Emission Tomography Research Articles

Photoinduced Triplet Depletion Allowing Higher-Resolution Afterglow

Afterglow emission allows for imaging that is independent of autofluorescence under ambient conditions. Although higher-resolution afterglow is required for increasing the quality of the autofluorescence-free emission imaging, increasing the excitation intensity to generate brighter afterglow emission decreases the resolution of afterglow images. Therefore, methods and materials that provide afterglow imaging with higher resolution remain to be developed. In this study, we performed photoinduced triplet depletion and demonstrated improved resolution of bright afterglow emission using the depletion. Triplet depletion is related to charge separation via photoionization from a triplet state caused by depletion and subsequent rapid singlet formation. Triplet excitons that accumulated in a solid material by excitation were depleted under irradiation using a depletion beam with a longer wavelength than the absorption wavelength of the material. A higher-resolution afterglow image with an improvement of 25% was obtained by simultaneously focusing a donut-shaped depletion beam and an excitation beam.

Influence of interface roughness and rock type on mixed mode fracture characteristics of tunnel shotcrete-rock interface

A four-point shear (FPS) test was conducted to investigate the mixed mode fracture characteristics of the shotcrete-rock interface. Real-time monitoring of the fracture process was achieved using acoustic emission (AE) and digital image correlation (DIC) techniques. The mechanical test results indicate that residual stress increases with modal Angle or roughness under the same crack mouth opening displacement (CMOD). As the modal angle increases, the crack morphology and damage mechanism of the granite-shotcrete interface change. For large modal angles, the crack expands into the granite during the expansion process, leading to a larger range of granite damage at the interface. The results obtained through the nearest neighbor method reveal that specimens with small mode angle, low roughness or weak material properties on one side do not exhibit obvious background events, whereas the cluster characteristics of density distribution are evident. The AE events with smaller nearest neighbor distances were found to be concentrated around the macroscopic cracks. Moreover, the modal angle was observed to have a significant impact on crack opening/sliding displacement, with crack mouth sliding displacement (CMSD) and crack tip sliding displacement (CTSD) both increasing significantly as the modal angle increases.

Collimator design for gamma-ray cascade angular correlations in medical imaging

In recent decades, Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET) have become workhorses of molecular imaging. The main drawback of these modalities is that they resort to statistical methods of image reconstruction, as the location of the individual nuclei emitting radiation is not accessible. To remedy this situation, we embarked on a project to introduce a new modality of nuclear medical imaging which exploits the non-collinear angular correlations of nuclear gamma-ray cascades subsequent to beta decays. This modality, if effective, determines the location of each decay nucleus. We have retrofitted the small animal PET assembly of RIKEN-Kobe (Japan) with tungsten+PLA (polylactic acid) collimators. The chosen material is inexpensive, amenable to three-dimensional (3D) printing, and has good photon attenuation properties. We included the collimator geometry in GATE (Geant4 Application for Tomographic Emission) simulations and developed algorithms for image reconstruction with medical isotope candidates viz., 111In and 43K. Our preliminary simulations show that data acquisition with a 2 MBq source for 900 s is sufficient to reproduce the source geometry with high resolution. This report summarizes our progress to date and the plans for the near future.

Giant Impacts and Debris Disk Morphology

Certain debris disks have nonaxisymmetric shapes in scattered light which are unexplained. The appearance of a disk depends on how its constituent Keplerian ellipses are arranged. The more the ellipses align apsidally, the more nonaxisymmetric the disk. Apsidal alignment is automatic for fragments released from a catastrophic collision between solid bodies. We synthesize scattered light images, and thermal emission images, of such giant impact debris. Depending on the viewing geometry, and if and how the initial apsidal alignment is perturbed, the remains of a giant impact can appear in scattered light as a one-sided or two-sided “fork,” a lopsided “needle,” or a set of “double wings.” The last shape is difficult to reproduce in other scenarios involving gravitational forcing or gas drag, which do not align orbits as well. We compare our images with observations and offer a scorecard assessing whether the scattered light asymmetries in HD 15115, HD 32297, HD 61005, HD 111520, HD 106906, β Pic, and AU Mic are best explained by giant impacts, gravitational perturbations, or sculpting by the interstellar medium.

