Energy Window Research Articles

Accuracy versus predictive power in nuclear mass tabulations

The nuclear mass evaluations have been brought into quite an accurate level with the advent of machine learning, while their extrapolations are in great debate as manifested by the large discrepancies between themselves. Here, we present a possible way to heal these existing differences and raise the predictive ability of mass formulas through performing the multi-objective optimization aimed at both the binding energy and the $\ensuremath{\alpha}$ decay energy. As exemplified by the microscopically inspired Dulfo-Zuker model, the Pareto optimal solutions are found to guarantee the robust mass predictions especially towards the extreme neutron-rich nuclei plus the coherent statistical analysis. Besides effectively avoiding the overfitting problem, our results shed new light on narrowing the window of symmetry energy in nuclear mass formulas serving not only the reliable nuclear dripline but also the stringent equation of state in asymmetric nuclear matter.

Outcomes following transarterial radioembolization with 90Y and nanoparticles loaded resin microspheres

90Y bremsstrahlung Single-Photon Emission Tomography (SPECT) imaging is employed to check the possibility of extrahepatic uptake and the quantification of delivered dose in Transarterial Radioembolization (TARE). 90Y bremsstrahlung SPECT imaging is challenging due to the nature of bremsstrahlung photons. We reported a Monte Carlo study using the resin microspheres loaded with 90Y and Nanoparticles (NPs) in the TARE. By injection of Bismuth (Bi) and Europium (Eu) NPs into the resin microspheres, the sensitivity and the contrast to noise ratio increased for the bremsstrahlung planar images. The highest signal to background ratio was observed in the characteristic X-ray planar images taken with the energy window at the Kα1 ± 10 keV when Eu NPs were incorporated into the microsphere. The dose enhancement ratio decreased dramatically at NP concentrations >2.4 M. Incorporating NPs into the resin microspheres improves the quality of post-treatment images and establishes a standardized imaging protocol for post-treatment imaging by characteristic X-rays.

Quantitative SPECT/CT imaging of lead-212: a phantom study

BackgroundLead-212 (212Pb) is a promising radionuclide for targeted therapy, as it decays to α-particle emitter bismuth-212 (212Bi) via β-particle emission. This extends the problematic short half-life of 212Bi. In preparation for upcoming clinical trials with 212Pb, the feasibility of quantitative single photon-emission computed tomography/computed tomography (SPECT/CT) imaging of 212Pb was studied, with the purpose to explore the possibility of individualised patient dosimetric estimation.ResultsBoth acquisition parameters (combining two different energy windows and two different collimators) and iterative reconstruction parameters (varying the iterations x subsets between 10 × 1, 15 × 1, 30 × 1, 30 × 2, 30 × 3, 30 × 4, and 30 × 30) were investigated to evaluate visual quality and quantitative uncertainties based on phantom images. Calibration factors were determined using a homogeneous phantom and were stable when the total activity imaged exceeded 1 MBq for all the imaging protocols studied, but they increased sharply as the activity decayed below 1 MBq. Both a 20% window centred on 239 keV and a 40% window on 79 keV, with dual scatter windows of 5% and 20%, respectively, could be used. Visual quality at the lowest activity concentrations was improved with the High Energy collimator and the 79 keV energy window. Fractional uncertainty in the activity quantitation, including uncertainties from calibration factors and small volume effects, in spheres of 2.6 ml in the NEMA phantom was 16–21% for all protocols with the 30 × 4 filtered reconstruction except the High Energy collimator with the 239 keV energy window. Quantitative analysis was possible both with and without filters, but the visual quality of the images improved with a filter.ConclusionsOnly minor differences were observed between the imaging protocols which were all determined suitable for quantitative imaging of 212Pb. As uncertainties generally decreased with increasing iterative updates in the reconstruction and recovery curves did not converge with few iterations, a high number of reconstruction updates are recommended for quantitative imaging.

