Conventional NaI Research Articles

CdTe XG-Cam: A new high-resolution x-ray and gamma-ray camera for studies of the pharmacokinetics of radiopharmaceuticals in small animals.

The recent emergence of targeted radionuclide therapy has increased the demand for imagers capable of visualizing pharmacokinetics in developing radiopharmaceuticals in the preclinical phase. Some radionuclides emit hard x-rays and gamma-rays below 100 keV, in which energy range the performance of conventional NaI scintillators is poor. Multipinhole collimators are also used for small animal imaging with a good spatial resolution but have a limited field of view (FOV). In this study, a new imager with high sensitivity over a wide FOV in the low-energy band ( 100 keV) was developed for the pharmacokineticstudy. We developed an x-ray and gamma-ray camera for high-resolution spectroscopy, named "CdTe XG-Cam," equipped with a cadmium telluride semiconductor detector and a parallel-hole collimator using a metal 3D printer. To evaluate the camera-system performance, phantom measurements with single and dual nuclides ( , , and were performed. The performance for in vivo imaging was evaluated using tumor-bearing mice to which a nuclide ( or administered. We simultaneously obtained information on and , which emit emission lines in the low-energy band with peak energies close to each other (23-26 keV for and 27-31 keV for , and applied an analytical method based on spectral model fitting to determine the individual radioactivities accurately. In the small animal imaging, the distributions of the nuclide in tumors were accurately quantified and time-activity curves in tumors areobtained. The demonstrated capability of our system to perform in vivo imaging suggests that the camera can be used for applications of pharmacokineticsresearch.

Influence of short-lived radioiodines other than 131I on screening direct thyroid measurements with TCS-172 NAI(TL) survey meters.

In a nuclear emergency, one of the actions taken for the sake of public is to monitor thyroid exposure to radioiodines. Japan's Nuclear Regulation Authority recently published a report on such monitoring and proposed direct thyroid measurements with conventional NaI(Tl) survey meters (e.g. Hitachi model TCS-172) as a primary screening method. A previous study proposed screening levels (SLs) used in these simplified measurements as the net reading values of the TCS-172 device. Age-specific SLs were derived from a thyroid equivalent dose of 100mSv due to the inhalation intake of 131I. This study addressed the possible influence of short-lived iodine isotopes other than 131I on the simplified measurements. In preparation for such measurements, the responses of the device for 132I as an ingrowth component from 132Te, 133I, 134I and 135I in the thyroid were evaluated by numerical simulations using age-specific stylized phantoms in addition to those obtained for 131I in the previous study. The radioactivity ratios of the relevant isotopes were taken from the inventory data of the Fukushima Daiichi Nuclear Power Plant. The results were used to predict the net readings of the device when 132Te-132I and 133I as well as 131I were inhaled at 24 or 72h after the shutdown of a nuclear power plant. In these cases, the signals from 132Te-132I and 133I become undetectable a couple of days after intake, which could lead to underestimations of the thyroid dose. To estimate the thyroid dose accurately from the simplified measurements, it is necessary to identify the exact time of intake after the shutdown and the actual physiochemical property of 132Te that affects the thyroid uptake of 132I.

Screening levels of TCS-172 NaI(Tl) survey meters used for direct thyroid measurements in nuclear disasters.

It is a challenging task to establish a feasible and robust method for the population monitoring of individuals' thyroid exposure following an accidental intake of radioiodines in a nuclear emergency, because of the time restriction. The authors previously proposed a method for such monitoring to obtain as many reliable human data as possible and one of the components is simplified measurements by conventional NaI(Tl) survey meters that are intended to be used for the initial triage to identify significantly exposed individuals and get an overall picture of the exposure levels in a target population in a timely manner. This study determined screening levels (SLs) for a conventional NaI(Tl) survey meter (model TCS-172, Hitachi, Japan) using the conversion factor (131I kBq in the thyroid per μSv h-1) that were obtained from experiments and simulations with age-specific phantoms. The results demonstrated that the derived SLs for 100mSv thyroid equivalent dose were as follows: 0.2μSvh-1 (SL1) for the age group≤5-y-olds, 0.5μSvh-1 (SL2) for the 10- and 15-y-old age groups and 1.0μSvh-1 (SL3) for adults. These SLs would be reasonably available within 1week after the intake of 131I on the safe side.

