Instability indices and forecasting thunderstorms: the case of 30 April 2009

In this paper, one meteorological case study for two Iranian airports are presented. Attempts have been made to study the predefined threshold amounts of some instability indices such as vertical velocity and relative humidity. Two important output variables from a numerical weather prediction model have been used to survey thunderstorms. The climatological state of thunder days in Iran has been determined to aid in choosing the airports for the case studies. The synoptic pattern, atmospheric thermodynamics and output from a numerical weather prediction model have been studied to evaluate the occurrence of storms and to verify the threshold instability indices that are based on Gordon and Albert (2000) and Miller (1972). <br><br> Using data from the Statistics and Data Center of the Iran Meteorological Organization, 195 synoptic stations were used to study the climatological pattern of thunderstorm days in Iran during a 15-yr period (1991–2005). Synoptic weather maps and thermodynamic diagrams have been drawn using data from synoptic stations and radiosonde data. A 15-km resolution version of the WRF numerical model has been implemented for the Middle East region with the assistance of global data from University Corporation for Atmospheric Research (UCAR). <br><br> The Tabriz airport weather station has been selected for further study due to its high frequency of thunderstorms (more than 35 thunderstorm days per year) and the existence of an upper air station. Despite the fact that storms occur less often at the Tehran weather station, the station has been chosen as the second case study site due to its large amount of air traffic. Using these two case studies (Tehran at 00:00 UTC, 31 April 2009 and Tabriz at 12:00 UTC, 31 April 2009), the results of this research show that the threshold amounts of 30 °C for KI, −2 °C for LI and −3 °C for SI suggests the occurrence and non-occurrence of thunderstorms at the Tehran and Tabriz stations, respectively. The WRF model output of vertical velocity and relative humidity are the two most important indices for examining storm occurrence, and they have a numerical threshold of 1 m s<sup>−1</sup> and 80%, respectively. These results are comparable to other studies that have examined thunderstorm occurrence

Is metal artefact reduction mandatory in cardiac PET/CT imaging in the presence of pacemaker and implantable cardioverter defibrillator leads?

Abstract Purpose Cardiac PET/CT imaging is often performed in patients with pacemakers and implantable cardioverter defibrillator (ICD) leads. However, metallic implants usually produce artefacts on CT images which might propagate to CTbased attenuation-corrected (CTAC) PET images. The impact of metal artefact reduction (MAR) for CTAC of cardiac PET/ CT images in the presence of pacemaker, ICD and ECG leads was investigated using both qualitative and quantitative analysis in phantom and clinical studies. Methods The study included 14 patients with various leads undergoing perfusion and viability examinations using dedicated cardiac PET/CT protocols. The PET data were corrected for attenuation using both artefactual CT images and CT images corrected using the MAR algorithm. The severity and magnitude of metallic artefacts arising from these leads were assessed on both linear attenuation coefficient maps (μ-maps) and attenuation-corrected PET images. CT and PET emission data were obtained using an anthropomorphic thorax phantom and a dedicated heart phantom made in-house incorporating pacemaker and ICD leads attached at the right ventricle of the heart. Volume of interest-based analysis and regression plots were performed for regions related to the lead locations. Bull's eye view analysis was also performed on PET images corrected for attenuation with and without the MAR algorithm. Results In clinical studies, the visual assessment of PET images by experienced physicians and quantitative analysis did not reveal erroneous interpretation of the tracer distribution or significant differences when PET images were corrected for attenuation with and without MAR. In phantom studies, the mean differences between tracer Nucl Med Mol Imaging (2011) 38:252-262 DOI 10.1007/s00259-010-1635 uptake obtained without and with MAR were 10.16±2.1% and 6.86±2.1% in the segments of the heart in the vicinity of metallic ICD or pacemaker leads, and were 4.43±0.5% and 2.98±0.5% in segments far from the leads. Conclusion Although the MAR algorithm was able to effectively improve the quality of μ-maps, its clinical impact on the interpretation of PET images was not significant. Therefore cardiac PET images corrected for attenuation using CTAC in the presence of metallic leads can be interpreted without correction for metal artefacts. It should however be emphasized that in some special cases with multiple ICD leads attached to the myocardium wall, MAR might be useful for accurate attenuation correction. Eur

