Calibration improvements expand filterscope diagnostic use

The filterscope diagnostic on DIII-D utilizes photomultiplier tubes to measure visible light emission from the plasma. The system has undergone a substantial upgrade since previous attempts to cross-calibrate the filterscope with other spectroscopic diagnostics were unsuccessful. The optics now utilize a dichroic mirror to initially split the light at nearly 99% transmission or reflectance for light below or above 550 nm. This allows the system to measure Dα emission without degrading visible light emission from the plasma for wavelengths below 550 nm (to measure Dβ, Dγ, W-I, C-III, etc.). Additional optimization of the optical components and calibration techniques reduce the error in the signal up to 10% in some channels compared to previous methods. Cross-calibration measurements with two other high resolution spectroscopic diagnostics now show excellent agreement for the first time. This expands the capabilities of the filterscope system allowing measurement of divertor detachment, emission profiles, edge-localized mode behavior, and plasma-wall interactions. It also enables direct comparisons against calculations from boundary plasma simulations. These were not possible before.

First Evidence of Local E×B Drift in the Divertor Influencing the Structure and Stability of Confined Plasma near the Edge of Fusion Devices

The structure of the edge plasma in a magnetic confinement system has a strong impact on the overall plasma performance. We uncover for the first time a magnetic-field-direction dependent density shelf, i.e., local flattening of the density radial profile near the magnetic separatrix, in high confinement plasmas with low edge collisionality in the DIII-D tokamak. The density shelf is correlated with a doubly peaked density profile near the divertor target plate, which tends to occur for operation with the ion B×∇B drift direction away from the X-point, as currently employed for DIII-D advanced tokamak scenarios. This double-peaked divertor plasma profile is connected via the E×B drifts, arising from a strong radial electric field induced by the radial electron temperature gradient near the divertor target. The drifts lead to the reversal of the poloidal flow above the divertor target, resulting in the formation of the density shelf. The edge density shelf can be further enhanced at higher heating power, preventing large, periodic bursts of the plasma, i.e., edge-localized modes, in the edge region, consistent with ideal magnetohydrodynamics calculations.

E×B Flux Driven Detachment Bifurcation in the DIII-D Tokamak

A bifurcative step transition from low-density, high-temperature, attached divertor conditions to high-density, low-temperature, detached divertor conditions is experimentally observed in DIII-D tokamak plasmas as density is increased. The step transition is only observed in the high confinement mode and only when the B×∇B drift is directed towards the divertor. This work reports for the first time a theoretical explanation and numerical simulations that qualitatively reproduce this bifurcation and its dependence on the toroidal field direction. According to the model, the bifurcation is primarily driven by the interdependence of the E×B-drift fluxes, divertor electric potential structure, and divertor conditions. In the attached conditions, strong potential gradients in the low field side (LFS) divertor drive E×B-drift flux towards the high field side divertor, reinforcing low density, high temperature conditions in the LFS divertor leg. At the onset of detachment, reduction in the potential gradients in the LFS divertor leg reduce the E×B-drift flux as well, such that the divertor plasma evolves nonlinearly to high density, strongly detached conditions. Experimental estimates of the E×B-drift fluxes, based on divertor Thomson scattering measurements, and their dependence on the divertor conditions are qualitatively consistent with the numerical predictions. The implications for divertor power exhaust and detachment control in the next step fusion devices are discussed.

Factors Influencing Confidence in Diagnostic Ratings and Retreatment Recommendations in Coiled Aneurysms

BACKGROUND AND PURPOSE

Angiographic occlusion and retreatment of coiled aneurysms are commonly used as surrogate end points in clinical trials. We aimed to evaluate the influence of aneurysm, patient, and rater characteristics on the confidence of visual evaluation of aneurysm coiling and retreatment decisions.

MATERIALS AND METHODS

Twenty-six participants of the Advanced Course in Endovascular Interventional Neuroradiology of the European Society of Neuroradiology were asked to evaluate digital subtraction angiography examinations of patients who had undergone endovascular coiling, by determining the grade of aneurysm occlusion, the change between immediate postprocedural and follow-up angiograms, their level of confidence, the technical difficulty of retreatment, and the best therapeutic approach. The experience, knowledge, and skills of each participant were assessed. The influence of rater and case characteristics on indicated confidence in diagnostic ratings and retreatment recommendations was analyzed.

RESULTS

Interrater reliability was moderate regarding the assessment of aneurysm occlusion grade (intraclass correlation coefficient = 0.581) and substantial regarding change (intraclass correlation coefficient = 0.776). Overall confidence in the diagnostic rating was high (median, "very certain"). Confidence was statistically significantly higher in cases that were generally rated as "worse." The odds of recommending retreatment were significantly higher in cases that were generally rated with higher mean confidence.

