmium Zinc Telluride Detectors Research Articles

Unsupervised Learning for Improved Gamma-Ray Spectrometry in Pixelated Cadmium Zinc Telluride (CZT) Detectors

Machine learning has been found to be ubiquitously useful across many industries, presenting an opportunity to improve radiation detection performance using data-driven algorithms. Improved detector resolution can aid in the detection, identification, and quantification of radionuclides. In this work, a novel, data-driven, unsupervised learning approach is developed to improve detector spectral characteristics by learning, and subsequently rejecting, poorly performing regions of the pixelated detector. Feature engineering is used to fit individual characteristic photo peaks to a Doniach lineshape with a linear background model. Then, principal component analysis is used to learn a lower-dimension latent space representation of each photo peak where the pixels are clustered, and subsequently ranked, based on the cluster mean distance to an optimal point. Pixels within the worst cluster(s) are rejected to improve the full-width at half-maximum (FWHM) by 10% to 15% (relative to the bulk detector) at 50% net efficiency when applied to training data obtained from measurements of a 100 μCi 154Eu source using a H3D M400i pixelated cadmium zinc telluride detector. These results compare well with, but do not outperform, a greedy algorithm that accumulates pixels in order of FWHM from lowest to highest used as a benchmark. In the future, this approach can be extended to include the detector energy and angular response. Finally, the model is applied to newly seen natural and enriched uranium spectra relevant for nuclear safeguards applications.

Assessing Tissue Differentiation Capabilities in X-ray Imaging Through Cadmium Zinc Telluride (CZT) Photon Counting Detectors.

In recent years, the use of photon-counting detection technology has resulted in significant X-ray imaging research. This advanced technology holds considerable promise for enhancing Computed Tomography (CT) scanners, offering a potential solution to the limitations inherent in traditional CT detectors. The ongoing studies are dedicated to assessing the effectiveness and sensitivity of semiconductor detector materials in photon counting detectors, particularly in their ability to detect soft tissue contrasts. This study aimed to characterize the performance of the Cadmium Zinc Telluride (CZT) photon counting detector in identifying various tissues with a focus on assessing its sensitivity in distinguishing tissue types in X-ray imaging. An optimal frame rate per second (FPS) of the CZT detector was evaluated by setting the X-ray tube voltage and current at 25 keV and 35 keV and 0.5 mA, 1.0 mA respectively. By keeping the optimum FPS fixed, the detector energy thresholds were set in small steps from 15 keV to 35 keV and the tube currents were set for X-ray tubes in ranges of 0.1 mA to 1.0 mA to evaluate the relationship between voltage and current of the X-ray source and counts per second (CPS). The specimens, including fat, liver, muscles, paraffin wax, and contrast media were placed on a stair-step chamber constructed from Plexi-glass, spanning six distinct thickness levels. We investigated X-ray transmission across these tissue samples at varying thicknesses, exploring five energy thresholds: 21 keV, 25 keV, 29 keV, 31 keV, and 45 keV to evaluate their impact on the CPS. This study found that a frame rate of 12 frames per second optimally aligns with the spectral response of the X-ray source. Furthermore, a linear correlation is present between the CPS and the X-ray tube current. The transmission of X-rays through a sample depends on its thickness, a phenomenon observed across different energy thresholds in this study. The detectors exhibit high sensitivity and linearity, ensuring accurate and reliable measurements in diverse imaging scenarios, making them invaluable tools for precise data acquisition in both research and clinical applications.

