CZT System Research Articles

Bias and precision of SPECT-based 177Lu activity-concentration estimation using a ring-configured solid-state versus a dual-headed anger system

BackgroundThe aim was to compare bias and precision for 177Lu-SPECT activity-concentration estimation using a dual-headed Anger SPECT system and a ring-configured CZT SPECT system. This was investigated for imaging at 208 keV and 113 keV, respectively.MethodsPhantom experiments were performed on a GE Discovery 670 system with 5/8’’ NaI(Tl) crystal (dual-headed Anger system) and a GE StarGuide (ring-configured CZT system). Six spheres (1.2 mL to 113 mL) in a NEMA PET body phantom were filled with 99mTc and 177Lu, separately. Mean relative errors and coefficients of variation (CV) in estimated sphere activity concentration were studied over six timeframes of 10 min each for the two systems. For 177Lu, similar acquisitions were also performed for an anthropomorphic phantom with two spheres (10 mL and 25 mL) in a liver with non-radioactive background and a sphere-to-background ratio of 15:1. Tomographic reconstruction was performed using OS-EM with 10 subsets with compensation for attenuation, scatter, and distance-dependent spatial resolution. For the Anger system, up to 40 iterations were used and for the ring-configured CZT system up to 30 iterations were used.ResultsThe two systems showed similar mean relative errors and CVs for 177Lu when using an energy window around 208 keV, while the ring-configured system demonstrated a lower bias for a similar CV compared to the Anger system for 99mTc and for 177Lu when using an energy window around 113 keV. However, total activity in the phantom tended to be overestimated in both systems for these cases.ConclusionsThe ring-configured CZT system is a viable alternative to the dual-headed Anger system equipped with medium-energy collimators for 177Lu-SPECT and shows a potential advantage for activity-concentration estimation when operated at 113 keV. However, further consideration of the preservation of total activity is warranted.

Accurate and efficient rapid acquisition early post-injection stress-first CZT SPECT myocardial perfusion imaging with tetrofosmin and attenuation correction.

Myocardial perfusion imaging (MPI) protocols have not changed significantly despite advances in instrumentation and software. We compared an early post-injection, stress-first SPECT protocol to standard delayed imaging. 95 patients referred for SPECT MPI were imaged upright and supine on a Spectrum Dynamics D-SPECT CZT system with CT attenuation correction. Patients received injection of 99mTc tetrofosmin at peak of regadenoson stress and were imaged. Early post-stress (mean 17 ± 2 minutes) and Standard 1-h delay (mean 61 ± 13 min). Three blinded readers evaluated images for overall interpretation, perceived need for rest imaging, image quality, and reader confidence. Laboratory efficiency was also evaluated. Blinded readers had the same response for the need for rest in 77.9% of studies. Studies also had the same interpretation in 89.5% of studies. Reader confidence was high (86.0% (Early) and 90.3% (Standard p=0.52. Image quality was good or excellent in 87.4% Early vs 96.8% Standard (p=0.09). Time between patient check-in and end of stress imaging was 104 ± (Standard) to 60 ± 18 minutes (Early) (p<0.001). Early post-injection stress-only imaging using CZT SPECT/CT appears promising with Tc-99m tetrofosmin with similar image quality, reader confidence, diagnosis, and need for a rest scan.

3D-Ring CZT System With New Low- and Medium-Energy Range: Ultrafast Dual-Isotope Lung SPECT/CT Improvement.

New 3D-ring CZT systems with low- and medium-energy-range detectors allow for simultaneous dual-isotope lung scintigraphy. We compared 10-, 7-, 5-, and 3-minute acquisitions for 99mTc and 81mKr performed simultaneously on StarGuide CZT-SPECT/CT and reframed in 50 patients. Ventilation/perfusion mismatches were calculated (mean, 15.6% ± 28%), and Spearman correlation coefficients of mismatches were 0.994, 0.994, and 0.984 between 10- and 7-, 5-, and 3-minute acquisitions, respectively. No visual difference in image quality or final diagnosis was found. 3D-ring CZT-SPECT with low and medium energy range detectors allows ultrafast dual-isotope lung scintigraphy up to 3 minutes.