CONCLUSIONS

Although overall confidence in the diagnostic rating was high, our study confirms the suboptimal interrater reliability of visual assessment of aneurysm occlusion as well as retreatment recommendations, rendering both questionable as primary outcome measures. Besides recurrence status, recommendation of retreatment is significantly influenced by patient age, aneurysm neck width, and characteristics of the therapist.

Reproducible Extraction of Local and Global Parameters for Functional Analysis of the Left Ventricle in 4D MR Image Data

Objectives: Left ventricle (LV) segmentation is required to quantify LV volume and mass parameters. Therefore, spatiotemporal Cine MR sequences in the short and long axis of the heart are acquired. Generally, LV segmentation methods consider short-axis sequences only. The reduced resolution in long-axis direction is one of the main reasons for inaccurate parameter extraction in the apical and basal area. The segmentation approach presented combines short- and long-axis information as well as motion tracking to enable the functional LV analysis in 4D MR Image Data.

Methods: First, anatomical landmarks like the mitral valve and the apex are defined in long-axis views in diastolic and systolic phase in order to specify the upper and lower boundary of the LV. Second, motion field approximation using non-linear registration enables the automatic contour propagation to all time points. Third, intersection planes are defined parallel to the mitral valve plane covering the whole ventricle. Finally, the 4D LV surface model is generated appending all in-plane contours. The segmentation results in short-axis images are checked and adjusted interactively and quantitative parameters are extracted.

Results: For evaluation the contours of 19 different datasets were traced by two medical experts using a contour drawing tool and the new segmentation tool. The results were compared to evaluate automatic contour propagation, robustness of the segmentation as well as interaction time.

Conclusion: The automatic contour propagation enables the fast and reproducible generation of a 4D model for the functional analysis of the heart. The interaction time is decreased from approx. 60 minutes to 10 minutes per case. Inter- and intraobserver differences of the extracted parameters are decreased significantly.

3D Segmentation of the Left Ventricle Combining Long- and Short-axis MR Images

Objectives: Segmentation of the left ventricle (LV) is required to quantify LV remodeling after myocardial infarction. Therefore spatiotemporal cine MR sequences including long-axis and short-axis images are acquired. In this paper a new segmentation method for fast and robust segmentation of the left ventricle is presented.

Methods: The new approach considers the position of the mitral valve and the apex as well as the long-axis contours to generate a 3D LV surface model. The segmentation result can be checked and adjusted in the short-axis images. Finally quantitative parameters were extracted.

Results: For evaluation the LV was segmented in eight datasets of the same subject by two medical experts using a contour drawing tool and the new segmentation tool. The results of both methods were compared concerning interaction time and intra- and inter-observer variance. The presented segmentation method proved to be fast. The mean difference and standard deviation of all parameters are decreased. In case of intra-observer comparison e.g. the mean ESV difference is reduced from 8.8% to 0.5%.

Conclusion: A semi-automatic LV segmentation method has been developed that combines long- and short-axis views. Using the presented approach the intra- and inter-observer difference as well as the time for the segmentation process are decreased. So the semi-automatic segmentation using long-and short-axis information proved to be fast and robust for the quantification of LV mass and volume properties.

Conserved Senescence Associated Genes and Pathways in Primary Human Fibroblasts Detected by RNA-Seq

Cellular senescence correlates with changes in the transcriptome. To obtain a complete view on senescence-associated transcription networks and pathways, we assessed by deep RNA sequencing the transcriptomes of five of the most commonly used laboratory strains of human fibroblasts during their transition into senescence. In a number of cases, we verified the RNA-seq data by real-time PCR. By determining cellular protein levels we observed that the age-related expression of most but not all genes is regulated at the transcriptional level. We found that 78% of the age-affected differentially expressed genes were commonly regulated in the same direction (either up- or down-regulated) in all five fibroblast strains, indicating a strong conservation of age-associated changes in the transcriptome. KEGG pathway analyses confirmed up-regulation of the senescence-associated secretory phenotype and down-regulation of DNA synthesis/repair and most cell cycle pathways common in all five cell strains. Newly identified senescence-induced pathways include up-regulation of endocytotic/phagocytic pathways and down-regulation of the mRNA metabolism and the mRNA splicing pathways. Our results provide an unprecedented comprehensive and deep view into the individual and common transcriptome and pathway changes during the transition into of senescence of five human fibroblast cell strains.