Uranium measurements in the field using high-resolution cadmium zinc telluride detectors

A new generation of cadmium zinc telluride (CZT) detectors has become available and is being evaluated by the International Atomic Energy Agency (IAEA) for safeguards verifications in the field. The new CZT detector, model M400, is a room temperature spectrometer manufactured by H3D, Inc. The M400 demonstrates superior energy resolution, effective isotope identification capabilities, and convenient usability features when tested in a controlled laboratory environment. These characteristics define the M400 as a potential platform for IAEA field detection applications, which could become suitable for nuclear material characterization (e.g., enrichment verification) and nuclear safeguards missions. The capabilities of gamma spectrometry codes including Fixed energy, Response function Analysis with Multiple efficiencies (FRAM) from Los Alamos National Laboratory, CZT for Uranium (CZTU) from Lawrence Livermore National Laboratory, and Gamma Detector Response and Analysis Software (GADRAS) from Sandia National Laboratories were adapted for M400 spectra, and the performance of the codes has been validated. This was reported in a prior work. To further validate the performance of the high-energy resolution CZT detector and the isotopic analysis codes, a field measurement campaign consisting of uranium hexafluoride (UF6) cylinder measurements was conducted at a fuel fabrication facility. A total of 34 Type 30B cylinders containing UF6 were measured using three different M400 CZT detectors. Each detector was outfitted with a custom rectangular collimator and shield made out T-Flex®, a tungsten-impregnated polymer. Measurements were performed at three different locations of the cylinder, ensuring that the measurement geometry satisfied the infinite thickness criterion. The spectra from the M400 CZT were analyzed using the code General Enrichment Meter (GEM). For analyzing the gamma-ray spectra from UF6 cylinder, the GEM code is the appropriate tool since it relies only on the gamma-ray emissions from 235U and not from other isotopes. Results from the spectral analysis were compared with the known abundance of 235U in the cylinders, as well as with the International Target Values 2020 (ITV2020). The suitability of the different underlying techniques used by the various codes for UF6 analysis is discussed. The challenges of measuring UF6 contained in cylinders and mitigation strategies are highlighted.

INVESTIGATION OF CENTERING PROBLEM IN THE CADMIUM ZINC TELLURIDE (CZT) CARDIAC CAMERA

Introduction: Cadmium Zinc Telluride (CZT) Cardiac Cameras are a special SPECT cameras with solid state cadmium zinc telluride detectors. This diagnostic method applied in the evaluation of coronary artery disease is well designed for myocardial perfusion scintigraphy. Aim: CZT cardiac cameras have limited detector area. In patients who are morbidly obese or whose heart is not in its normal location in the body, the center of the heart and the isocenter of the device do not coincide. It is aim to investigate how these conditions affect the imaging performance of the CZT cardiac camera. Methods: A homogeneous and spherical ball with a diameter of 4 cm was used for the research. To be able to measure away from the center a wooden phantom with 8 cavities and a total length of 32 cm was designed. The center as reference point has been determined by matching the center of the device with the center of the sphere. For the next imaging, the image were taken by placing the spherical ball in the other cavities, respectively, without changing the center. Results: According to the results obtained, farther from the center, deviations from sphericity and differences in dose distribution were observed. Counts decreased by 1.5% in the 2nd position and 16% in the 3rd position relative to the center in the X-axis. A disaster area has been formed and the image area has been exited from the 4th imaging. Conclusion: It is very important to center the patient as much as possible, otherwise the doctor will misdiagnose.

Impact of Flexible Circuit Bonding and System Integration on Energy Resolution of Cross-Strip CZT Detectors.

Cadmium zinc telluride (CZT) detectors enable high spatial resolution and high detection efficiency and are utilized for many gamma-ray and X-ray spectroscopy applications. In this article, we describe a stable bonding process and report on the characterization of cross-strip CZT detectors before and after bonding to flexible circuit. The bonding process utilizes gold stud bonding and polymer epoxy technique to bond the flexible circuits to two CZT crystals and form a detector module in an anode-cathode-cathode-anode (ACCA) configuration. The readout electronics is optimized in terms of shaper setting and steering electrode voltage. The average full-width half maximum (FWHM) energy resolution at 662 keV of 110 CZT crystals tested individually was 3.5% ± 0.59% and 4.75% ± 0.48% prebonded and post-bonded, respectively. No depth correction was performed in this study. The average FWHM energy resolution at 662 keV of the scaled-up system with 80 CZT crystals was 4.40% ± 0.53%, indicating the scaled-up readout electronics and stacking of the modules does not deteriorate performance. The proper shielding and grounding of the scaled-up system slightly improved the system-wide performance. The FWHM energy resolution at 511 keV of the scaled-up system was 5.85% ± 0.73%.