The influence of using different reconstruction algorithms on sensitivity of quantitative 18F-FDG-PET volumetric measures to background activity variation

Introduction: This study aims to investigate the influence of background activity variation on image quantification in differently reconstructed PET/CT images. Methods: Measurements were performed on a Discovery-690 PET/CT scanner using a custom-built NEMA-like phantom. A background activity level of 5.3 and 2.6 kBq/ml 18F-FDG were applied. Images were reconstructed employing four different reconstruction algorithms: HD (OSEM with no PSF or TOF), PSF only, TOF only, and TOFPSF, with Gaussian filters of 3 and 6.4 mm in FWHM. SUVmax and SUVpeak were obtained and used as cut-off thresholding; Metabolic Tumor Volume (MTV) and Total Lesion Glycolysis (TLG) were measured. The volume recovery coefficients (VRCs), the relative percent error (�MTV), and Dice similarity coefficient were assessed with respect to true values. Results: SUVmax and SUVpeak decreased and MTV increased as function of increasing the background dose. The most differences occur in smaller volumes with 3-mm filter; Non-TOF and Non-PSF reconstruction methods were more sensitive to increasing the background activity in the smaller and larger volumes, respectively. The TLG values were affected in the small lesions (decrease up to 12). In a range of target volumes, differences between the mean �MTV in the high and low background dose varied from -11.8 to 7.2 using SUVmax and from 2.1 to 7.6 using SUVpeak inter reconstruction methods. Conclusion: The effect of the background activity variation on SUV-based quantification in small lesion was more noticeable than large lesion. The HD and TOFPSF algorithms had the lowest and the highest sensitivity to background activity, respectively. © 2018 Iranian Journal of Nuclear Medicine. All Rights Reserved

Is correction for metallic artefacts mandatory in cardiac SPECT/CT imaging in the presence of pacemaker and implantable cardioverter defibrillator leads?

Introduction: Metallic artifacts due to pacemaker/ implantable cardioverter defibrillator (ICD) leads in CT images can produce artifactual uptake in cardiac SPECT/CT images. The aim of this study was to determine the influence of the metallic artifacts due to pacemaker and ICD leads on myocardial SPECT/CT imaging. Methods: The study included 9 patients who underwent myocardial perfusion imaging (MPI). A cardiac phantom with an inserted solid defect was used. The SPECT images were corrected for attenuation using both artifactual CT and CT corrected using metal artifact reduction (MAR). VOI-based analysis was performed in artifactual regions. Results: In phantom studies, mean-of-relative-difference in white-region, between artifact-free attenuation-map without/with MAR were changed from 9.2 and 2.1 to 3.7 and 1.2 for ICD and pacemaker lead, respectively. However, these values for typical patient were 9.7±7.0 and 3.8±2.4 for ICD and pacemaker leads respectively, in white-region. MAR effectively reduces the artifacts in white-regions while this reduction is not significant in black-regions. Conclusion: Following application of MAR, visual and quantification analyses revealed that while quality of CT images were significantly improved, the improvements in the SPECT/CT images were not as pronounced or significant. Therefore cardiac SPECT images corrected for attenuation using CT in the presence of metallic-leads can be interpreted without correction for metal artefacts. © 2018 Tehran University of Medical Sciences. All rights reserved

Deep-JASC: joint attenuation and scatter correction in whole-body 18F-FDG PET using a deep residual network