Uncertainties associated with direct thyroid measurements using an NaI(Tl) survey meter: the effect of anatomical differences among individuals.

Photon detectors utilised for direct thyroid measurements to determine the radioiodine content in the thyroid are normally calibrated using a phantom that mimics the human neck, including the thyroid. However, such measurements are necessarily subject to uncertainty because of the difference between the phantom and the real human subject and also the morphological differences among individuals. In this study, personal voxel phantoms were created from magnetic resonance images of the necks of 24 adult volunteers (15 males and 9 females), and numerical simulations using these phantoms were performed to examine the variation in a conversion factor (131I kBq in the thyroid per μSvh-1) for a conventional NaI(Tl) survey meter among the individuals and also to confirm the suitability of reference Japanese voxel phantoms as a calibration standard for such measurements. As a result, it was found that the conversion factor obtained from the reference Japanese male (female) phantom was 1.29 (1.18) times larger than the average conversion factor for the male (female) subjects, suggesting that the conversion factors of the reference Japanese adult male and female phantoms would generally overestimate the 131I thyroidal contents and that the thyroid volume would be one of the factors influencing the conversion factor. This study also revealed a wide difference in the thyroid volume among individuals, which would be of concern when performing specific dose assessments for heavily exposed persons.

Effective population monitoring for determination of the thyroidal radioiodine content of the public following a nuclear accident in Japan

After a nuclear accident, population monitoring is necessary to determine the radiation exposure levels of the affected population. One of the monitoring components is direct thyroid measurements to assess the internal thyroid dose (mainly from 131I with a relatively short physical half-life: 8.02 days). These measurements are particularly important for young children but were not adequately performed after the 2011 Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Herein we propose a feasible and robust method to obtain as much reliable human data as possible for the dose reconstructions following a nuclear accident. The method employs three types of measurements: simplified, additional, and detailed measurements. The simplified measurements are performed using conventional NaI(Tl) survey meters to quickly triage heavily exposed individuals. The additional measurements are conducted using mobile whole-body counters to detect cesium (Cs; with longer retention in the body) as a tracer of 131I. And the detailed measurements are taken using spectrometric devices; they provide the most reliable data and are used to confirm the other measurements. We also discussed the target subjects and the monitoring period based on the experiences gained following the FDNPP accident. The early post-nuclear-accident phase is the most important period for the dose reconstruction for the affected populations; however, it is also the most challenging period in terms of allocating the necessary monitoring resources. It is thus vital that all countries that operate nuclear power plants establish and maintain a system for nuclear emergency preparedness and response.

CZT camera systems may provide better risk stratification for low-risk patients

BackgroundThe photon sensitivity and spatial resolution of single-photon emission-computed tomography (SPECT) has been significantly improved by solid-state camera systems using cadmium zinc telluride (CZT) detectors. While the diagnostic accuracy of these systems is well established, there is little evidence directly comparing the prognostic utility to conventional NaI cameras. Methods and ResultsRetrospective analysis of patients undergoing SPECT between 2008 and 2012. Visual SPECT assessment was performed utilizing the 17-segment model to determine summed stress scores (SSS). We identified 12,830 consecutive patients, mean age 63.2 ± 13.7 and 56.1% male, 5072 of whom underwent CZT and 7758 NaI imaging. During a median follow-up duration of 7.0 years (IQR 5.5-8.2), a total of 2788 (21.7%) patients died. Compared to SSS 0, minimal perfusion abnormality (SSS 1-3) was associated with increased all-cause mortality with CZT camera (adjusted HR 1.32, P = .017) and NaI camera (adjusted HR 1.29, P = .001, interaction P = .803). Increasing stress abnormality was associated with a similar increase in risk with CZT or NaI imaging (interaction P > .500). In a propensity matched analysis, patients with normal perfusion stress perfusion assessed with a CZT was associated with decreased mortality compared to normal perfusion assessed by a NaI camera system (hazard ratio .88, 95% CI .78-.99, P = .040). ConclusionsIncreasing stress perfusion abnormality was associated with similar increase in all-cause mortality with CZT or NaI cameras. CZT and NaI camera systems provide similar risk stratification, however, normal myocardial perfusion may be associated with a more benign prognosis when assessed with a CZT camera system.