Crack evolution characteristics of cemented-gangue–fly-ash backfill with different proportions of fly ash and cement

To explore the strength boundaries and corresponding failure characteristics of the backfill body, the basic bearing capacity and failure performance of cemented-gangue–fly-ash backfill (CGFB) with different ratios of fly ash to cement in the binder (F/C) were tested using a uniaxial compressive stress experiment, acoustic emission, and digital image correlation. The results indicate that CGFB has an upper-limit strength of 15.35 MPa, and the strength varies significantly from F/C 0.5 to 2. With the increase in F/C, the brittleness of CGFB decreases. The change in failure mode from tensile accounts for 69.7%, and the change in failure mode to shear accounts for 70.66%. When F/C is low, the crack initiation stress is approximately 0.4–0.5 the peak strength, the crack development is concentrated in the middle of the entire bearing stage, and the scale of the crack is large and develops along the main crack. With the increase in F/C, the initiation stress of the crack decreases to 0.25–0.4 the peak strength, and the development of cracks begins to concentrate in the early and late stages during the loading stage. The scale of the crack is smaller than when F/C is low, and the failure is scattered throughout the specimen.

Field electron emission and field ion microscope images of layered material MoS2

Field emission microscopy and field ion microscopy (FEM and FIM) of two-dimensional layered material, MoS2, were carried out. MoS2 field emitters were prepared by mechanical peeling of a single crystal and by deposition of MoS2 suspension. FEM exhibited an array of elongated broad spots, and the corresponding FIM images presented patterns consisting of streaked spots and split spots (double spots), depending on electric voltages applied to the emitter. Since the probability of field ionization of imaging gas atoms (Ne gas was used in the present study) is governed by both field strength near surface atomic sites and accessible vacant electronic states, these patterns reflect the atomic site and/or spatial distribution of unoccupied electronic orbitals at the edges of MoS2 layers.

Commissioning and dosimetric validation of a novel compensator-based Co-60 IMRT system for evaluating suitability to automated treatment planning.

A novel compensator-based system has been proposed which delivers intensity-modulated radiation therapy (IMRT) with cobalt-60 beams. This could improve access to advanced radiotherapy in low- and middle-income countries. For this system to be clinically viable and to be adapted into the Radiation Planning Assistant (RPA), being developed to offer automated planning services in low- and middle-income countries, it is necessary to commission and validate it in a commercial treatment planning system (TPS). The novel treatment device considered here employs a cobalt-60 source and nine compensators. Each compensator is produced by 3-D printing a thin plastic mold which is then filled on-demand within the machine with reusable 2-mm-diameter spherical tungsten balls. This system was commissioned in the Eclipse TPS and validation tests were conducted with Monte Carlo using Geant4 Application for Tomographic Emission for percentage depth dose, in-plane profiles, penumbra, and IMRT dose validation. And the American Association of Physicists in Medicine Task Group 119 benchmarking testing was performed. Additionally, compensator-based cobalt-60 IMRT plans were created for 46 head-and-neck cancer cases and compared to the linac-based volumetric modulated arc therapy (VMAT) plans used clinically, then dosimetric parameters were evaluated. Beam-on time for each field was calculated. In addition, the measurement was also performed in a limited environment and compared with the Monte Carlo simulations. The differences in percent depth doses and in-plane profiles between the Eclipse and Monte Carlo simulations were 0.65%±0.41% and 1.02%±0.99%, respectively, and the 80%-20% penumbra agreed within 0.46±0.27mm. For the Task Group 119 validation plans, all treatment planning goals were met and gamma passing rates were>95% (3%/3mm criteria). In 46 clinical head-and-neck cases, the cobalt-60 compensator-based IMRT plans had planning target volume (PTV) coverages similar to linac-based VMAT plans: all dosimetric values for PTV were within 1.5%. The organs at risk dose parameters were somewhat higher in cobalt-60 compensator-based IMRT plans versus linac-based VMAT plans. The mean dose differences for the spinal cord, brain, and brainstem were 4.43±1.92, 3.39±4.67, and 2.40±3.71Gy, while those for the rest of the organs were<1Gy. The average beam-on time per field was 0.42±0.10min for the 6 MV multi-leaf-collimator plans while those for the cobalt-60 compensator plans were 0.17±0.01 and 0.31±0.01min at the dose rates of 350 and 175 cGy/min. There was a good agreement between in-plane profiles from measurements and Monte Carlo simulations, which differences are 1.34±1.90% and 0.13±2.16% for two different fields. A novel compensator-based IMRT system using cobalt-60 beams was commissioned and validated in a commercial TPS. Plan quality with this system was comparable to that of linac-based plans in all test cases with shorter estimated beam-on times. This system enables reliable, high-quality plans with reduced cost and complexity and may have benefits for underserved regions of the world. This system is being integrated into the RPA, a web-based platform for auto-contouring and auto-planning.