Reduction of contribution of scattered photons by optimization of energy window settings in 201Tl SPECT imaging: a simulation study

Introduction and Objectives: detection of Compton scattered photons is one of the effective factors in reducing the quality of SPECT images. The aim of this study is to reduce the contribution of scattered counts included in the main energy window for 201Tl SPECT imaging in two steps: first step, by determining the location and width of the optimal main energy window, and second step, by using the optimal correction methods.Materials and Methods: in this study, the Monte Carlo program is used to simulate the required phantoms (a cylindrical phantom consist of two small cylinders with different diameters and a simple cardiac phantom), and to produce the projections related to different energy windows.Results: according to the simulation results, among the 13 investigated energy windows, the 30%-wide window with the central energy of 75 keV is determined as the optimal main window for 201Tl SPECT imaging. Also, from the results of this study, two energy window settings are proposed as the most suitable settings for scatter correction of 201Tl SPECT images. In the first case, a second energy window (a 34%-wide window centered at 51 keV) with counts approximately equal to the scattered counts of the optimal main window, and in the second case, two narrow windows (a 8%-wide window centered at 56 keV and a 6%-wide window centered at 92 keV) on both sides of the optimal main window and at a certain distance from two sides of this window are determined as the most suitable energy window settings for these methods.Conclusion: using the optimal main window together with the optimal scatter correction settings proposed in this study leads to a significant improvement of the contrast of 201Tl SPECT images with an acceptable noise level.

Strengthened spin–valley polarization and negative magnetoresistance based on an asymmetrical double-ferromagnetic WSe2 junction

The spin–valley transport and tunneling magnetoresistance (TMR) are studied in an off-resonant circularly polarized light (CPL)-modulated asymmetrical double-ferromagnetic (FM) WSe 2 junction. Based on the results, we propose a device that can simultaneously operate as spin–valley filter and exhibit giant magnetoresistance in a single system. For the antiparallel configuration, the broken spin degeneracy and optical Stark effect in the first FM barrier produce 100% spin (valley)-polarized particles. Subsequently, the spin valve effect from the second FM barrier gives rise to a 100% spin (valley)-selective polarization in the strengthened polarized energy windows of the first CPL. Furthermore, increasing the asymmetrical magnetization of such a junction is found to substantially enhance the TMR, leading to a positive 100% TMR. The TMR can be tuned from −100% to 100% and is sensitively dependent on the chirality of the second CPL due to the coupling between the spin valve effect and the optical Stark effect. Our findings indicate that double-FM barriers combined with off-resonant CPL modulation can be an excellent option to improve the spin–valley polarization and magnetoresistance of transition metal dichalcogenide-based structures. • A model was proposed to improve the magnetoresistance response as well as obtain two well-defined spin–valley polarization states. • The structure gives rise to a 100% spin (valley)-selective polarization in strengthened polarized energy windows of light. • Increasing the asymmetrical magnetization of this junction is found to substantially enhance the tunnel magnetoresistance to 100%. • The magnetoresistance can be tuned from −100% to 100% and is sensitively dependent on the chirality of light.

Interaction of graphene with Au n clusters: a first-principles study

The interaction between Au n (n = 1–6) clusters and graphene is studied using first-principles simulations, based on density functional theory. The computed binding energy between Au n and graphene depends on the number of atoms in the cluster and lies between −0.6 eV and −1.7 eV, suggesting (weak) chemisorption of the clusters on graphene, rather than physisorption. Overall, the electronic properties, spin–orbit interaction and spin texture, as well as the transport properties of graphene strongly depend on the precise size of the Au n clusters. Doping of graphene is predicted for clusters with an odd number of Au atoms, due to overlap between Au s and carbon pz states close to the Fermi level. On the other hand, there is no charge transfer between even size Au clusters and graphene, but a gap is formed at the Dirac cone, due to the breaking of the pseudo spin inversion symmetry of graphene’s lattice. The adsorbed Au n clusters induce spin–orbit interactions as well as spin and pseudo spin interactions in graphene, as indicated by the splitting of the electronic band structure. A hedgehog spin texture is also predicted for adsorbed clusters with an even number of Au atoms. Ballistic transport simulations are performed to study the influence of the adsorbed clusters on graphene’s electronic transport properties. The influence of the cluster on the electron transmission across the structure depends on the mixing of the valence orbitals in the transport energy window. In the specific case of the Au3/graphene system, the adsorbed clusters reduce the transmission and the conductance of graphene. The Au3 clusters act as ‘scattering centers’ for charge carriers, in agreement with recent experimental studies.