Objective: We demonstrate the feasibility of direct generation of attenuation and scatter-corrected images from uncorrected images (PET-nonASC) using deep residual networks in whole-body 18F-FDG PET imaging. Methods: Two- and three-dimensional deep residual networks using 2D successive slices (DL-2DS), 3D slices (DL-3DS) and 3D patches (DL-3DP) as input were constructed to perform joint attenuation and scatter correction on uncorrected whole-body images in an end-to-end fashion. We included 1150 clinical whole-body 18F-FDG PET/CT studies, among which 900, 100 and 150 patients were randomly partitioned into training, validation and independent validation sets, respectively. The images generated by the proposed approach were assessed using various evaluation metrics, including the root-mean-squared-error (RMSE) and absolute relative error (ARE ) using CT-based attenuation and scatter-corrected (CTAC) PET images as reference. PET image quantification variability was also assessed through voxel-wise standardized uptake value (SUV) bias calculation in different regions of the body (head, neck, chest, liver-lung, abdomen and pelvis). Results: Our proposed attenuation and scatter correction (Deep-JASC) algorithm provided good image quality, comparable with those produced by CTAC. Across the 150 patients of the independent external validation set, the voxel-wise REs () were � 1.72 ± 4.22, 3.75 ± 6.91 and � 3.08 ± 5.64 for DL-2DS, DL-3DS and DL-3DP, respectively. Overall, the DL-2DS approach led to superior performance compared with the other two 3D approaches. The brain and neck regions had the highest and lowest RMSE values between Deep-JASC and CTAC images, respectively. However, the largest ARE was observed in the chest (15.16 ± 3.96) and liver/lung (11.18 ± 3.23) regions for DL-2DS. DL-3DS and DL-3DP performed slightly better in the chest region, leading to AREs of 11.16 ± 3.42 and 11.69 ± 2.71, respectively (p value < 0.05). The joint histogram analysis resulted in correlation coefficients of 0.985, 0.980 and 0.981 for DL-2DS, DL-3DS and DL-3DP approaches, respectively. Conclusion: This work demonstrated the feasibility of direct attenuation and scatter correction of whole-body 18F-FDG PET images using emission-only data via a deep residual network. The proposed approach achieved accurate attenuation and scatter correction without the need for anatomical images, such as CT and MRI. The technique is applicable in a clinical setting on standalone PET or PET/MRI systems. Nevertheless, Deep-JASC showing promising quantitative accuracy, vulnerability to noise was observed, leading to pseudo hot/cold spots and/or poor organ boundary definition in the resulting PET images. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature

Characterization of scattered radiation profile in volumetric 64 slice CT scanner: Monte Carlo study using GATE

It is commonly understood that scattered radiation in X-ray computed tomography (CT) reduces the CT number and degrades the quality of reconstructed images. This effect is more pronounced in multi detector CT scanners with extended detector aperture mostly using cone-beam configurations, which are much less immune to scatter than fan-beam and single-slice CT scanners. To perform accurate scatter correction, it is essential to characterize scattered radiation in Volumetric CT. As characterization of scattered radiation behavior using experimental measurement is a difficult and time consuming approach, Monte Carlo simulation can be an ideal method. In this study we used Geant4-based simulation package, GATE, to model x-ray photon interactions in the phantom and detector. The Monte Carlo simulation was validated through comparison with experimental measurement data. Thereafter, the effect of different parameters such as tube voltage and phantom material on the scatter profile and Scatter to Primary Ratio (SPR) was calculated. We also compared the simulated SPR curves with experimental data which was measured with array blocker method. The experimental technique assumed to be the gold standard technique. The comparison between simulation and experimental data in SPR showed error less than 5 . The results indicate that the GATE Monte Carlo code is a useful tool for investigation of scattered radiation characterization in CT scanners. Moreover, there is a possibility of take advantage of GATE for simulation of PET and CT scanners in order to simultaneously asses the contribution of scattered radiation in PET/CT scanners. © 2011 IEEE

Numerical simulation of the impact of Anatolian and Caucasus Mountains on the precipitation distribution over the Black Sea

An attempt is made to examine the role of Anatolian and Caucasus mountain ranges in the precipitation distribution over the Black Sea region and to clarify the dynamical and physical mechanisms responsible for precipitation distribution over the region. Existence of a complex topography in the southern and eastern part of the Black Sea region makes it an important region for cyclogenesis. In this study the effect of Anatolian and Caucasus Mountains on the precipitating synoptic systems forming over the Black Sea are investigated. To this end, the Weather Research and Forecasting (WRF) model at 15-km horizontal grid spacing has been used to evaluate the lifetime of a low pressure system that was accompanied with heavy precipitation on 14 March 2009 over the coastal region of the Black Sea. Two experiments were conducted. In the control experiment (CTL), the topographical features of the region were retained. In the sensitivity experiment (EXP), the Anatolian and Caucasus mountain ranges were removed. It is found that in the EXP, some fields including vertical motion, relative vorticity, humidity, geopotential height in low level, cloud water content and precipitation distribution in the region undergo significant changes. As such, in the EXP, the vorticity, and the cut-off low system over the Black Sea intensified. It is also seen that, under favorable conditions for precipitation occurrence, the precipitation intensity in the south and east coasts of the Black Sea decreased and the region of maximum precipitation shifted toward the "Sea of Azov" region, in the direction of the surface southerly winds