Development of a new hand-held type thyroid monitor using multiple GAGG detectors for young children following a nuclear accident

One of the most important lessons learned from the Fukushima Daiichi Nuclear Power Plant accident is that direct (in vivo) measurements of thyroid exposure to radioiodine (mainly, 131I) in the affected populations should be initiated in a timely manner. Furthermore, the existing commercial detectors are not necessarily suitable for the measurement of young children, who are especially vulnerable to radiation exposure and therefore important to screen. This paper presents the development of a new thyroid monitor for such measurements and the results from phantom-based experiments. The monitor has two unique probes having multiple high-energy-resolution type Gd3(Al,Ga)5O12(Ce) (GAGG) detectors that can be placed directly on the young subject's anterior neck. The crystal size of the GAGG detector is 1 cm3, and a probe consisting of a 4 × 1 or 4 × 2 detector array can be selected depending on the subject's body size. The thickness of the 4 × 1 array probe is 24 mm, which is less than that for a conventional NaI(Tl) survey meter having a crystal 1 inch in diameter and 1 inch long (38 mm). Experimental and computational calibrations of the new monitor using existing and virtual phantoms allowed us to determine the full energy peak efficiency for the 131I thyroid contents of different age groups from 3-mo-old to 10-yr-old and minimum detectable activity (MDA) values under various conditions. As a result, the attainable MDA for subjects age ≤5 years under a normal background level (∼0.05 μSv h−1) was found to be ∼30 Bq, which was low enough to identify children with thyroid-equivalent doses over 10 mSv up to about 25 days after the 131I intake. Our new monitor would be useful in direct thyroid measurements for vulnerable young children following a large nuclear accident.

Evaluation of a variable-aperture full-ring SPECT system using large-area pixelated CZT modules: A simulation study for brain SPECT applications.

Single photon emission computed tomography (SPECT) scanners using cadmium zinc telluride (CZT) offer compact, lightweight, and improved imaging capability over conventional NaI(Tl)-based SPECT scanners. The main purpose in this study is to propose a full-ring SPECT system design with eight large-area CZT detectors that can be used for a broad spectrum of SPECT radiopharmaceuticals and demonstrate the performance of our system in comparison to the reference conventional NaI(Tl)-based two-head Anger cameras. A newly designed full-ring SPECT system is composed of eight large-area CZT cameras (128mm×179.2mm effective area) that can be independently swiveled around their own axes of rotation independently and can have radial motion for varying aperture sizes that can be adapted to different sizes of imaging volume. Extended projection data were generated by conjoining projections of two adjacent detectors to overcome the limited field-of-view (FOV) by each CZT camera. Using Monte Carlo simulations, we evaluated this new system design with digital phantoms including a Derenzo hot rod phantom and a Zubal brain phantom. Comparison of performance metrics such as spatial resolution, sensitivity, contrast-to-noise ratio (CNR), and contrast-recovery ratio was made between our design and conventional SPECT scanners having different pixel sizes and radii of rotation (one clinically well-known type and two arbitrary types matched to our proposed CZT-SPECT geometries). The proposed scanner could result in up to about three times faster in acquisition time over conventional scan time at same acquisition time per step. The spatial resolution improvement, or deterioration, of our proposed scanner compared to the clinical-type scanner was dependent upon the location of the point source. However, there were overall performance improvements over the three different setups of the conventional scanner particularly in volume sensitivity (approximately up to 1.7 times). Overall, we successfully reconstructed the phantom image for both 99m Tc-based perfusion and 123 I-based dopamine transporter (DaT) brain studies simulated for our new design. In particular, the striatal/background contrast-recovery ratio in 3-to-1 reference ratio was over 0.8 for the 123 I-based DaT study. We proposed a variable-aperture full-ring SPECT system using combined pixelated CZT and energy-optimized parallel-hole collimator modules and evaluated the performance of this scanner using relevant digital phantoms and MC simulations. Our studies demonstrated the potential of our new full-ring CZT-SPECT design, showing reduced acquisition time and improved sensitivity with acceptable CNR and spatial resolution.