Feasibility of size-specific organ-dose estimates based on water equivalent diameter for common head CT examinations: a Monte Carlo study

Computed tomography dose index (CTDI) is an unreliable dose estimate outside of the standard CTDI phantom diameters (16 and 32 cm). Size-specific dose estimate (SSDE) for head computed tomography (CT) examination was studied in the American Association of Physicists in Medicine Report 293 to provide SSDE coefficient factors based on water equivalent diameter as size metrics. However, it is limited to one protocol and for a fully irradiated organ. This study aimed to evaluate the dependency of normalized organ dose (ND) on water equivalent diameter as a size metric in three common protocols: routine head, paranasal sinus, and temporal bone. CTDIw measurements were performed for outlined protocols in the Siemens Emotion 16-slice-configuration scanner. Geant4 Application for Tomographic Emission Monte Carlo simulation platform, coupled with ten GSF patient models, was used to estimate organ doses. CT scanner system was modeled. Helical CT scans were simulated using constructor scan parameters and calculated scan lengths of each patient model. Organ doses provided by simulations were normalized to CTDIvol. The water equivalent diameters (D w) of patient models were obtained via relationships between D w and both effective diameter for a sample of patients’ data.NDs received by fully, partially, and non-directly irradiated organs were then reported as a function of D w. For fully irradiated organs, brain (R 2 > 0.92), eyes (R 2 > 0.88), and eye lens (R 2 > 0.89) correlate well with D w. For the rest of the results, a poor correlation was observed. For partially irradiated organs, the exception was scalp (R 2 = 0.93) in temporal bone CT. For non-directly irradiated organs, the exception was thyroid (R 2 > 0.90) and lungs (R 2 > 0.91) in routine head CT. ND correlates well in routine head CT than other protocols. For the most part, no relationship seems to exist between R 2 and scan percentage coverage. The results have revealed additional factors that may influence the ND and D w relationship, which explains the need for more studies in the future to investigate the effect of scan conditions and organ anatomy variation.

Novel 4,4′-Binaphthalimidyl derivatives with carboxyalkyl side chains: Synthesis, Aggregation-induced emission, Hydrogel and Cell imaging

The introduction of aryl groups and/or alkyl side chains to the periphery of a conjugated skeleton can modulate the pattern of molecular aggregation in solution and facilitate its aggregation-induced emission (AIE) performance. In this study, novel three compounds of 4,4′-binaphthalimidyl derivatives (BNICn) were synthesized successfully in which two 1,8-naphthalimide (NI) units were connected by a rotatable single bond at their 4-sites, and two carboxyalkyl chains (number of carbon atoms in the carboxyalkyl chains (n) = 2, 6, and 11) were linked with the nitrogen atoms of NI. BNICn has weakly fluorescent in dilute solutions but become highly emissive in aggregate states. Interestingly, they exhibited carboxyalkyl-dependent AIE properties. The AIE performance of BNIC2 with the shortest carboxyalkyl chain is the strongest among those of the three compounds. The aggregation was also confirmed by the dynamic light scattering (DLS) tests. Moreover, the fluorescence intensities enhanced with the increasing viscosity of the solutions, verifying that the restriction of intramolecular motions (RIM) leads to the occurrence of AIE. Furthermore, the interactions such as π-π stacking of NI groups, and the intermolecular hydrogen-bonding of the carboxyl groups at the terminal of the side chains of BNICn was respectively verified by 1H NMR and FTIR. Thus, a possible self-assemble mode of BNICn is that the stacking NI segments of BNICn are located by the intermolecular hydrogen bonds of carboxyl groups at the terminal of the side chains of BNICn enacting an anchor-like role during aggregation process. For BNIC2 with carboxymethyl group, the shortest spacer of methylene group resulted in more effectively restriction for the intramolecular vibration and rotation, leading to a more efficient AIE performance. Meanwhile, BNIC11 can form thermal-reversible fluorescence hydrogel with ethylenediamine as well as BNIC2 can be applied in cellular imaging. Thus, an effective strategy to achieve and adjust the AIE performance of NI derivatives is proposed.