Development of a Compton camera based on 3D position-sensitive virtual Frisch-grid CZT detectors

In this study, a Compton camera was developed utilizing a 2 × 2 array of cadmium–zinc–telluride (CZT) detectors. The camera employs four CZTs, each measuring 6 mm × 6 mm × 19 mm. The virtual Frisch-grid method with a four-segment side pad was applied to ensure accurate 3D position sensing. In addition, rejection and correction methods were developed that leverage positional information to correct for non-uniform detector responses. Various isotopes were measured to evaluate the spectral performance. The energy resolutions were 3.11, 2.36, 2.00, 1.65, 1.31, and 1.50% at 356, 511, 662, 1275, and 1332 keV, respectively. In addition, to estimate depth, a comparison was made between the performance of cathode signal-based and side electrode-based methods, and their interchangeability was confirmed. Additionally, Compton imaging experiments were performed for single and multiple sources at various positions, and an iterative method was implemented for image reconstruction. Although the imaging performance varied depending on the gamma-ray direction, our system was able to accurately reconstruct the positions of single or multiple sources. The intrinsic efficiency, spatial resolution, and positional error were determined to be (1.43 ± 0.36) × 10−3, 16.42° ±7.02°, and 3.43° ±1.62°, respectively.

Identification of shielded sources using a CZT detector and an unmanned ground vehicle

This work is dedicated to ability of a coplanar cadmium zinc telluride (CZT) detector to identify lost/orphan radioactive sources hidden inside soil layers. Considering point-like sources placed in soil and the CZT detector fixed on an unmanned ground vehicle (UGV), relevant measurement geometries were proposed. Full-energy peak efficiency (FEPE) calibrations of the CZT detector were prepared using the MCNP6.1 radiation transport code. In order to check the simulation set-up, control measurements were performed and compared with the Monte Carlo simulations.FEPEs obtained were used for estimations of minimum detectable activities (MDA) and their dependencies on the source depth in soil. Thereafter, field tests of the CZT detector were performed. Within field measurements, radioactive sources with known activities slightly above the MDA values were placed in upper layers of soil of a grassed meadow. The meadow surface was scanned by the CZT detector mounted on a mobile ground robotic platform remotely controlled by an operator. Results of the radiation mapping with the CZT detector were depicted as maps of count rates. On the basis of the maps created, positions of shielded sources were clearly revealed.

Same same but different: dopamine transporter SPECT on scanners with CZT vs. NaI detectors

BackgroundThe aims of this study were to establish a normal database (NDB) for semiquantification of dopamine transporter (DAT) single-photon emission computed tomography (SPECT) with [123I]FP-CIT on a cadmium zinc telluride (CZT) camera, test the preexisting NaI-derived NDB for use in CZT scans, and compare the diagnostic findings in subjects imaged with a CZT scanner with either the preexisting NaI-based NDB or our newly defined CZT NDB.MethodsThe sample comprised 73 subjects with clinically uncertain parkinsonian syndrome (PS) who prospectively underwent [123I]FP-CIT SPECT on a CZT camera according to standard guidelines with identical acquisition and reconstruction protocols (DaTQUANT). Two experienced readers visually assessed the images and binarized the subjects into “non-neurodegenerative PS” and “neurodegenerative PS”. Twenty-five subjects from the “non-neurodegenerative PS” subgroup were randomly selected to establish a CZT NDB. The remaining 48 subjects were defined as “test group”. DaTQUANT was used to determine the specific binding ratio (SBR). For the test group, SBR values were transformed to z-scores for the putamen utilizing both the CZT NDB and the manufacturer-provided NaI-based NDB (GE NDB). A predefined fixed cut-off of -2 was used for dichotomization of z-scores to classify neurodegenerative and non-neurodegenerative PS. Performance of semiquantification using the two NDB to identify subjects with neurodegenerative PS was assessed in comparison with the visual rating. Furthermore, a randomized head-to-head comparison of both detector systems was performed semiquantitatively in a subset of 32 out of all 73 subjects.ResultsCompared to the visual rating as reference, semiquantification based on the dedicated CZT NDB led to fewer discordant ratings than the GE NDB in CZT scans (3 vs. 8 out of 48 subjects). This can be attributed to the putaminal z-scores being consistently higher with the GE NDB on a CZT camera (median absolute difference of 1.68), suggesting an optimal cut-off of -0.5 for the GE NDB instead of -2.0. Average binding ratios and z-scores were significantly lower in CZT compared to NaI data.ConclusionsUse of a dedicated, CZT-derived NDB is recommended in [123I]FP-CIT SPECT with a CZT camera since it improves agreement between semiquantification and visual assessment.