Energy Resolution of Scintillators in Connection With Track Structure

The large spread of scintillator performance (light yield and energy resolution) from a theoretical limit shows that we are still far from the deep understanding of the phenomena. Usually, extrinsic aspects of resolution degradation (such as purity, defects, stoichiometry, and so on) are the subject of study. At the same time, intrinsic factors (such as track structure, excitation density, and uniformity) that depend on crystal lattice can play a dominant role in scintillator performance. Some progress in the understanding of these problems is achieved by using the concept of different efficiencies of photon emission from excited regions with different concentrations of electronic excitations. The regions with a high or low concentration of thermalized excitations result in the nonradiative losses of excitations and, therefore, produce additional event-to-event fluctuations. The technique of multidimensional analysis of the time-resolved pulse shape is proposed for the clustering of all the events according to the proximity of the waveform to some centroids of the clusters. This procedure shows that even conventional NaI:Tl and CsI:Tl scintillators allow to achieve an energy resolution of about 3% for 662-keV gamma photons.

A new thyroid monitor using multiple high resolution Gd3(Al,Ga)5O12(Ce) detectors for direct thyroid measurements of small children following a nuclear accident

We developed a new thyroid monitor using multiple high energy resolution Gd3(Al,Ga)5O12(Ce) (HR-GAGG) detectors (each crystal size = 1-cm3), in particular with an intention of measuring small children (including infants) for their internal thyroid exposure from radioiodine following a nuclear accident. The small-sized HR-GAGG detectors allowed to be placed around the human neck at the close distance to increase the geometrical efficiency for 131I localized in the thyroid. We tested two arrangements of the eight HR-GAGG detectors using four age-specific phantoms in each of which a thyroid-shaped container filled with standard 131I solution was installed. The results demonstrated that the minimum detectable activity (MDA) of the new monitor reached 20–30 Bq with a counting time of 180 s, which is significantly lower than that of a conventional NaI(Tl) survey meter (crystal size: 1-inch-dia,1-inch-thick) commonly used for measuring air dose rates.

In vivo measurement of pre-operational spallation source workers: baseline body burden levels and detection limits of relevant gamma emitters using high-resolution gamma spectrometry

As a measure to prepare for long-term internal dose monitoring of workers at the European Spallation Source (ESS) in Lund, Sweden, operated by the European Research Infrastructure Consortium (ERIC), as well as to enhance emergency preparedness against accidental releases, a series of in vivo measurements were conducted using a high-resolution HPGe detector with a 123% relative efficiency (1.332 MeV). This study describes the whole-body counting set-up, calibration procedure, and subsequent validation measurements using conventional NaI(Tl)-scanning-bed geometry on a selection of workers from the ESS. Detection limits for the relevant gamma emitters 7Be, 172Hf, and 182Ta were determined to be 65 Bq, 130 Bq, and 22 Bq, respectively, using a 2400 s acquisition time. The baseline measurements suggest that care must be taken to ensure that the fluctuations in the presence of radon daughters 214Bi and 214Pb are minimised by, for example, ensuring a minimum air exchange between the measuring room and the ambient air, and by demanding that the measured subjects change clothes and shower before measurement. Furthermore, in a monitoring program for internal doses to spallation source workers, the presence of radionuclides originating from non-work-related sources (such as 226Ra from private water wells or 137Cs from intakes of Chernobyl contaminated foodstuffs), or radionuclides from previous work history (such as 60Co within the nuclear power industry), must be considered.

SIMULATION OF THE RESPONSE OF A LaBr3(Ce) DETECTOR IN AN ATMOSPHERE CONTAMINATED WITH RADIONUCLIDES AFTER A NUCLEAR POWER PLANT ACCIDENT.