The Effect of an Energy Window with an Ellipsoid Phantom on the Differential Defect Contrast on Myocardial SPECT Images.

Good quality single-photon emission computed tomography (SPECT) images are required to achieve a perfect diagnosis and determine the severity of defects within the myocardial wall. There are many techniques that can support the diagnosis of defect formations in acquired images and contribute to avoiding errors before image construction. The main aim of this study was to determine the effect of energy width (15%, 20%, and 25%) on defect contrast in myocardial SPECT images correlated with the decentralization of positioning of a phantom. A phantom of polyethylene plastic was used to mimic the myocardial wall of the left ventricle. The phantom consists of two chambers, inner and outer. Two rectangular pieces of plastic were placed in anterior and inferior locations in the mid-region of the myocardial phantom to simulate myocardial infarction (defects). The average defect contrast for all phantom positions using 15% to 20% energy was (1.2, 1.6) for the anterior region and (1.1, 2) for the inferior region, respectively. Additionally, the energy window width was >25% with a large displacement of the positioning off center, leading to loss of the defect contrast in myocardial SPECT images, particularly in the inferior region. The study showed decreasing defect contrast in both locations, anterior and inferior, with increasing energy window width correlated with eccentricity positioning of the phantom on an imaging table.

Micropatterned Poly(3,4-ethylenedioxythiophene) Thin Films with Improved Color-Switching Rates and Coloration Efficiency.

Electrochromic materials carry out redox reactions and change their colors upon external bias. These materials are the primary component in constructing smart windows for energy saving in buildings or vehicles. Enhancing the electrochromic performances of the materials is crucial for their practical applications. Micropatterned poly(3,4-ethylenedioxythiophene) (mPEDOT) thin films are electrodeposited on indium tin oxide conducting glass in this study. Their electrochromic properties, including transmittance modulation ability, color-switching rates, and coloration efficiency, are investigated and compared with nonpatterned PEDOT thin films. The mPEDOT thin films exhibited faster coloring and bleaching speeds and higher coloration efficiency than the PEDOT thin films while keeping similar transmittance modulation ability. The results suggest that micropatterning an electrochromic material thin film might enhance its electrochromic performances. This research demonstrates the possibility of promoting the color-switching rate of a PEDOT thin film by micropatterning it.

Improved Passive Gamma Emission Tomography image quality in the central region of spent nuclear fuel

Reliable non-destructive methods for verifying spent nuclear fuel are essential to draw credible nuclear safeguards conclusions from spent fuel. In Finland, spent fuel items are verified prior to the soon starting disposal in a geological repository with Passive Gamma Emission Tomography (PGET), a uniquely accurate method capable of rod-level detection of missing active material. The PGET device consists of two highly collimated detector banks, collecting gamma emission data from a 360° rotation around a fuel assembly. 2D cross-sectional activity and attenuation images are simultaneously computed. We present methods for improving reconstructed image quality in the central parts of the fuel. The results are based on data collected from 2017 to 2021 at the Finnish nuclear power plants with 10 fuel assembly types of varying characteristics, for example burnups from 5.7 to 55 GWd/tU and cooling times from 1.9 to 37 years. Data is acquired in different gamma energy windows, capturing the peaks of Cs-137 (at 662 keV) and Eu-154 (at 1274 keV), abundant isotopes in long-cooled spent nuclear fuel. Data from these gamma energy windows at well-chosen angles are used for higher-quality images, resulting in more accurate detection of empty rod positions. The method is shown to detect partial diversion of nuclear material also in the axial direction, demonstrated with a novel measurement series scanning over the edge of partial-length rods.