A preliminary study of dobutamine myocardial flow reserve on 99mTc-Sestamibi CZT-SPECT

With improved resolution and sensitivity, the cadmium zinc telluride (CZT) detector measures myocardial blood flow (MBF) and myocardial flow reserve (MFR) via single photon emission computed tomography (SPECT). Recently, many studies have used vasodilator stress to obtain quantitative indexes. However, dobutamine used as a pharmaceutical stress has been rarely used to quantify myocardial perfusion using CZT-SPECT. Our study retrospectively analyzed the blood flow performance of 99mTc-Sestamibi (99mTc -MIBI) CZT-SPECT comparing dobutamine to adenosine. The study aims to explore whether dobutamine stress can be used for the myocardial perfusion quantitative analysis via CZT-SPECT as well as compare dobutamine MBF and MFR to adenosine. It was a retrospective study. A total of 68 patients with suspected or known coronary artery disease (CAD) were consecutively enrolled in this study. Thirty-four patients underwent dobutamine stress 99mTc-MIBI CZT-SPECT. Another thirty-four patients underwent adenosine stress 99mTc-MIBI CZT-SPECT. Patient characteristics, myocardial perfusion imaging (MPI) results, gated-myocardial perfusion imaging (G-MPI) results and quantitative analysis of MBF and MFR were collected. In dobutamine stress group, stress MBF was significantly higher than rest MBF (median [interquartile range], 1.63 [1.46-1.94] vs. 0.89 [0.73-1.06], P < 0.001). In adenosine stress group, similar results were observed (median [interquartile range], 2.01 [1.34-2.20] vs. 0.88 [0.75-1.01], P < 0.001). When comparing the dobutamine and adenosine stress group, global MFR showed significant differences (median [interquartile range], the dobutamine group: 1.88 [1.67-2.38] vs. the adenosine group: 2.19 [1.87-2.64], P = 0.037). MBF and MFR can be measured using dobutamine 99mTc -MIBI CZT-SPECT. In small sample single-center study, there was a difference in MFR produced by adenosine and dobutamine within the suspected or the known CAD population.

The potential of dynamic 99mTc-sestamibi cadmium zinc telluride-single-photon emission computed tomography camera assessing myocardial flow reserve in patients with heart failure with preserved ejection fraction.

Coronary microvascular dysfunction (CMD) is related to the pathophysiology, mortality, and morbidity of heart failure with preserved ejection fraction (HFpEF). A novel single-photon emission computed tomography (SPECT) camera with cadmium zinc telluride (CZT) detectors allows for the quantification of absolute myocardial blood flow and myocardial flow reserve (MFR) in patients with coronary artery disease. However, the potential of CZT-SPECT assessing for CMD has never been evaluated in patients with HFpEF. The clinical records of 127 consecutive patients who underwent dynamic CZT-SPECT were retrospectively reviewed. Rest and stress scanning were started simultaneously with 3 and 9 MBq/kg of 99mTc-sestamibi administration, respectively. Dynamic CZT-SPECT imaging data were analysed using a net-retention model with commercially available software. Transthoracic echocardiography was performed in all patients. The MFR value was significantly lower in the HFpEF group (mean ± SEM = 2.00 ± 0.097) than that in the non-HFpEF group (mean ± SEM = 2.74 ± 0.14, P = 0.0004). A receiver operating characteristic analysis indicated that if a cut-off value of 2.525 was applied, MFR could efficiently distinguish HFpEF from non-HFpEF. Heart failure with preserved ejection fraction had a consistently low MFR, regardless of the diastolic dysfunction score. Heart failure with preserved ejection fraction patients with MFR values lower than 2.075 had a significantly higher incidence of heart failure exacerbation. Myocardial flow reserve assessed by CZT-SPECT was significantly reduced in patients with HFpEF. A lower MFR was associated with a higher hospitalization rate in these patients. Myocardial flow reserve assessed by CZT-SPECT has the potential to predict future adverse events and stratify the severity of disease in patients with HFpEF.