Evaluation of the Diagnostic Performance of F18-Fluorodeoxyglucose-Positron Emission Tomography, Dynamic Susceptibility Contrast Perfusion, and Apparent Diffusion Coefficient in Differentiation between Recurrence of a High-grade Glioma and Radiation Necrosis.

Differentiation between recurrence of brain tumor and radiation necrosis remains a challenge in current neuro-oncology practice despite recent advances in both radiological and nuclear medicine techniques. The purpose of this study was to compare the diagnostic performance of dynamic susceptibility contrast (DSC) perfusion magnetic resonance imaging (MRI), apparent diffusion coefficient (ADC) derived from diffusion-weighted imaging, and F18-fluorodeoxyglucose-positron emission tomography (F18-FDG-PET) in the differentiation between the recurrence of a high-grade glioma and radiation necrosis. Patients with a diagnosis of high-grade glioma (WHO Grades III and IV) who had undergone surgical resection of the tumor followed by radiotherapy with or without chemotherapy were included in the study. DSC perfusion, diffusion-weighted MRI, and PET scan were acquired on a hybrid PET/MRI scanner. For each lesion, early and delayed tumor-to-brain ratio (TBR), early and delayed maximum standardized uptake value (SUVmax), normalized ADC ratio, and normalized relative cerebral blood volume (rCBV) ratio were calculated and the pattern of lesional enhancement was noted. The diagnosis was finalized with either histopathological examination or the characteristics on follow-up imaging. The statistical analysis using the receiver operator characteristic curves was done to determine the diagnostic performance of DSC perfusion, 18-F FDG-PET, and ADC in differentiation between tumor recurrence and radiation necrosis. Fifty patients were included in the final analysis, 32 of them being men (64%). A cutoff value of early TBR >0.8 (sensitivity of 100% and specificity of 80%), delayed TBR >0.93 (sensitivity of 92.3% and specificity of 80%), early SUVmax >10.2 (sensitivity of 76.9% and specificity of 80%), delayed SUVmax >13.2 (sensitivity of 61.54% and specificity of 100%), normalized rCBV ratio >1.21 (sensitivity of 100% and specificity of 60%), normalized ADC ratio >1.66 (sensitivity of 38.5% and specificity of 80%), and Grade 3 enhancement (sensitivity of 100% and specificity of 60%) were found to differentiate recurrence from radiation necrosis. Early TBR had the highest accuracy (94.44%), while ADC ratio had the lowest accuracy (50%). A combination of early TBR (cutoff value of 0.8), late TBR (cutoff value of 0.93), and rCBV ratio (cutoff value of 1.21) showed a sensitivity of 100%, specificity of 92.3%, positive predictive value of 88.9%, negative predictive value of 93.7%, and an accuracy of 96.6% in discrimination between radiation necrosis and recurrence of tumor. F18-FDG-PET and DSC perfusion can reliably differentiate tumor recurrence from radiation necrosis, with early TBR showing the highest accuracy. ADC demonstrates a low sensitivity, specificity, and accuracy in differentiating radiation necrosis from recurrence. A combination of early TBR, delayed TBR, and rCBV may be more useful in discrimination between radiation necrosis and recurrence of glioma, with this combination showing a better diagnostic performance than individual parameters or any other combination of parameters.

A Rare Case of Asymmetric Progressive Supra Nuclear Palsy Diagnosed In vivo with Magnetic Resonance/Positron Emission Tomography.

PSP and CBD are usually multi system sporadic disorders characterized by tau inclusions in neurons and glia. The clinical and neuroimaging features are different .However in some cases overlapping of features are noted. Here we present a case of a 65 years old female patient, presenting a 3 years history of insidious onset of asymmetric right upper and lower limb dystonia, followed by slowness, falls and injuries to the back, Parkinsonism, urinary incontinence and cognitive dysfunction and upward gaze palsy. MRI findings were suggestive of moderate cerebral and cerebellar atrophy with prominent ventricular system, reduced antero-posterior midline midbrain diameter, at the level of superior colliculus on axial imaging (morning glory sign was positive) on the left side. PET showed asymmetric hypo metabolism noted in the left superior and middle frontal gyrus, superior temporal and mid temporal gyrus in addition to striatum and thalamus, as well as midbrain, pons and right cerebellar hemisphere. Overall MR/PET was suggestive of unilateral PSP (left) and it corroborated with clinical history of unilateral dystonia and supranuclear gaze palsy. Based on MRI the differential considered was also CBD, but PET showed metabolic activity in the motor cortex. Additionally based on the hummingbird sign and morning glory sign a rare diagnosis of unilateral PSP could be made which also corroborated with the clinical picture.The case report emphasizes the utility of PETMRI simultaneously in situations like these to pick atypical variants or cases with overlapping pathology to reach a diagnosis with in vivo imaging methods.