Detection of prostate cancer bone metastases with fast whole-body 99mTc-HMDP SPECT/CT using a general-purpose CZT system

BackgroundWe evaluated the effects of acquisition time, energy window width, and matrix size on the image quality, quantitation, and diagnostic performance of whole-body 99mTc-HMDP SPECT/CT in the primary metastasis staging of prostate cancer.MethodsThirty prostate cancer patients underwent 99mTc-HMDP SPECT/CT from the top of the head to the mid-thigh using a Discovery NM/CT 670 CZT system with list-mode acquisition, 50-min acquisition time, 15% energy window width, and 128 × 128 matrix size. The acquired list-mode data were resampled to produce data sets with shorter acquisition times of 41, 38, 32, 26, 20, and 16 min, narrower energy windows of 10, 8, 6, and 4%, and a larger matrix size of 256 × 256. Images were qualitatively evaluated by three experienced nuclear medicine physicians and quantitatively evaluated by noise, lesion contrast and SUV measurements. Diagnostic performance was evaluated from the readings of two experienced nuclear medicine physicians in terms of patient-, region-, and lesion-level sensitivity and specificity.ResultsThe originally acquired images had the best qualitative image quality and lowest noise. However, the acquisition time could be reduced to 38 min, the energy window narrowed to 8%, and the matrix size increased to 256 × 256 with still acceptable qualitative image quality. Lesion contrast and SUVs were not affected by changes in acquisition parameters. Acquisition time reduction had no effect on the diagnostic performance, as sensitivity, specificity, accuracy, and area under the receiver-operating characteristic curve were not significantly different between the 50-min and reduced acquisition time images. The average patient-level sensitivities of the two readers were 88, 92, 100, and 96% for the 50-, 32-, 26-, and 16-min images, respectively, and the corresponding specificities were 78, 84, 84, and 78%. The average region-level sensitivities of the two readers were 55, 58, 59, and 56% for the 50-, 32-, 26-, and 16-min images, respectively, and the corresponding specificities were 95, 98, 96, and 95%. The number of equivocal lesions tended to increase as the acquisition time decreased.ConclusionWhole-body 99mTc-HMDP SPECT/CT can be acquired using a general-purpose CZT system in less than 20 min without any loss in diagnostic performance in metastasis staging of high-risk prostate cancer patients.

Gated Tomographic Radionuclide Angiography Using 3D-Ring CZT StarGuide SPECT/CT Head-To-Head Comparison With a Cardiac-Dedicated CZT Camera

Gated tomographic radionuclide angiography can assess and monitor left cardiac function. Dedicated cardiac CZT cameras have enabled dose reduction and quicker acquisitions. New 3D-ring CZT general purpose systems are now available. We report 50 patients who underwent a 7-minute acquisition on a cardiac-dedicated CZT camera and 9 minutes on a new 3D-ring CZT system after mean injection of 321.4 ± 55.9 MBq 99mTc-labelled human serum albumin. There was no significant difference in left ventricular volumes, and left and right ventricular ejection fractions. These preliminary results seem to validate the use of 3D-ring CZT system for LEVF and cardiac function evaluation.

Technical note: 3D‐printed phantom for dedicated cardiac protocols and geometries in nuclear medicine

The purpose of this study was to create and validate a 3D-printed nuclear cardiac phantom for low cost, user-friendly design and easy implementation with modern cardiac SPECT systems. This new phantom design aims to address common problems with commercial phantoms such as lengthy setup, prohibitive cost, and overly large size, while improving the overall functionality of the phantom. The phantom was developed using computer aided design software and fabricated with a 3D printer using optimized watertight printing protocols. The phantom design includes six low perfusion lesions within a stylized myocardium of the left ventricle that are placed in the common quantitation sectors for polar maps. The validation of this phantom was completed with two dedicated cardiac SPECT systems; a dual head gamma camera and a multi-pinhole CZT system. Multiple SPECT acquisitions were used to demonstrate the functionality of the phantom. Polar maps were reconstructed and used to score the contrast detectability based on the number of visible low contrast objects representing "lesions." The images reconstructed from the various acquisitions on both SPECT systems closely resemble a clinical examination. Lesion visibility followed the expected relationships between protocol changes affecting contrast and spatial resolution. Lesion visibility improved with iterative reconstruction against filtered back projection. A phantom of a stylized left ventricle with fillable myocardium was developed, 3D printed, and implemented for cardiac nuclear medicine. The phantom simulates the task of perfusion imaging and successfully demonstrates differences in image quality depending on imaging protocol. This study validates the 3D-printed design as a low cost and user-friendly phantom that can be easily scanned and scored using various systems, in particular those implementing a nontraditional cardio-centric geometry.