Design of a Low-Dose, Stationary, Tomographic Molecular Breast Imaging System Using 3-D Position Sensitive CZT Detectors

Molecular breast imaging (MBI) has been shown to have high sensitivity for lesion detection, particularly in patients with dense breasts where conventional mammography is limited. However, relatively high radiation dose and long imaging time are limiting factors. Most current MBI systems are based on planar imaging. Improved performance can be achieved using tomographic techniques, which normally involve detector motion. Our goal is to develop a low-dose stationary tomographic MBI system with similar or better performance in terms of lesion detection compared to planar MBI. The proposed system utilizes two opposing cadmium zinc telluride detectors with high intrinsic resolution and depth of interaction (DOI) capability, combined with densely packed multipinhole collimators. This leads to improved efficiency and adequate angular sampling, but also to significant multiplexing (MX), which can result in artefacts. We have developed de-MX algorithms that take advantage of the DOI information. We have performed both analytic and Monte Carlo simulations to demonstrate the feasibility, optimize the design and investigate the expected performance of the proposed system. Lesion detectability was preserved with reduction of acquisition time (or radiation dose) by a factor of 2 compared to planar images at the lowest reported dose. The first prototype is under evaluation at Kromek.

Advances in High-Energy-Resolution CdZnTe Linear Array Pixel Detectors with Fast and Low Noise Readout Electronics.

Radiation detectors based on Cadmium Zinc Telluride (CZT) compounds are becoming popular solutions thanks to their high detection efficiency, room temperature operation, and to their reliability in compact detection systems for medical, astrophysical, or industrial applications. However, despite a huge effort to improve the technological process, CZT detectors' full potential has not been completely exploited when both high spatial and energy resolution are required by the application, especially at low energies (<10 keV), limiting their application in energy-resolved photon counting (ERPC) systems. This gap can also be attributed to the lack of dedicated front-end electronics which can bring out the best in terms of detector spectroscopic performances. In this work, we present the latest results achieved in terms of energy resolution using SIRIO, a fast low-noise charge sensitive amplifier, and a linear-array pixel detector, based on boron oxide encapsulated vertical Bridgman-grown B-VB CZT crystals. The detector features a 0.25-mm pitch, a 1-mm thickness and is operated at a -700-V bias voltage. An equivalent noise charge of 39.2 el. r.m.s. (corresponding to 412 eV FWHM) was measured on the test pulser at 32 ns peaking time, leading to a raw resolution of 1.3% (782 eV FWHM) on the 59 keV line at room temperature (+20 °C) using an uncollimated 241Am, largely improving the current state of the art for CZT-based detection systems at such short peaking times, and achieving an optimum resolution of 0.97% (576 eV FWHM) at 1 µs peaking time. The measured energy resolution at the 122 keV line and with 1 µs peaking time of a 57Co raw uncollimated spectrum is 0.96% (1.17 keV). These activities are in the framework of an Italian collaboration on the development of energy-resolved X-ray scanners for material recycling, medical applications, and non-destructive testing in the food industry.