What is the Best Preoperative Quantitative Indicator to Differentiate Primary Central Nervous System Lymphoma from Glioblastoma?

The role of surgery in primary central nervous system lymphoma (PCNSL) is to allow pathological diagnosis from tumor biopsy. However, PCNSL is often difficult to distinguish from other tumors, particularly glioblastoma multiforme (GBM). Quantitative evaluations to facilitate differentiation between PCNSL and GBM would be useful. Here, we investigated the best examinations for exact differentiation of PCNSL from GBM among preoperative examinations, including imaging studies and tumor markers. Various examinations were performed for 68 patients with PCNSL , including serum soluble interleukin 2 receptor, β2-microglobulin (MG) in cerebrospinal fluid (CSF), diffusion-weighted imaging, 11C-methionine-positron emission tomography (PET), and 18F-fluorodeoxyglucose (FDG)-PET. These results were compared with findings from 28 patients with consecutive GBM who underwent the same examinations to evaluate the utility and accuracy of different investigations. CSF β2-MG ≥2.0mg/L was relatively specific for PCNSL, offering 95.0% sensitivity and 85.7% specificity. Tumor-to-contralateral normal brain tissue ratio ≥2.4 on 18F-FDG-PET was also quite specific for PCNSL, offering 83.8% sensitivity and 95.2% specificity. No other examinations displayed any significant differences in quantitative differential markers between PCNSL and GBM. Both β2-MG ≥2.0mg/dL in CSF and tumor-to-contralateral normal brain tissue ratio ≥2.4 from 18F-FDG-PET allow quantitative differentiation of PCNSL from GBM, potentially representing clinically useful indicators. These findings could lead to innovative methods for differentiating PCNSL from GBM as well as new treatment strategies for other brain tumors.

The X-ray synchrotron rims in Cassiopeia A narrow with energy

Context. Some young supernova remnants exhibit thin filaments of X-ray synchrotron radiation coinciding with the forward shock due to accelerated electrons interacting with the local magnetic field. The two main models accounting for the radial brightness evolution of these filaments differ in their prediction of the narrowing (or not) of the filaments with increasing photon energy. Aims. In this paper, we report our observation of such a narrowing of the synchrotron filaments in Cassiopeia A at X-ray energies, and how this finding could inform our understanding of the mechanisms at stake in their formation. Methods. We used a new blind-source-separation method on the 1 Ms Chandra observation of Cassiopeia A in order to obtain detailed and unpolluted images of the synchrotron emission in three energy bands. We then extracted the profiles of several filaments at the forward shock and the reverse shock to estimate and compare their widths. Results. We find that there is indeed a narrowing with energy of the synchrotron filaments both at the forward and at the reverse shocks in Cassiopeia A. The energy dependency of this narrowing seems stronger at high energy, which is indicative of a damping effect that is also suggested by radio observations.

Workability and mechanical properties analysis of hybrid fibers reinforced self-compacting concrete incorporating recycled aggregates based on acoustic emission technique

