3D Wall Research Articles

Improved dynamic response of magnetic feedback in RFX-mod and DIII-D

The wall of any magnetic fusion device is characterized by the presence of several 3D structures, such as portholes for diagnostics and for heating and current drive systems, coil feeds and other features. Time-varying magnetic fields induce eddy currents in the wall, whose pattern is modified by these structures, giving rise to magnetic field errors that can be amplified or shielded by the plasma. Two examples will be given on how the dynamic response of a 3D wall to external magnetic fields can be identified and used to optimize magnetic feedback. In the RFX-mod reversed-field pinch, a dynamic decoupler algorithm has been developed, which allows for the production of pure radial magnetic field harmonics inside the wall, reducing the harmonic distortion due to the 3D wall structures. This is applied here to the problem of producing helical boundary conditions to control helical RFP equilibria. In the DIII-D tokamak, a frequency-dependent scheme for the compensation of the magnetic sensors from spurious n = 1 fields due to the coupling with the feedback and axisymmetric coils has been recently implemented in real time and tested with plasma. The possible relevance of these 3D effects for high performance scenarios is discussed.

Dynamic decoupling and multi-mode magnetic feedback for error field correction in RFX-mod

Magnetic field errors can have a significant impact on the confinement properties of magnetized fusion plasmas. In the RFX-mod reversed-field pinch (Sonato et al 2003 Fusion Eng. Des. 33 161) a significant error field is produced during the current ramp by the eddy currents induced in the 3D wall structures, such as the gaps and some large portholes, by the temporal variation of the vertical magnetic field. A set of 192 magnetic sensors and 192 active coils allowed accurate identification of the error field spatiotemporal pattern and its correction. The correction scheme combines pre-programmed current waveforms and multi-mode magnetic feedback. The pre-programmed currents were computed with the dynamic decoupling algorithm developed in Soppelsa et al (2008 Fusion Eng. Des. 83 224). This accounts for the mutual interaction between different feedback coils and magnetic sensors, which is affected by the frequency-dependent response of the 3D wall structures to external magnetic fields. At the same time, multi-mode magnetic feedback is applied to the main error field harmonics. During the current ramp, multiple tearing modes are normally phase-locked and produce a toroidally localized deformation of the plasma column that tends to grow where the error fields are larger. With error field correction, this deformation does not grow at preferred positions, thus avoiding the plasma–wall interaction being too localized there. In general, the decoupling approach used in this work may find applications in other machines.

Computational fluid dynamic simulations of aortic coarctation comparing the effects of surgical‐ and stent‐based treatments on aortic compliance and ventricular workload

In this work, we examine the effects of stent-induced aortic stiffness on cardiac workload and blood pressure using computational fluid dynamic simulations. Treatment of aortic coarctation (CoA) consists of either open, surgical repair or angioplasty with or without stenting. Although stenting is a minimally invasive alternative to surgery, aortic stiffness increases in the stented section. Concern over this increased stiffness has long been argued to be detrimental to the overall vascular health of the patient. MR imaging was performed on a 15-year-old female with CoA. A 3D model of the large thoracic arteries was created, and the heart and downstream vasculature were represented by lumped parameter models at the model inlet and outlets, respectively. A deformable wall assumption was used in conjunction with variable wall properties and tissue support, and 3D velocity, pressure, and wall dynamics were computed. The lumped parameter values and wall properties were tuned to match the mean flow and aortic deformation as measured by MRI. The CoA was then virtually removed from the model representing an end-to-end surgical correction. In a second model, the repaired section was prescribed to be nearly rigid, representing stenting. All other variables remained the same. When compared to surgery, stenting resulted in clinically negligible increases in cardiac work (0.4%) and no change in mean blood pressure. This pilot study suggests CoA stenting may not affect cardiac work to any significant degree as is commonly believed in the clinical community.

Dynamic estimation of three‐dimensional cerebrovascular deformation from rotational angiography