Evaluation of a new multipurpose whole-body CzT-based camera: comparison with a dual-head Anger camera and first clinical images

BackgroundEvaluate the physical performance of the VERITON CzT camera (Spectrum Dynamics, Caesarea, Israel) that benefits from new detection architecture enabling whole-body imaging compared to that of a conventional dual-head Anger camera.MethodsDifferent line sources and phantom measurements were performed on each system to evaluate spatial resolution, sensitivity, energy resolution and image quality with acquisition and reconstruction parameters similar to those used in clinical routine. Extrinsic resolution was assessed using 99mTc capillary sources placed successively in air, in a head and in a body phantom filled with background activity. Spectral acquisitions for various radioelements used in nuclear medicine (99mTc, 123I, 201Tl, 111In) were performed to evaluate energy resolution by computing the FWHM of the measured photoelectric peak. Tomographic sensitivity was calculated by recording the total number of counts detected during tomographic acquisition for a set of source geometries representative of different clinical situations. Sensitivity was also evaluated in focus mode for the CzT camera, which consisted of forcing detectors to collect data in a reduced field-of-view. Image quality was assessed with a Jaszczak phantom filled with 350 MBq of 99mTc and scanned on each system with 30-,20-,10- and 5-min acquisition times.ResultsExtrinsic and tomographic resolution in the brain and body phantoms at the centre of the FOV was estimated at 3.55, 7.72 and 6.66 mm for the CzT system and 2.47, 7.75 and 7.72 mm for the conventional system, respectively. The energy resolution measured at 140 keV was 5.46% versus 9.21% for the Anger camera and was higher in a same manner for all energy peaks tested. Tomographic sensitivity for a point source in air was estimated at 236 counts·s−1·MBq−1 and increased to 1159 counts·s−1·MBq−1 using focus mode, which was 1.6 times and 8 times greater than the sensitivity measured on the scintillation camera (144 counts·s−1·MBq−1). Head and body measurements also showed higher sensitivity for the CzT camera in particular with focus mode. The Jaszczak phantom showed high image contrast uniformity and a high signal-to-noise ratio on the CzT system, even when decreasing acquisition time by 6-fold. Representative clinical cases are shown to illustrate these results.ConclusionThe CzT camera has a superior sensitivity, higher energy resolution and better image contrast than the conventional SPECT camera, whereas spatial resolution remains similar. Introduction of this new technology may change current practices in nuclear medicine such as decreasing acquisition time and activity injected to patient.

Effect of CZT system characteristics on Compton scatter event recovery.

Improving 511 keV photon detection sensitivity is a common goal for positron emission tomography system designers. One attractive approach to increase sensitivity is recovering events that are normally rejected. The kinematics of Compton scattering can be used to recover the line of response through direction difference angle (DDA). The uncertainty of DDA is determined by the energy and spatial resolution of a system. In this work, we evaluated the performance of small animal CZT-based positron emission tomography systems with energy resolution of 1%, 4%, and 6% and different spatial resolution based on prior work for guiding new design efforts. Designs with energy resolution limited by counting statistics and by electronic noise were considered. The influence of modifying the conventional energy window and uncertainty of DDA was investigated. For a system with 4% energy resolution and limited by electronic noise, the figure of merit of noise equivalent count increases by 65% as the lower energy bound increases from 471 keV to 493 keV. If the system-wide energy resolution becomes worse than 4% of the full width half maximum at 511 keV, going to a pixel size finer than 1 mm has very limited effect in reducing total angular uncertainty. For a system with 1% energy resolution, as the spatial resolution improves from 1 mm to 0.5 mm, the contrast-to-noise ratio increases by 9%.

Measuring the mutual effects between a CZT detector and MRI for the development of a simultaneous MBI/MRI insert.

While mammography is the gold standard for breast cancer screening, it suffers from poor sensitivity in women with dense breast tissue. Both breast MRI and molecular breast imaging (MBI) have been used as secondary imaging techniques. However, breast MRI suffers from low specificity and low sensitivity in MBI. A CZT based detector system has been developed with the goal of simultaneous MBI/MRI imaging to address the shortcomings of each modality. The performance of each modality needs to be addressed separately and together. The CZT system is comprised of four Redlen CZT modules tiled in a 2x2 array. Each module consists of 256 pixels and feature a builtin on-board ASIC and FPGA. A custom digital readout circuit board was designed to interface the four modules with a microcontroller to a PC. MR images were acquired with a 3T GE Discovery MR750 and Hologic breast coils. A gradient echo imaging sequence was used for all image acquisitions. A tissue mimicking phantom with a plastic grid insert (1 cm spacing) was used to evaluate geometric accuracy with the CZT detectors in the MRI bore. The average distance between the grid markers was 1A}0.2cm indicating negligible geometric distortion. Field maps were generated with a uniform phantom to quantify the effect on magnetic field homogeneity. Early results indicate a significant distortion (~10ppm) in the magnetic field closest to the coil. Further analysis of the MR images will determine the extent of image quality degradation. A flood map of Tc-99m was acquired to evaluate and implement an energy correction map and a uniformity map. In the absence of a magnetic field, the mean energy resolution at 140keV was 6.3%. After fully characterizing the uniformity, geometric accuracy and sensitivity, the same metrics will be evaluated in the MRI bore.