This research focused on maximizing the utilization of recycled aggregates to produce hybrid fibers reinforced self-compacting concrete (SCC) suitable for the majority of construction applications. Hybrid fibers, including milling profiled steel fiber with the volume fraction of 1.0 % and polypropylene fiber with the volume fraction of 0.1%, and mineral admixtures were used to improve the mechanical properties and workability of SCC with recycled aggregates, respectively. The influence of recycled coarse aggregate (RCA) and recycled fine aggregate (RFA) in different replacement ratio combinations (25%-0%, 50%-0%, 75%-0%, 100%-0%, 0%-25%, 0%-50%, 25%-25%) on the workability and mechanical properties of hybrid fibers reinforced recycled aggregates SCC (HFRA-SCC) were studied. The acoustic emission (AE) and digital image correlation (DIC) technique were used to monitor the crack development of HFRA-SCC under compression and splitting tensile loading, respectively. Results showed that both RCA and RFA had negative effects on the workability of HFRA-SCC when their replacement ratio exceeded 25% respectively. The mechanical properties of HFRA-SCC decreased with the increase of recycled aggregates replacement ratio as well, while fibers could compensate the strength loss caused by recycled aggregates and significantly increase the toughness of HFRA-SCC. A larger number of AE activities, as well as a sudden spike in cumulative AE energy, could predict the failure of specimen in advance. According to the analysis to the experimental results of this paper, the maximum replacement ratio of recycled aggregates used in HFRA-SCC was proposed.

Relating storm-snow avalanche instabilities to data collected from the Differential Emissivity Imaging Disdrometer (DEID)

Storm-snow avalanches are challenging to forecast due to complex alpine terrain and during rapidly changing weather conditions. They can result in loss of lives and significant economic impact. We describe how a new device that continuously measures with high-frequency snowflake mass, size, density, and type, the Differential Emissivity Imaging Disdrometer (DEID), and show how the DEID can be used to aid avalanche forecasting when coupled with a storm-snow stability model. DEID measurements of snow accumulation, snow water equivalent (SWE), and snow density obtained during seventeen storms taken at the mid-Collins Snow-Study Plot at Alta Ski Area in Utah's Central Wasatch mountain range during winter 2020–2021 show excellent agreement with infrequent manual measurements. Additionally, two new variables, the Shape Density Index (SDI) and Complexity, are proposed and used to classify snowflake habit and estimate storm-snow shear strength. We illustrate how these DEID-derived data can be used to identify layers of concern in the storm snow such as density inversions, in real-time without digging snow pits. Furthermore, the DEID-data are used to run four variations of the SNOw Slope Stability model (SNOSS) for the storms investigated. The results are evaluated with data collected from tilt-board tests, infrasound measurements, and visual observations of avalanches. For a total fourteen storms analyzed, the DEID-driven SNOSS-modeled minimum stability index predicts the general stability of the storm-snow as indicated by observed avalanches, both natural and of unknown cause. The results provide a promising approach for nowcasting instabilities within storm-snow layers with a single instrument.

Design of a Nuclear Monitoring System Based on a Multi-Sensor Network and Artificial Intelligence Algorithm

Nuclear power is a sustainable energy source, but radiation management is required for its safe use. Radiation-detection technology has been developed for the safe management of radioactive materials in nuclear facilities but its performance may vary depending on the size and complexity of the structure of nuclear facilities. In this study, a nuclear monitoring system using a multi-sensor network was designed to monitor radioactive materials in a large nuclear facility. Additionally, an artificial-intelligence-based localization algorithm was developed to accurately locate radioactive materials. The system parameters were optimized using the Geant4 Application for Tomographic emission (GATE) toolkit, and the localization algorithm was developed based on the performance evaluation of the Artificial Neural Network (ANN) and Decision Tree (D-Tree) models. In this article, we present the feasibility of the proposed monitoring system by converging the radiation detection system and artificial intelligence technology.

Mesh modeling of system geometry and anatomy phantoms for realistic GATE simulations and their inclusion in SPECT reconstruction

Objective. Monte-Carlo simulation studies have been essential for advancing various developments in single photon emission computed tomography (SPECT) imaging, such as system design and accurate image reconstruction. Among the simulation software available, Geant4 application for tomographic emission (GATE) is one of the most used simulation toolkits in nuclear medicine, which allows building systems and attenuation phantom geometries based on the combination of idealized volumes. However, these idealized volumes are inadequate for modeling free-form shape components of such geometries. Recent GATE versions alleviate these major limitations by allowing users to import triangulated surface meshes. Approach. In this study, we describe our mesh-based simulations of a next-generation multi-pinhole SPECT system dedicated to clinical brain imaging, called AdaptiSPECT-C. To simulate realistic imaging data, we incorporated in our simulation the XCAT phantom, which provides an advanced anatomical description of the human body. An additional challenge with the AdaptiSPECT-C geometry is that the default voxelized XCAT attenuation phantom was not usable in our simulation due to intersection of objects of dissimilar materials caused by overlap of the air containing regions of the XCAT beyond the surface of the phantom and the components of the imaging system. Main results. We validated our mesh-based modeling against the one constructed by idealized volumes for a simplified single vertex configuration of AdaptiSPECT-C through simulated projection data of 123I-activity distributions. We resolved the overlap conflict by creating and incorporating a mesh-based attenuation phantom following a volume hierarchy. We then evaluated our reconstructions with attenuation and scatter correction for projections obtained from simulation consisting of mesh-based modeling of the system and the attenuation phantom for brain imaging. Our approach demonstrated similar performance as the reference scheme simulated in air for uniform and clinical-like 123I-IMP brain perfusion source distributions. Significance. This work enables the simulation of complex SPECT acquisitions and reconstructions for emulating realistic imaging data close to those of actual patients.