The aim of this paper is to investigate the possibility of using detectors based on LaBr3(Ce) scintillation crystal as part of gamma spectrometry systems for field use and possibly as part of a monitoring network around nuclear power plants, i.e. whether LaBr3(Ce) detectors can follow the classical scintillation detectors based on NaI (Tl). For this purpose, the Monte Carlo simulation of the IPROL-1 probe response was performed in the simplified geometry of the radionuclides-contaminated atmosphere. A study shows that a LaBr3(Ce)-based probe is usable for this purpose and results are at least comparable to those with a conventional NaI (Tl)-based probe.

Conceptual design of a large pixelated CZT detector with four-hole collimator matched pixel detector for SPECT imaging: a Monte Carlo simulation study

Significant progress has been achieved in the design of pixelated CZT detectors dedicated to cardiac and breast SPECT imaging. However, their detector geometry and associated collimators' design have limited their clinical use. The aim of this work is to determine the best combination between a large pixelated CZT detector and parallel-hole collimator that can provide high spatial resolution at low injected activity with low-energy radiotracers. Our proposed combination resulted in the design of a novel four-hole matched pixel detector (4-HMPD) configuration. Our novel 4-HMPD design based on large pixelated CZT detector was firstly compared to the standard one-hole matched pixel detector (1-HMPD) configuration using Monte Carlo simulation. We have also predicted the influence of pixel size, interpixel gap and source-to-collimator distance on the basis of resulting spatial resolution, sensitivity and crosstalk events fraction for three collimator hole lengths for Tc-99m (140 keV) . Thereafter, we used the same detector and collimator settings of the 1-HMPD configuration as constructed with the D-SPECT camera module (Redlen Technologies, BC, Canada) for our 4-HMPD design to compare the performance of the two configurations. Our preliminary results showed that a large pixel size, a small interpixel gap and a small collimator hole length increased significantly the sensitivity at the detriment of spatial resolution. The performance comparison between the 4-HMPD and the 1-HMPD configurations demonstrated an improved reconstructed spatial resolution (by a factor two), higher contrast with the large sphere of the modified Jaszczak phantom (from 63.1% to 39.1%), clear appearance of cold spheres (>14 mm diameter) and the cold cylinders (> 11.1 mm diameter). The crosstalk events fraction varied from 8.5% to 12.8%. Our novel detector/collimator combination allows less electronic readout complexity, less crosstalk events between pixels and twofold increase in septal thickness resulting in low septal penetration compared to the classical 1-HMPD configuration. It also showed the highest enhancement in terms of spatial resolution even in cases of low sensitivity with less injected activity, and outperformed the performance of existing conventional NaI (TI) crystal-based systems.

Development of a flexible γ-ray detector using a liquid scintillation light guide (LSLG)

A flexible γ detector using a liquid scintillation light guide (LSLG) was developed. The analyzed pulse height (PHA) spectrum depended on the diameter, length and scintillator concentration of the LSLG, and the distance of a γ ray irradiation point from the head of photomultiplier tube (PMT). From the analysis of PHA spectrum, it was found that the count ratio of two divided channel regions linearly decreases as the distance from the PMT head increases. It was further found that the radiation dose rate can be estimated by setting the flexible LSLG tube to a circular shape since the count rate is proportional to the dose rate measured by a conventional NaI (Tl) scintillation detector. Therefore, a flexible and long LSLG detector using a single PMT is useful for determination of the dose rate and has a potential to detect local contaminations in a certain narrow space.

Results from the first cryogenic NaI detector for the COSINUS project

Recently there is a flourishing and notable interest in the crystalline scintillator material sodium iodide (NaI) as target for direct dark matter searches. This is mainly driven by the long-reigning contradicting situation in the dark matter sector: the positive evidence for the detection of a dark matter modulation signal claimed by the DAMA/LIBRA collaboration is (under so-called standard assumptions) inconsistent with the null-results reported by most of the other direct dark matter experiments. We present the results of a first prototype detector using a new experimental approach in comparison to conventional single-channel NaI scintillation light detectors: a NaI crystal operated as a scintillating calorimeter at milli-Kelvin temperatures simultaneously providing a phonon (heat) plus scintillation light signal and particle discrimination on an event-by-event basis. We evaluate energy resolution, energy threshold and further performance parameters of this prototype detector developed within the COSINUS R&D project.