AbInitio Prediction of the ^{4}He(d,γ)^{6}Li Big Bang Radiative Capture.

The rate at which helium (^{4}He) and deuterium (d) fuse together to produce lithium-6 (^{6}Li) and a γ ray, ^{4}He(d,γ)^{6}Li, is a critical puzzle piece in resolving the discrepancy between big bang predictions and astronomical observations for the primordial abundance of ^{6}Li. The accurate determination of this radiative capture rate requires the quantitative and predictive description of the fusion probability across the big bang energy window (30 keV≲E≲400 keV), where measurements are hindered by low counting rates. We present first-principle (or, abinitio) predictions of the ^{4}He(d,γ)^{6}Li astrophysical S factor using validated nucleon-nucleon and three-nucleon interactions derived within the framework of chiral effective field theory. By employing the abinitio no-core shell model with continuum to describe ^{4}He-d scattering dynamics and bound ^{6}Li product on an equal footing, we accurately and consistently determine the contributions of the main electromagnetic transitions driving the radiative capture process. Our results reveal an enhancement of the capture probability below 100keV owing to previously neglected magnetic dipole (M1) transitions and reduce by an average factor of 7 the uncertainty of the thermonuclear capture rate between 0.002 and 2GK.

First-principles study on the magnetic and electronic properties of the high-pressure orthorhombic phase of MnSe

Exploring the mechanism of unconventional superconductivity has been one of the most important topics in condensed matter physics, while studying the magnetic and electronic properties of the parent compounds of unconventional superconductors can provide helpful clues. Recently, superconductivity in the orthorhombic-phase MnSe was successfully induced by applying high pressure, which makes MnSe the second Mn-based superconductor after MnP. Based on the spin-polarized density functional theory calculations, we have studied the magnetic and electronic properties of the orthorhombic-phase MnSe under high pressure. We show that there may exist strong antiferromagnetic (AFM) fluctuations in a narrow energy window (less than 3 meV/Mn) among an AFM state dubbed AFM3 and a series of staggered $n$-mer AFM states. Here the $n$-mer means that a set of $n$ adjacent spins on a line are parallelly aligned. In the AFM3 state and the $n$-mer AFM states, the Mn spins show AFM coupling along the $x$ axis and ferromagnetic (FM) coupling along the $y$ axis, but respectively host FM and staggered $n$-mer AFM correlations along the $z$ axis. Our calculations indicate that the orthorhombic-phase MnSe exhibits a metallic behavior in the low-energy magnetic states, in good accordance with the previous experimental observations. We also map the calculated energies onto an effective Heisenberg model and obtain the exchange couplings $J$, whose values can serve as a reference for analyzing the data from magnetic measurements. Two usual mechanisms like Fermi surface nesting and electron-phonon coupling can be ruled out as the origin of superconductivity. The magnetic properties in the orthorhombic-phase MnSe under high pressure need future in-depth experimental examination.

Optimal theranostic SPECT imaging protocol for 223radium dichloride therapy

223Radium dichloride image-based individual dosimetry requires an optimal acquisition and reconstruction protocol and proper image correction methods for theranostic applications. To assess this problem, radium-223 dichloride SPECT images were acquired from a Jaszczak simulator with a dual-headed gamma camera, LEHR collimator, 128 × 128 matrix, and total time of 32 minutes. A cylindrical PMMA phantom was used to calibrate the measurements performed with Jaszczak. The image quality parameters (noise coefficient, contrast, contrast-to-noise ratio and recovery coefficient) and septal penetration correction were calculated by MATLAB®. The best results for the investigated image quality parameters were obtained with an 89 keV energy window (24% wide) produced together with OSEM/MLEM reconstruction (8 subsets and 4 iterations) applying a Butterworth filter (order 10 and cutoff frequency of 0.48 cycles·cm−1). The successfully performed recovery coefficient parameter evaluation allows uptake correction for future patient dosimetry applications.