Atmospheric-pressure shock-tube measurements of high-temperature propane laminar flame speed across multiple equivalence ratios

Laminar flame speeds of premixed propane in 21%O2-79% Ar (so-called ”airgon”) were experimentally measured in a shock tube at atmospheric pressure (1 atm±2%) for a range of equivalence ratios (0.5, 0.75, 1, and 1.2) and unburned-gas temperatures (644–1,044 K). Simultaneous side-wall schlieren and end-wall CH* emission imaging was utilized to track the propagation of outwardly expanding laminar flames initiated by laser-induced spark ignition behind reflected shock waves. The linear curvature model with an area-averaged formulation was used to extrapolate laminar flame speeds to zero-stretch. The high-temperature laminar flame speed results were compared with 1D simulations performed using two detailed kinetic models, NUIG 1.3 and Aramco 3.0, and two skeletal models, USC Mech II and San Diego 2016. The experimental results agree with the NUIG 1.3 model within 3.5%, while the predictions of the models disagree by up to 16%. Sensitivity analyses conducted using the models revealed six chemical reactions that strongly impact the prediction of laminar flame speed. In order for the present data to be compatible with practical combustion systems using air as the oxidizer, the propane/airgon measurements were scaled to obtain laminar flame speeds of propane/air using ratios calculated from 1D simulations. The scaled experimental measurements showed good agreement with literature propane/air results at 650 K. Empirical correlations of laminar flame speed as a function of unburned-gas temperature are then reported for the studied equivalence ratios.

Mechanisms of ultrafast GHz burst fs laser ablation.

Gigahertz (GHz) femtosecond (fs) lasers have opened possibilities for enhancing and controlling the laser machining quality to engineer the physicochemical properties of materials. However, fundamental understanding of laser-material interactions by GHz fs laser has remained unsolved due to the complexity of associated ablation dynamics. Here, we study the ablation dynamics of copper (Cu) by GHz fs bursts using in situ multimodal diagnostics, time-resolved scattering imaging, emission imaging, and emission spectroscopy. A combination of probing techniques reveals that GHz fs bursts rapidly remove molten Cu from the irradiated spot due to the recoil pressure exerted by following fs pulses. Material ejection essentially stops right after the burst irradiation due to the limited amount of remnant matter, combined with the suppressed heat conduction into the target material. Our work provides insights into the complex ablation mechanisms incurred by GHz fs bursts, which are critical in selecting optimal laser conditions in cross-cutting processing, micro/nano-fabrication, and spectroscopy applications.

Subclinical rib fractures detected by SPECT/CT imaging in a patient with chest wall pain following a car accident

Background: Hairline rib fracture commonly happens after blunt trauma, and it is hard to be detected by X-ray. Many methods can be used, and among them, the hybrid image of single-photon emission computed tomography (SPECT) and computed tomography (CT) seems to produce higher sensitivity for diagnosis. Case presentation: A 63-year-old man came to our rehabilitation clinic after a vehicle accident 25 days earlier. He had multiple plain films focusing in injured areas, but nothing was detected. However, he persisted in pain in the right and left chest walls individually before and after, which worsened every time when he coughed and bent over. Patient was examined with whole body bone scan and SPECT/CT, and showed out the definite fracture of right ribs 3-4 and left ribs 8-10. The patient then received medicine for pain-killer and rehabilitation modalities at the chest wall. Conclusions: We present a patient with a subclinical rib fracture initially, which is later diagnosed by the hybrid images of SPECT/CT. We conclude that hybrid images of SPECT/CT produces more precise diagnoses for the hairline rib fracture in field of scintigraphic rehabilitation.