BaWF8 Crystals – Efficient X-Ray Luminophores

The spectral-kinetic characteristics of cerium- and chromium-doped samples of BaWF8 synthesized by the hydrothermal method were investigated. A luminescence band peaking at 490 nm with half-width 150 nm was found. It is shown that in the terms of the conventional luminophore NaI(Tl) the integral light yield of the x-ray luminescence equals 32% for BaWF8 crystals and 36.5% for BaWF8:2%CrF3. No afterglow of the experimental crystals is observed 20 msec after irradiation stops. Analysis shows that undoped and doped BaWF8 crystals synthesized by the hydrothermal method are promising materials for x-ray tomography.

Quantitative Measurement of Dual-Radioisotopes of Technetium-99m and Iodine-123 in Blood Samples With a Cadmium-Telluride-Based Counting Device

Our previous study demonstrated that a cadmium telluride (CdTe)-based single-photon emission computed tomography (SPECT) system with good energy resolution could provide dual-radioisotope SPECT images of a patient who had been administered with two kinds of radioisotope simultaneously. To obtain two quantitative physiological parametric images from these radioisotope images by using compartment model analysis, the concentrations of the dual-radioisotope in the blood sample need to be measured. In this paper, a CdTe-based well counter was developed to measure the concentrations of a dual-radioisotope of 99mTc and 123I, and its performance was evaluated. The counter consists of four detector panels. Each detector panel consists of two detector modules, and each module has $16\,\, {\times } \,\, 16$ CdTe detector pixels with a pitch of 2.5 mm; the eight detector modules give our system a field of view ( $ {x} {\times } \,\, {y} {\times } {z}$ ) of $4\,\, {\times } \,\, 4\,\, {\times } \,\, 8$ cm3. The crosstalk correction coefficient $ {{{\alpha }}}$ , which is the ratio of the count rate in the 99mTc-energy window to that in the 123I-energy window, was obtained by measuring the single-radioisotope solution of 123I. When the dual-radioisotope of 99mTc and 123I was measured, the true count rate of 99mTc was obtained by subtracting the crosstalk count rate ( $ {{{\alpha }}} \,\, {\times }$ the count rate of 123I) from the uncorrected count rate of 99mTc. To evaluate the measurement accuracy, dual- and single-radioisotope solutions were measured, and the mean percentage error of the measured count rate of dual-radioisotope solutions to that of the single-radioisotope solution was obtained. The energy resolutions full width at half maximum of the CdTe-based well counter were 6.95% and 6.93% at 140.5 keV and 159 keV, respectively, and were higher than that of a conventional NaI (Tl) scintillation detector (10% at 140.5 keV). The count loss in the CdTe detector was 1.7% at 44 kcps. For the dual-radioisotope measurement, the percentage errors (mean percentage% ± standard deviation%, ${N} \,\, {=}$ 3) of the count rate of 99mTc and 123I at a high count rate (99mTc: 44 kcps, 123I: 28 kcps) were −1.9% ± 0.0% and −3.5% ± 1.1%, respectively. On the other hand, the percentage errors of the count rate of 99mTc and 123I at a low count rate (99mTc: 3 kcps, 123I: 4 kcps) were −0.4% ± 0.3% and 0.2% ± 0.6%, respectively. The CdTe-based well counter measured each concentration of 99mTc and 123I in mixed solutions with high accuracy.