Experimental Validation of a Filament Transport Model in Turbulent Magnetized Plasmas

In a wide variety of natural and laboratory magnetized plasmas, filaments appear as a result of interchange instability. These convective structures substantially enhance transport in the direction perpendicular to the magnetic field. According to filament models, their propagation may follow different regimes depending on the parallel closure of charge conservation. This is of paramount importance in magnetic fusion plasmas, as high collisionality in the scrape-off layer may trigger a regime transition leading to strongly enhanced perpendicular particle fluxes. This work reports for the first time on an experimental verification of this process, linking enhanced transport with a regime transition as predicted by models. Based on these results, a novel scaling for global perpendicular particle transport in reactor relevant tokamaks such as ASDEX-Upgrade and JET is found, leading to important implications for next generation fusion devices.

Thoracic Pathologies on Scout Views and Bolus Tracking Slices for Computed Tomographic Cerebral Angiography

PURPOSE

To evaluate the incidence of additional thoracic pathologic findings (TPF) detected on scout views and corresponding bolus tracking slices (SVBT) for computed tomographic cerebral angiography (CTCA) and to test the reliability and accuracy of these findings.

MATERIALS AND METHODS

The study collective included 505 consecutive patients who underwent multidetector CTCA. Appendant SVBT of all patients were reviewed for any pathologic findings and patient medical reports were analyzed, if any medical treatment was initiated for the detected pathologic findings. In 18 patients thoracic CT scans were performed in the same session. These were additionally reviewed by two blinded observers to test for intra- and interobserver reliability as well as for accuracy of detecting thoracic pathologies on SVBT.

RESULTS

TPF were detected in 165 (33%) SVBT. The five most common pathologic findings were: pleural effusion, 12%; pneumonia, 8%; atelectasis/dystelecatsis, 6%; pericardial effusion, 2% and elevated diaphragm, 1%. For 48 % of these findings medical treatment was initiated. SVBT showed a sensitivity of 53%, a specificity of 99%, a positive predictive value of 89%, a negative predictive value of 94% and accuracy of 94% for the detection of TPF. The intraobserver reliability was very good and the interobserver reliability showed moderate agreement.

CONCLUSION

SVBT for CTCA should be reviewed with care by radiologists, since additional TPF can affect patient management. Nevertheless, despite a high specificity of SVBT for detecting TPF, an only moderate sensitivity has to be taken into account.

KEY POINTS

Thoracic pathologies are frequently found on scout views for cerebral CTA. Reviewing additional bolus trigger slices will improve diagnostic sensitivity. Despite high specificity, scout views and trigger slices offer a moderate sensitivity. Evaluation of scout views and trigger slices can result in medical treatment.

Significance of clinical examination, CT and MRI scan in the diagnosis of posterior pelvic ring fractures

INTRODUCTION

Patients with a fracture in the anterior pelvic ring often simultaneously demonstrate pain in the posterior pelvic ring. The aim of the present prospective study was to assess the sensitivity of CT, MRI and clinical examination in the detection of fractures in the posterior pelvic ring in patients with fractures of the anterior pelvic ring diagnosed in conventional radiographs.

METHODS

Sixty patients with radiographic signs of an anterior pelvic ring injury were included in this prospective analysis. Following a focused clinical examination of the posterior pelvis, all patients underwent both a CT and then a MRI scan of their pelvis. Two board certified radiologists evaluated the CT and MRI scans independently. To estimate the presence of osteoporosis the Hounsfield units of the vertebral body of L5 were measured in each case.

RESULTS

Fifty-three women and seven men, with a mean age of 74.7+/-15.6 years were included into the study. A fracture of the posterior pelvic ring was found in fourty-eight patients (80%) patients using MRI. Fractures of the posterior pelvic ring would have been missed in eight cases (17%), if only CT had been used. Eighty-five percent of the patients with a posterior fracture had an osteoporosis. The majority of the cases suffered from a low energy trauma. Thirty-eight patients (83%) with positive clinical signs at the posterior pelvic ring actually had a fracture of the posterior pelvic ring in the MRI. The clinical examination proved to be equally effective to CT in detecting posterior pelvic ring fractures.

CONCLUSION

The significance of both, clinical examination and CT was confirmed in the detection of fractures in the posterior pelvic ring. MRI examination of the pelvis however, was found to be superior in detecting undislocated fractures in a cohort of patients with a high incidence of osteoporosis. Using MRI may be beneficial in select cases, especially when reduced bone density is suspected.