Optimization of ultra-soft CoZrTa/SiO2/CoZrTa trilayer elements for integrated inductor structures

We show the optimization of magnetic properties of ferromagnetic (FM)/SiO2/FM trilayer structures as potential candidates for the magnetic core in toroidal integrated inductors, with FM materials Co91.5Zr4.0Ta4.5 (CZT) and Ni80Fe20 (Py). In the single-layer parent films, we found a monotonic reduction of easy-axis coercivity (Hc down to 0.17 Oe in CZT, 0.4 Oe in Py) with increasing dc magnetron sputtering voltage. In the trilayer rectangular structures, with induced easy-axis in the short lateral dimension, we found proof of dipolar coupling between the two FM layers from BH loop measurements in the CZT system, showing linear response with minimal hysteresis loss when the external field is applied in the long axis. Py elements did not show this optimized property. Further investigation of domain configurations using scanning transmission x-ray microscopy suggests an insufficient induced anisotropy in Py compared with the shape anisotropy to realize the antiparallel-coupled state.

High‐Energy Density Dielectrics and Capacitors for Elevated Temperatures: Ca(Zr,Ti)O3

The Ca(Zr1−xTix)O3 (CZT) solid solution system is a linear dielectric that is of interest for high‐temperature power capacitor applications. This dielectric was synthesized by conventional solid‐state processes and prototyped into single‐layer CZT capacitors, which were fabricated with interdigitated electrodes cofired between dielectric layers ~10‐μm thick. The dielectric properties of these capacitors were extensively investigated as a function of Zr/Ti ratio on the CaZrO3 side of the solid solution. The electrostatic energy density and breakdown strength of the CZT capacitors were investigated by measuring polarization–electric field curves as a function of temperature from room temperature to 250°C. The Ca(Zr0.80Ti0.20)O3 capacitors show high electrostatic energy density of 4 J/cm3 at 250°C. Highly accelerated life testing (HALT) was also performed on these dielectrics, and we quantified the thermal stimulated depolarization current (TSDC) to access the major point defects in the CZT system.

TU‐G‐110‐03: Optimal Techniques for Dual Energy and Spectral Breast Computed Tomography with an Iodinated Contrast Agent

Purpose: To investigate the optimal techniques for dual energy and spectral breast computed tomography with an iodinated contrast agent.Methods: Simulations were performed for three CT systems. The first system was based on a CsI flat panel detector and used a dual kVp technique. The second and third systems were based on a CZT photon counting detector with energy resolution and single kVp technique. The first CZT system used a single threshold to separate photons from one acquisition into either low or high energy images. The second CZT system used multiple thresholds to separate photons from one acquisition into one of five energy images. Iodine images for the dual kVp system and the two energy CZT system were generated under the assumption that a linear three material decomposition contains glandular tissue, adipose tissue and iodine. For the second CZT system, iodine images were generated using an iterative likelihood maximization algorithm. Beam energies ranging from 40 to 140 kVp were simulated for all systems. A figure‐of‐merit (FOM), defined as the dual energy signal‐to‐noise ratio of contrast in the iodine image divided by the square root of mean glandular dose, was used to quantify imaging performance. Results: The highest FOM, normalized to 1.0, was seen with the two energy CZT system at a beam energy of 40 kVp. Performance from the five energy CZT system was highest at 46 kVp with an FOM value of 0.75. The FOM of the dual kVp was maximized at beam energies of 48 kVp and 140 kVp with a value of 0.28. Conclusion: The results of this study indicate that a CZT based CT system of either configuration could potentially produce images of significantly higher quality than that of a comparable flat panel based dual energy CT system.

The X-ray imager on AXO

DSRI has initiated a development program of CZT X-ray and gamma-ray detectors employing strip readout techniques. A dramatic improvement of the energy response was found operating the detectors as the so-called drift detectors. For the electronic readout, modern ASIC chips were investigated. Modular design and the low-power electronics will make large area detectors using the drift strip method feasible. The performance of a prototype CZT system will be presented and discussed. One such detector system has been proposed for future space missions: the X-Ray Imager (XRI) on the Atmospheric X-ray Observatory (AXO), which is a mission proposed to the Danish Small Satellite Program and is dedicated to observations of X-ray generating processes in the Earth's atmosphere. Of special interest will be simultaneous optical and X-ray observations of sprites that are flashes appearing directly above an active thunderstorm system. Additional objective is a detailed mapping of the auroral X-ray and optical emission. XRI comprises a coded mask and a 20×40 cm 2 CZT detector array covering an energy range from 5 to 200 keV.