Feasibility of a CdTe-based SPECT for high-resolution low-dose small animal imaging: a Monte Carlo simulation study

Dedicated single-photon-emission computed tomography(SPECT) systems based on pixelated semiconductors such as cadmium telluride(CdTe) are in development to study small animal models of human disease. Inan effort to develop a high-resolution, low-dose system for small animalimaging, we compared a CdTe-based SPECT system and a conventionalNaI(Tl)-based SPECT system in terms of spatial resolution, sensitivity,contrast, and contrast-to-noise ratio (CNR). In addition, we investigatedthe radiation absorbed dose and calculated a figure of merit (FOM) for bothSPECT systems. Using the conventional NaI(Tl)-based SPECT system, weachieved a spatial resolution of 1.66 mm at a 30 mm source-to-collimatordistance, and a resolution of 2.4-mm hot-rods. Using the newly-developedCdTe-based SPECT system, we achieved a spatial resolution of 1.32 mm FWHM ata 30 mm source-to-collimator distance, and a resolution of 1.7-mm hot-rods.The sensitivities at a 30 mm source-to-collimator distance were 115.73 counts/sec/MBq and 83.38 counts/sec/MBq for the CdTe-based SPECT andconventional NaI(Tl)-based SPECT systems, respectively. To comparequantitative measurements in the mouse brain, we calculated the CNR forimages from both systems. The CNR from the CdTe-based SPECT system was 4.41,while that from the conventional NaI(Tl)-based SPECT system was 3.11 whenthe injected striatal dose was 160 Bq/voxel. The CNR increased as a functionof injected dose in both systems. The FOM of the CdTe-based SPECT system wassuperior to that of the conventional NaI(Tl)-based SPECT system, and thehighest FOM was achieved with the CdTe-based SPECT at a dose of 40 Bq/voxelinjected into the striatum. Thus, a CdTe-based SPECT system showedsignificant improvement in performance compared with a conventional systemin terms of spatial resolution, sensitivity, and CNR, while reducing theradiation dose to the small animal subject. Herein, we discuss thefeasibility of a CdTe-based SPECT system for high-resolution, low-dose smallanimal imaging.

Optimal design of anger camera for bremsstrahlung imaging: monte carlo evaluation.

A conventional Anger camera is not adapted to bremsstrahlung imaging and, as a result, even using a reduced energy acquisition window, geometric x-rays represent <15% of the recorded events. This increases noise, limits the contrast, and reduces the quantification accuracy. Monte Carlo (MC) simulations of energy spectra showed that a camera based on a 30-mm-thick BGO crystal and equipped with a high energy pinhole collimator is well-adapted to bremsstrahlung imaging. The total scatter contamination is reduced by a factor 10 versus a conventional NaI camera equipped with a high energy parallel hole collimator enabling acquisition using an extended energy window ranging from 50 to 350 keV. By using the recorded event energy in the reconstruction method, shorter acquisition time and reduced orbit range will be usable allowing the design of a simplified mobile gantry. This is more convenient for use in a busy catheterization room. After injecting a safe activity, a fast single photon emission computed tomography could be performed without moving the catheter tip in order to assess the liver dosimetry and estimate the additional safe activity that could still be injected. Further long running time MC simulations of realistic acquisitions will allow assessing the quantification capability of such system. Simultaneously, a dedicated bremsstrahlung prototype camera reusing PMT–BGO blocks coming from a retired PET system is currently under design for further evaluation.

Comparison of photon counting and conventional scintillation detectors in a pinhole SPECT system for small animal imaging: Monte carlo simulation studies

The photon counting detector based on cadmium telluride (CdTe) or cadmium zinc telluride (CZT) is a promising imaging modality that provides many benefits compared to conventional scintillation detectors. By using a pinhole collimator with the photon counting detector, we were able to improve both the spatial resolution and the sensitivity. The purpose of this study was to evaluate the photon counting and conventional scintillation detectors in a pinhole single-photon emission computed tomography (SPECT) system. We designed five pinhole SPECT systems of two types: one type with a CdTe photon counting detector and the other with a conventional NaI(Tl) scintillation detector. We conducted simulation studies and evaluated imaging performance. The results demonstrated that the spatial resolution of the CdTe photon counting detector was 0.38 mm, with a sensitivity 1.40 times greater than that of a conventional NaI(Tl) scintillation detector for the same detector thickness. Also, the average scatter fractions of the CdTe photon counting and the conventional NaI(Tl) scintillation detectors were 1.93% and 2.44%, respectively. In conclusion, we successfully evaluated various pinhole SPECT systems for small animal imaging.