Sensitivity of visual and quantitative detection of middle cerebral artery occlusion on non-contrast-enhanced computed tomography

INTRODUCTION

This study aims to investigate diagnostic sensitivity and reliability for the detection of middle cerebral artery occlusion (MCAO) on non-contrast-enhanced computed tomography (NECT) by visual assessment (VA), Hounsfield unit (HU) measurement, calculation of the Hounsfield unit/hematocrit (HU/Hct) ratio, and combination of visual assessment and attenuation measurement (VA + HU).

METHODS

NECT of 18 patients with angiographically proven MCAO and 18 patients without MCAO were reviewed by two blinded observers. Visual assessment of presence or absence of a hyperdense sign was followed by HU measurement of both middle cerebral arteries (MCA). Sensitivity, specificity, positive predictive value, and negative predictive value were calculated for VA, HU measurement, HU/Hct ratio, and VA + HU measurement. Receiver operating characteristic curve analysis (ROC) was performed to determine the optimal cut-off values for MCAO using attenuation measurements or HU/Hct ratio.

RESULTS

Diagnostic sensitivity/specificity was 63%/91% for VA, 56%/88% for attenuation measurement, 68 %/81 % for HU/Hct ratio, and 75%/78% for VA + HU. ROC curve analysis revealed cut-off values of >42.5 HU for attenuation measurements and >1.12 HU/Hct for HU/Hct ratio.

CONCLUSION

Combination of visual assessment with additional attenuation measurement with a cut-off value of 42.5 HU is recommended for most sensitive and reliable detection of MCAO on NECT.

Aneurysm Recurrence Volumetry Is More Sensitive than Visual Evaluation of Aneurysm Recurrences

PURPOSE

Considerable inter-observer variability in the visual assessment of aneurysm recurrences limits its use as an outcome parameter evaluating new coil generations. The purpose of this study was to compare visual assessment of aneurysm recurrences and aneurysm recurrence volumetry with an example dataset of HydroSoft coils (HSC) versus bare platinum coils (BPC).

METHODS

For this retrospective study, 3-dimensional time-of-flight magnetic resonance angiography datasets acquired 6 and 12 months after endovascular therapy using BPC only or mainly HSC were analyzed. Aneurysm recurrence volumes were visually rated by two observersas well as quantified by subtraction of the datasets after intensity-based rigid registration.

RESULTS

A total of 297 aneurysms were analyzed (BPC: 169, HSC: 128). Recurrences were detected by aneurysm recurrence volumetry in 9 of 128 (7.0 %) treated with HSC and in 24 of 169 (14.2 %) treated with BPC (odds ratio: 2.39, 95 % confidence interval: 1.05-5.48; P = 0.039). Aneurysm recurrence volumetry revealed an excellent correlation between observers (Cronbach's alpha = 0.93). In contrast, no significant difference in aneurysm recurrence was found for visual assessment (3.9 % in HSC cases and 4.7 % in BPC cases). Recurrences were observed in aneurysms smaller than the sample median in 10 of 33 (30.3 %) by aneurysm recurrence volumetry and in 1 of 13 (7.7 %) by visual assessment.

CONCLUSIONS

Aneurysm recurrences were detected more frequently by aneurysm recurrence volumetry when compared with visual assessment. By using aneurysm recurrence volumetry, differences between treatment groups were detected with higher sensitivity and inter-observer validity probably because of the higher detection rate of recurrences in small aneurysms.

Application of a novel metal artifact correction algorithm in flat-panel CT after coil embolization of brain aneurysms: intraindividual comparison

PURPOSE

To evaluate a novel algorithm for correcting beam hardening artifacts caused by metal implants in computed tomography performed on a C-arm angiography system equipped with a flat panel (FP-CT).

MATERIALS AND METHODS

16 datasets of cerebral FP-CT acquisitions after coil embolization of brain aneurysms in the context of acute subarachnoid hemorrhage have been reconstructed by applying a soft tissue kernel with and without a novel reconstruction filter for metal artifact correction. Image reading was performed in multiplanar reformations (MPR) in average mode on a dedicated radiological workplace in comparison to the preinterventional native multisection CT (MS-CT) scan serving as the anatomic gold standard. Two independent radiologists performed image scoring following a defined scale in direct comparison of the image data with and without artifact correction. For statistical analysis, a random intercept model was calculated.

RESULTS

The inter-rater agreement was very high (ICC = 86.3 %). The soft tissue image quality and visualization of the CSF spaces at the level of the implants was substantially improved. The additional metal artifact correction algorithm did not induce impairment of the subjective image quality in any other brain regions.

CONCLUSION

Adding metal artifact correction to FP-CT in an acute postinterventional setting helps to visualize the close vicinity of the aneurysm at a generally consistent image quality.