The Effect of Naproxen and Prednisolone in the Treatment of Mild to Moderate Carpal Tunnel Syndrome

Background & aim: Carpal tunnel syndrome is the entrapment of the median nerve in carpal tunnel of the wrist. Symptoms of this syndrome are numbness, tingling, weakness or pain in the fingers and wrist. Treatment includes rest, avoiding the many activities available, splints, non-steroidal anti-inflammatory drugs, oral steroids, steroid injection in wrist and surgery. This study compared the effects of oral prednisolone and naproxen (non-steroidal anti-inflammatory drugs) in the treatment of mild to moderate carpal tunnel syndrome. Methods: In the present clinical-trial study, 44 patients who had mild to moderate carpal tunnel syndrome were selected and randomly assigned into two treatment groups: group 1(n = 22) received naproxen 1000 mg daily for 4 weeks and the group 2 (n = 22) received oral prednisolone 20 mg, daily, in the first 2 weeks and 10 mg daily for 2 weeks. The 3 persons of the second group dropped out of treatment. Re-evaluation of treatment outcome was performed 2 months later. Collected data were analyzed using SPSS software. To describe the data, frequency tables were used. Furthermore, the Chi-square test was used to analyze the data. Results: 36(87.8%) of the patients were males and 12.2% were females. The electro diagnostic studies were shown 16 hands (19.5%) normal, 19 hands (23.2%) had mild and 47 (57.3%) had moderate involvement in beginning of treatment. Tingling fingers and pain in the prednisolone group had significantly lower rate than naproxen group (p< 0.05), but the symptoms were not significantly different in the two groups. Conclusion: The effects of treatments, relief of symptoms and the decrease intensity of carpal tunnel syndrome in patients who received prednisolone were more than naproxen

Monte Carlo-based evaluation of inter-crystal scatter and penetration in the PET subsystem of three GE Discovery PET/CT scanners

a b s t r a c t While there is continuing demand for higher resolution in PET systems the technological improvements are still challenged by the presence of inter-crystal scatter (ICS) and inter-crystal penetration phenomena in PET detectors, which play an important role in deterioration of the spatial resolution. Both ICS and penetration have deteriorative impact on spatial resolution of PET scanners because they can lead to inaccurate incident crystal assignments. As such, an understanding of the quantitative behavior of ICS and penetration can be beneficial whether for design of a more optimized PET detection system or for more accurate modeling of ICS and penetration effects within the image reconstruction system matrix in order to enhance the quality of reconstructed images. In this work we analyzed the quantity of ICS and penetrated events in the form of coincidences, in contrast with the other studies that have assessed ICS and penetration in the form of single photons. This was performed in the PET subsystem of three GE whole-body PET/CT scanners: Discovery RX (DRX), Discovery ST (DST), and Discovery STE (DSTE). Furthermore, as a novel study, we discriminated between ICS vs. penetration events. In order to do this, we employed the GATE (Geant4 Application for Tomographic Emission) Monte Carlo (MC) toolkit for our simulations and used our previously validated GATE models of the scanners. Developing an algorithm, purely true coincidences were discriminated from ICS-and/or penetration-induced (ICS-P) coincidences. ICS-P coincidences were also categorized into three groups: group-1 consisted of coincidence event(s) only affected by penetration (one or both). Group-2 includes coincidences where one event is affected by ICS (possibly including penetration), while the other event is not affected by ICS (i.e. penetration or no mispositioning at all). Finally in group-3, both events are affected by ICS (possibly also including penetration). The results showed that the most magnificent quantitative variations of ICS-P occur along radial direction. In DRX, more than 55% of the true coincidences are mispositioned due to ICS and/or penetration when the source is located at the end of the transaxial field of view (FOV). This value for DST and DSTE is about 45%. Incidentally, the results revealed that the quantities of ICS-P coincidences in the DST and DSTE are almost equal, while there is much smaller ICS-P in the DRX