Performance Evaluation of a PET of 7T Bruker Micro-PET/MR Based on NEMA NU 4-2008 Standards

Purpose: This study aimed to measure the performance evaluation of the Bruker sequential micro-positron emission tomography/magnetic resonance imaging (PET/MRI) scanner by following National Electrical Manufacturers Association (NEMA) NU 4-2008 standards’ protocol. The system consists of a high-performance silicon photomultiplier (SiPM) advanced technology detector and a continuous lutetium-yttrium oxyorthosilicate (LYSO) crystal. Methods: A 22Na (sodium-22) point source was utilized to assess the spatial resolution and system sensitivity, and the Micro-PET scatter phantom measurements were conducted to measure count rate measurements and scatter fractions (SF). A mouse-like Micro-PET image quality (IQ) phantom was utilized as a model to analyze the uniformity, recovery coefficient (RC), and spillover ratio (SOR). A small animal PET/MRI imaging study was performed in a rat. Results: We calculated the spatial resolutions of filtered back-projection (FBP), and used 3D-MLEM to reconstruct PET images at the axial center and ¼ of the axial field of view (FOV) in axial, radial, and tangential directions. The best observed spatial resolutions in both reconstructed images were obtained in the tangential direction, and the values were 0.80 mm in 3D-MLEM and 0.94 mm in FBP. The peak noise equivalent count rate (NECR) in the 358–664 keV energy window was 477.30 kcps at 95.83 MBq and 774.45 kcps at 103.6 MBq for rat and mouse-sized scatter phantoms, respectively. The rat and mouse-sized phantoms scatter fractions (SF) were 14.2% and 6.9%, respectively. Conclusions: According to our results, the performance characteristics of the scanner are high sensitivity, good spatial resolution, low scatter fraction, and good IQ, indicating that it is suitable for preclinical imaging studies.

Phase diagram of chiral magnets via Green’s function method

In this paper, Green’s function method is applied to study the ferromagnetic system with Dzyaloshinkii–Moriya (DM) interaction in both two-dimension (2D) and three-dimension chiral magnets. Relevant properties in 2D magnets are calculated, such as the susceptibility, correlation function and analytical expressions of phase boundary. Based on the theoretical results, a new phase is predicted in the window of strong DM interaction characterized by a negative winding number. In addition, helical state in pure 2D material only appears at zero temperature. The analysis on correlation function shows a special symmetry of transverse spin correlation, which corresponds to the skyrmion phase. The results also prove the instability of helical state and its lifetime is numerically computed. Different from 2D magnets, helical state in 3D exists in the window of a lower Zeeman energy and has a long lifetime. DM interaction also reduces Curie temperature because of the spatial symmetry breaking.

Conformational preferences of endohedral metallofullerenes on Ag, Au, and MgO surfaces: Theoretical studies.

In this report, we study the ordering of C60 , Sc3 N@C80 , and Dy2 ScN@C80 molecules on different metallic and dielectric surfaces such as Ag(100), Au(111), and MgO(100). By using DFT techniques, we can classify different types of cage-to-surface arrangements and their relative energies. Using a proposed homogenous sampling of the conformational space for the M3 N cluster, we determine a potential energy map that is capable of providing a structural distribution for a given energy window. We find that Coulomb interaction is a dominant force that governs the system's stability and order. However, a deep analysis of the charge density rearrangements reveals that even though the integral charges may be considered as a qualitative control parameter, it fails to provide quantitative data due to the importance of spatial characteristics of charge densities.

Experimental characterization of an X-ray photon counting detector

This paper presents the experimental test results of the X-ray photon counting detectors based on our pixel readout ASIC. The chip integrates a 64 × 128 array of pixels in the size of 150 µm × 150 µm and each pixel consists of four 12-bit energy windows. Two types of CdTe detectors have been bump bonded to the ASICs and have been tested.The electronic characteristics of the readout chip were evaluated first by injecting charge through the calibration capacitors. The non-uniformity of the energy thresholds among pixels was measured and then were compensated by tuning the local DACs.The detector performance was then characterized using X-ray tubes. The energy responses of the detectors were measured using the characteristic X-ray of the target materials. The global energy thresholds were then calibrated with these specific energies of photons. Polarization effects under different photon fluxes were also studied. Preliminary imaging was conducted. The detector response under uniform irradiation was investigated. The spatial uniformity of the detectors was analyzed and the flat field correction was then conducted to improve image quality. CT detailed test results will be discussed in this paper.