The objective of this study is to investigate the feasibility of detecting and quantifying 3D cerebrovascular wall motion from a single 3D rotational x-ray angiography (3DRA) acquisition within a clinically acceptable time and computing from the estimated motion field for the further biomechanical modeling of the cerebrovascular wall. The whole motion cycle of the cerebral vasculature is modeled using a 4D B-spline transformation, which is estimated from a 4D to 2D + t image registration framework. The registration is performed by optimizing a single similarity metric between the entire 2D + t measured projection sequence and the corresponding forward projections of the deformed volume at their exact time instants. The joint use of two acceleration strategies, together with their implementation on graphics processing units, is also proposed so as to reach computation times close to clinical requirements. For further characterizing vessel wall properties, an approximation of the wall thickness changes is obtained through a strain calculation. Evaluation on in silico and in vitro pulsating phantom aneurysms demonstrated an accurate estimation of wall motion curves. In general, the error was below 10% of the maximum pulsation, even in the situation when substantial inhomogeneous intensity pattern was present. Experiments on in vivo data provided realistic aneurysm and vessel wall motion estimates, whereas in regions where motion was neither visible nor anatomically possible, no motion was detected. The use of the acceleration strategies enabled completing the estimation process for one entire cycle in 5-10 min without degrading the overall performance. The strain map extracted from our motion estimation provided a realistic deformation measure of the vessel wall. The authors' technique has demonstrated that it can provide accurate and robust 4D estimates of cerebrovascular wall motion within a clinically acceptable time, although it has to be applied to a larger patient population prior to possible wide application to routine endovascular procedures. In particular, for the first time, this feasibility study has shown that in vivo cerebrovascular motion can be obtained intraprocedurally from a 3DRA acquisition. Results have also shown the potential of performing strain analysis using this imaging modality, thus making possible for the future modeling of biomechanical properties of the vascular wall.

Simultaneous 3D left and right coronary artery vessel wall imaging

Background Vessel wall imaging is commonly gated to alternate R-waves, in order to increase SNR and minimise artefacts due to RR-interval variation. In previous work with 2D carotid artery wall imaging, the resulting redundant RR-interval has been used to acquire additional parallel slices[1]. We postulate that the redundant RR-interval can be used to image an additional volume in 3D coronary artery wall imaging. In conjunction with highly efficient beat-to-beat respiratory motion correction (B2B-RMC)[2], this could allow high resolution 3D acquisitions of both the left and right coronary walls in ~10minutes.

MRI detects coronary vessel wall thickening with age in healthy subjects

Background Autopsy studies [1,2] and x-ray CT in older subjects with suspected disease [3] have demonstrated increasing coronary vessel thickness with age. There is, however, a need for a radiation-free non-invasive technique for use in longitudinal studies of coronary vessel wall morphology. Recently 3D MR coronary vessel wall imaging with retrospective beat-to-beat respiratorymotion-correction (B2B-RMC)[4], which uses 3D low resolution data acquired immediately before the main imaging data to retrospectively correct respiratory motion, has demonstrated great promise [5]. We propose that 3D high resolution MR with B2B-RMC can demonstrate coronary vessel wall thickening with age in healthy subjects.

Reproducibility of coronary vessel wall imaging techniques

Background Coronary wall thickness measurements must be highly reproducible to be useful in longitudinal studies. While 2D turbo-spin-echo (TSE) and spiral techniques are commonly used, 3D techniques reduce partial-volume effects and allow greater vessel coverage. Recently, 3D coronary wall imaging was demonstrated with 100% respiratory efficiency (RE) using beat-to-beat respiratory motion correction (B2B-RMC) [1] which uses motion information determined from low resolution 3D images of the fat around the vessel as a surrogate for vessel motion. Here we assess the reproducibility of this technique together with that of navigator-gated 2D TSE and spiral acquisitions. Methods Cross-sectional right coronary artery wall images were obtained in 10 healthy subjects on a Siemens 1.5T Avanto scanner using dark-blood prepared B2B-RMC 3D spiral imaging, navigator-gated 2D TSE imaging and navigator-gated 2D spiral imaging. Acquisition order was randomized and subjects were imaged on two separate occasions to assess inter-study reproducibility using the intra-class correlation-coefficient (ICC) and Bland Altman analysis. All acquisitions used 0.7x0.7mm inplane resolution. B2B-RMC 3D spiral acquisitions acquired 8x3.0mm slices (16x1.5mm reconstructed) and 2D techniques acquired 1x6mm slice. Navigator-gated techniques used a 5mm window while B2B-RMC excluded data acquired at only very extreme respiratory positions, retrospectively correcting the rest. Durations, assuming 100% RE, were 600 cardiac cycles (CC) for B2B-RMC, 75CC for 2D spiral and 202-576CC for 2D

The 3d left ventricular geometry integrated in myocardial wall stress estimation is more sensitive than end diastolic mass/volume ratio to characterize afterload-related left ventricular remodeling

To maintain an effective LV-arterial coupling the LV adapts to the increased afterload caused by aging or cardiovascular disease. However, subsequent changes in LV mass and concentric remodeling have been associated with poor outcome. To understand LV remodeling, we studied variations of 3D myocardial wall stress (MWS), its geometrical factor as well as diastolic LV mass to volume ratio (LVM/EDV) on a population with a wide range of afterload.