Positional correction of a 3D position-sensitive virtual Frisch-grid CZT detector for gamma spectroscopy and imaging based on a theoretical assumption

The virtual Frisch-grid method for room-temperature radiation detectors has been widely used because of its simplicity and high performance. Recently, side electrodes were separately attached to each surface of the detectors instead of covering the entire detector surface with a single electrode. The side-electrode structure enables the measurement of the three-dimensional (3D) gamma-ray interaction in the detector. The positional information of the interaction can then be utilized to precisely calibrate the response of the detector for gamma-ray spectroscopy and imaging. In this study, we developed a 3D position-sensitive 5 × 5 × 12 mm3 cadmium-zinc-telluride (CZT) detector and applied a flattening method to correct detector responses. Collimated gamma-rays incident on the surface of the detector were scanned to evaluate the positional accuracy of the detection system. Positional distributions of the radiation interactions with the detector were imaged for quantitative and qualitative evaluation. The energy spectra of various radioisotopes were measured and improved by the detector response calibration according to the calculated positional information. The energy spectra ranged from 59.5 keV (emitted by 241Am) to 1332 keV (emitted by 60Co). The best energy resolution was 1.06% at 662 keV when the CZT detector was voxelized to 20 × 20 × 10.

Experimental Evaluation of a 3-D CZT Imaging Spectrometer for Potential Use in Compton-Enhanced PET Imaging.

We constructed a prototype positron emission tomography (PET) system and experimentally evaluated large-volume 3-D cadmium zinc telluride (CZT) detectors for potential use in Compton-enhanced PET imaging. The CZT spectrometer offers sub-0.5-mm spatial resolution, an ultrahigh energy resolution (~1% @ 511 keV), and the capability of detecting multiple gamma-ray interactions that simultaneously occurred. The system consists of four CZT detector panels with a detection area of around 4.4 cm × 4.4 cm. The distance between the front surfaces of the two opposite CZT detector panels is ~80 mm. This system allows us to detect coincident annihilation photons and Compton interactions inside the detectors and then, exploit Compton kinematics to predict the first Compton interaction site and reject chance coincidences. We have developed a numerical integration technique to model the near-field Compton response that incorporates Doppler broadening, detector's finite resolutions, and the distance between the first and second interactions. This method was used to effectively reject random and scattered coincidence events. In the preliminary imaging studies, we have used point sources, line sources, a custom-designed resolution phantom, and a commercial image quality (IQ) phantom to demonstrate an imaging resolution of approximately 0.75 mm in PET images, and Compton-based enhancement.

Properties of Redlen cadmium zinc telluride with respect to x-ray spectroscopy

We present a study of a sample pixelated cadmium zinc telluride (CZT) detector using CZT purchased from Redlen Technologies. We demonstrate that the material shows good uniformity across the 2 cm × 2 cm × 3 mm crystal in terms of leakage current, gain, and spectral resolution. We find that the detector produces very good spectral resolution for energies up to at least 105 keV, achieving a full-width at half-maxima of 450 eV at 14 keV up to 880 eV at 105 keV using only single-pixel events. Though our analysis of spectra including multiple-pixel events is somewhat limited, we also produce a spectrum including events in which photon energy is deposited across two adjacent pixels. We find that this degrades the energy resolution by up to 30%, but this result can likely be improved using more rigorous calibrations. Additionally, we investigate depth-of-interaction effects, showing that spectral resolution can be improved by 3% to 7% for energies between 86 and 105 keV by removing events beyond a certain depth. Performing this cut reduces efficiency, removing 13% to 21% of photons from the resulting spectral lines.

A peak shape function building and comparison of cadmium zinc telluride detector for gamma-ray spectrum

A peak shape function building and comparison of cadmium zinc telluride detector for gamma-ray spectrum

Sub-voxel identification of gamma-ray interaction positions within a pixelated CZT detector through signal analysis