Fusion and back-angle quasielastic measurements in Si30+Gd156 near the Coulomb barrier

Background: Advancement in accelerator facilities has opened the door to dig deep to understand the interplay between nuclear reactions and structures. Although the influence of inelastic excitations on nuclear scattering and sub-barrier fusion is somewhat established, a clear understanding of nucleon transfer with a positive-$Q$ value is yet to achieve.Purpose: The objective of this paper is to examine the role of the $2n$-transfer channel with a positive $Q$ value on sub-barrier fusion and back-angle quasielastic (QE) scattering in the $^{30}\mathrm{Si}+^{156}\mathrm{Gd}$ reaction. Furthermore, extraction of barrier distributions (BDs) from fusion and QE scattering to infer their shapes is also a prime goal.Method: The excitation functions (EFs) of fusion and back-angle QE scattering have been measured over a wide range of incident beam energy around the Coulomb barrier using a recoil mass spectrometer. Furthermore, BDs have been extracted using the measured fusion and back-scattered QE data. The underlying findings have been analyzed within the framework of coupled-channel (CC) formalism using ccfull and ecc programs.Results: Fusion enhancement has been observed compared to those predicted from the one-dimensional barrier penetration model at sub-barrier energies. Fusion enhancement and QE EFs are explained by CC predictions considering the collective excitations among the colliding nuclei. The inclusion of $2n$ transfer and collective excitations in ccfull improves the fit to the experimental fusion data in a short span of energy window around the Coulomb barrier, whereas no significant effect has been observed at the sub-barrier region. However, no such effect of $2n$-pickup transfer has been observed from ecc model calculations. Thus, no firm conclusion can be made on the role of $2n$-pickup transfer with a positive $Q$ value in present measurements.Conclusion: Fusion EFs have been successfully explained by the CC calculations using ccfull and ecc model codes. No significant effect of the $2n$-pickup channel with a positive $Q$ value was observed on sub-barrier fusion enhancement. However, QE EFs are reproduced by considering the collective excitations and $2n$-transfer channel couplings. Fusion and QE BDs are similar in shape within the experimental uncertainty. One-dimensional barrier parameters extracted from the measured data agree with the different theoretical models. Also, the present system obeys the systematic based on deformation values after transfer at the exit.

Adapting a low-count acquisition of the bone scintigraphy using deep denoising super-resolution convolutional neural network

PurposeDeep-layer learning processing may improve contrast imaging with greater precision in low-count acquisition. However, no data on noise reduction using super-resolution processing for deep-layer learning have been reported in nuclear medicine imaging. ObjectivesThis study was designed to evaluate the adaptability of deep denoising super-resolution convolutional neural networks (DDSRCNN) in nuclear medicine by comparing them with denoising convolutional natural networks (DnCNN), Gaussian processing, and nonlinear diffusion (NLD) processing. MethodsIn this study, 156 patients were included. Data were collected using a matrix size of 256 × 256 with a pixel size of 2.46 mm at 0.898 folds, 15% energy window at the center of the photopeak energy (140 keV), and total count of 1000 kilocounts (kct). Following the training and validation of two learning models, we created 100 images for each 20-test datum. The peak signal-to-noise ratio (PSNR) and structural similarity (SSIM) between each image and the reference image were calculated. ResultsDDSRCNN showed the highest PSNR values for all total counts. Regarding SSIM, DDSRCNN had significantly higher values than the original and Gaussian. In DnCNN, false accumulation was observed as the total counts increased. Regarding PSNR and SSIM transition, the model using 100–500-kct training data was significantly higher than that using 100-kct training data. ConclusionsEdge-preserving noise reduction processing was possible, and adaptability to low-count acquisition was demonstrated using DDSRCNN. Using training data with different noise levels, DDSRCNN could learn the noise components with high accuracy and contrast improvement.

NEMA characterization of the SAFIR prototype PET insert

BackgroundThe SAFIR prototype insert is a preclinical Positron Emission Tomography (PET) scanner built to acquire dynamic images simultaneously with a 7 T Bruker Magnetic Resonance Imaging (MRI) scanner. The insert is designed to perform with an excellent coincidence resolving time of 194 ps Full Width Half Maximum (FWHM) and an energy resolution of 13.8% FWHM. These properties enable it to acquire precise quantitative images at activities as high as 500 MBq suitable for studying fast biological processes within short time frames (< 5 s). In this study, the performance of the SAFIR prototype insert is evaluated according to the NEMA NU 4-2008 standard while the insert is inside the MRI without acquiring MRI data.ResultsApplying an energy window of 391–601 keV and a coincidence time window of 500 ps the following results are achieved. The average spatial resolution at 5 mm radial offset is 2.6 mm FWHM when using the Filtered Backprojection 3D Reprojection (FBP3DRP) reconstruction method, improving to 1.2 mm when using the Maximum Likelihood Expectation Maximization (MLEM) method. The peak sensitivity at the center of the scanner is 1.06%. The Noise Equivalent count Rate (NECR) is 799 kcps at the highest measured activity of 537 MBq for the mouse phantom and 121 kcps at the highest measured activity of 624 MBq for the rat phantom. The NECR peak is not yet reached for any of the measurements. The scatter fractions are 10.9% and 17.8% for the mouse and rat phantoms, respectively. The uniform region of the image quality phantom has a 3.0% STD, with a 4.6% deviation from the expected number of counts per voxel. The spill-over ratios for the water and air chambers are 0.18 and 0.17, respectively.ConclusionsThe results satisfy all the requirements initially considered for the insert, proving that the SAFIR prototype insert can obtain dynamic images of small rodents at high activities (sim 500 MBq) with a high sensitivity and an excellent count-rate performance.

Evaluation of quantitative accuracy among different scatter corrections for quantitative bone SPECT/CT imaging.

Although scatter correction improves SPECT image contrast and thus image quality, the effects of quantitation accuracy under various conditions remain unclear. The present study aimed to empirically define the conditions for the optimal scatter correction of quantitative bone SPECT/CT images. Scatter correction was performed by applying dual and triple energy windows (DEW and TEW) with different sub-energy window widths, and effective scatter source estimation (ESSE) to CT-based scatter correction. Scattered radiation was corrected on images acquired using a triple line source (TLSP) phantom and an uniform cylinder phantom. The TLSP consisted of a line source containing 74.0 MBq of 99mTc in the middle, and a background component containing air, water or a K2HPO4 solution with a density equivalent to that of bone. The sum of all pixels in air, water and the K2HPO4 solution was measured on SPECT images. Scatter fraction (SF) and normalized mean square error (NMSE) based on counts from the air background as a reference were then calculated to assess quantitative errors due to scatter correction. The uniform cylinder phantom contained the same K2HPO4 solution and 222.0 MBq of 99mTc. The coefficient of variation (CV) was calculated from the count profile of this phantom to assess the uniformity of SPECT images across scatter correction under various conditions. Both SF and NMSE in SPECT images of phantoms containing water in the background were lower at a TEW sub-window of 3% (TEW3%), than in other scatter corrections, whereas those in K2HPO4 were lower at a DEW sub-window of 20% (DEW20%). Larger DEW and smaller TEW sub-energy windows allowed more effective correction. The CV of the uniform cylinder phantom, DEW20%, was inferior to all other tested scatter corrections. The quantitative accuracy of bone SPECT images substantially differed according to the method of scatter correction. The optimal scatter correction for quantitative bone SPECT was DEW20% (k = 1), but at the cost of slightly decreased image uniformity.