Cadmium zinc telluride (CZT) detectors are well suited for use in gamma-imaging applications thanks to their room-temperature operation, excellent energy resolution, and three-dimensional sensitivity to positions of gamma-ray interactions. In many of these applications, the position resolution with which gamma-interactions can be determined is crucial for high quality imaging. Finer pixelisation may provide improved position resolution but at the cost of increased fabrication cost and degradation of spectral performance. This work sets out to instead investigate and quantify the three-dimensional position resolution achievable using pulse shape analysis applied to digital signals, arising from interactions in a CZT detector pixelated into 2 × 2 × 5 mm3 voxels. The signal response of a 3 × 3 pixel cluster has been characterised as a function of gamma-ray interaction position using collimated 57Co and 137Cs sources. Simple pulse shape analysis algorithms using the transient image and charge collection signals have been developed and applied to achieve a sub-voxel position resolution of better than 0.65 × 0.69 × 1.26 mm3 at 122 keV and of 1.06 mm through 5 mm depth at 662 keV, not accounting for divergence of the collimated beam used to evaluate performance. Assessment of the contribution of the diverging gamma-beam placed a lower bound on the achievable positions resolution in 5 mm thickness at 122 keV of 290μm.

Monte-Carlo simulation for detecting neutron and gamma-ray simultaneously with CdZnTe half-covered by gadolinium film

Neutron is an indirectly ionizing particle without charge, which is normally measured by detecting reaction products. Neutron detection system based on measuring gadolinium-converted gamma-rays is a good way to monitor the neutron because the representative prompt gamma-rays of gadolinium have low energies (79, 89, 182, and 199 keV). Low energy gamma-rays and their high attenuation coefficient on materials allow the simple design of a detector easier to manufacture. Thus, we designed a cadmium zinc telluride detector to investigate feasibility of simultaneous detection of gamma-rays and neutrons by using the Monte-Carlo simulation, which was divided into two parts; first was gamma-detection part and second was gamma- and neutron-simultaneous detection part. Consequently, we confirmed that simultaneous detection of gamma-rays and neutrons could be feasible and valid, although further research is needed for adoption on real detection.

Compton and proximity imaging of 225Ac in vivo with a CZT gamma camera: a proof of principle with simulations.

In vivo imaging of 225Ac is a major challenge in the development of targeted alpha therapy radiopharmaceuticals due to the extremely low injected doses. In this paper, we present the design of a multi-modality gamma camera that integrates both proximity and Compton imaging in order to achieve the demanding sensitivities required to image 225Ac with good image quality. We consider a dual-head camera, each of the heads consisting of two planar cadmium zinc telluride detectors acting as scatterer and absorber for Compton imaging, and with the scatterer practically in contact with the subject to allow for proximity imaging. We optimize the detector's design and characterize the detector's performance using Monte Carlo simulations. We show that Compton imaging can resolve features of up to 1.5 mm for hot rod phantoms with an activity of 1 μCi, and can reconstruct 3D images of a mouse injected with 0.5 μCi after a 15 minutes exposure and with a single bed position, for both 221Fr and 213Bi. Proximity imaging is able to resolve two 1 mm-radius sources of less than 0.1 μCi separated by 1 cm and at 1 mm from the detector, as well as it can provide planar images of 221Fr and 213Bi biodistributions of the mouse phantom in 5 minutes.

Predicted performance of a tangential viewing hard x-ray camera for the DIII-D high field side lower hybrid current drive experiment.

High field side launch of lower hybrid current drive (LHCD) has improved accessibility and penetration over low field side launch on DIII-D. Simulations predict single pass absorption under a wide range of plasma conditions. Hard x-ray (HXR) measurement of LHCD generated fast electron bremsstrahlung (50-250keV) will validate wave propagation and absorption. Emissivity profiles are recovered from one-dimensional inversion of HXR brightness to determine LH damping location, fast electron slowing down time, and some indication of the fast electron energy. The camera will be implemented by populating 32 tangential sightlines of the existing Gamma Ray Imager with Kromek SPEARTM Cadmium Zinc Telluride (CZT) detectors sensitive to 10-1000keV photons with 10keV energy resolution. Expected count rates allow for <0.5ms time resolution. Pulses are processed using 50ns shaping time Cremat CR-200 Gaussian shaping modules and are digitized by 25MHz D-TACQ ACQ216 digitizers. The performance of the HXR camera is evaluated by comparing predicted fast electron density profiles and inverted synthetic brightnesses obtained from the ray-tracing/Fokker-Planck codes GENRAY/CQL3D. Inversions closely matched predicted fast electron profiles for a range of experimental parameters.