High‐resolution 3D coronary vessel wall imaging with near 100% respiratory efficiency using epicardial fat tracking: Reproducibility and comparison with standard methods

To quantitatively assess the performance and reproducibility of 3D spiral coronary artery wall imaging with beat-to-beat respiratory-motion-correction (B2B-RMC) compared to navigator gated 2D spiral and turbo-spin-echo (TSE) acquisitions. High-resolution (0.7 × 0.7 mm) cross-sectional right coronary wall acquisitions were performed in 10 subjects using four techniques (B2B-RMC 3D spiral with alternate (2RR) and single (1RR) R-wave gating, navigator-gated 2D spiral (2RR) and navigator-gated 2D TSE (2RR)) on two occasions. Wall thickness measurements were compared with repeated measures analysis of variance (ANOVA). Reproducibility was assessed with the intraclass correlation coefficient (ICC). In all, 91% (73/80) of acquisitions were successful (failures: four TSE, two 3D spiral (1RR) and one 3D spiral (2RR)). Respiratory efficiency of the B2B-RMC was less variable and substantially higher than for navigator gating (99.6 ± 1.2% vs. 39.0 ± 7.5%, P < 0.0001). Coronary wall thicknesses (± standard deviation [SD]) were not significantly different: 1.10 ± 0.14 mm (3D spiral (2RR)), 1.20 ± 0.16 mm (3D spiral (1RR)), 1.14 ± 0.15 mm (2D spiral), and 1.21 ± 0.17 mm (TSE). Wall thickness reproducibility ranged from good (ICC = 0.65, 3D spiral (1RR)) to excellent (ICC = 0.87, 3D spiral (2RR)). High-resolution 3D spiral imaging with B2B-RMC permits coronary vessel wall assessment over multiple thin contiguous slices in a clinically feasible duration. Excellent reproducibility of the technique potentially enables studies of disease progression/regression.

Incidental Radiation Dose to Presumed Uninvolved Internal Mammary Lymph Nodes in Breast Cancer Patients Receiving Post-mastectomy Irradiation Adjuvant Therapy

Routine prophylactic treatment of uninvolved internal mammary nodes (IMN) in breast cancer patients requiring post-mastectomy radiation therapy (PMRT) is controversial. While randomized trials demonstrating survival benefit of PMRT often included IMNs, doing so increases the normal tissue doses, especially the heart dose, which is associated with an increase in radiation induced morbidity/mortality. The purpose of this study was to measure the incidental radiation dose to the internal mammary lymph nodes (IMN) not included in the planning target volume (PTV) in women with breast cancer receiving PMRT irradiation. This study was a retrospective, IRB approved protocol using CT-based 3D conformal (3D CRT) treatment plans. Thirty-three consecutive patients were included in the analysis: 17 left side and 16 right side patients. All patients received standard 3D CRT chest wall tangent fields and matched supraclavicular (SCV) fields. All plans were prescribed a total dose of 50 Gy in 25 fractions to the chest wall and 46 Gy in 23 fractions to the SCV field. The IMN chain was not intentionally included in the target volume. For purposes of this study, IMN vessels were contoured following the RTOG atlas, utilizing original CT simulation images. A 7 mm PTV expansion was added to the IMN contours. Pinnacle treatment planning algorithm was used to quantify the radiation dose volume histograms. The percent volume of IMN PTV receiving 100% of the prescribed dose (50Gy) for all patients was 24% (range, 0-73%, SD 23.9). The percent volume of IMN PTV receiving 95% of the prescribed dose (45 Gy) for all patients was 34% (range, 0.6-92%, SD 27.3). The percent volume of IMN PTV receiving 90% of the prescribed dose (40 Gy) for all patients was 39.5% (range, 1-97%, SD 28.8). The mean IMN dose for all patients was 23.4 Gy (range, 3.5-52.9, SD 15.8). The IMN absolute dose range for all patients was 5.09- 51.05 Gy. The volume of lung receiving 20 Gy (V20) for left sided and right sided were 13.8%, (range, 7.23-18.5%, SD 2.8%) and 15.5% (range, 8.9-28.4%, SD 5.1%), respectively. The volume of heart receiving 30 Gy (V30) for left sided and right sided were 4.2% (range, 0.05-13.3%, SD 3.8%) and 0.0003% (range, 0-0.4%, SD 0.001%) respectively. The results of this study suggest that the incidental dose to the IMN nodes does not achieve therapeutic levels in post mastectomy breast cancer patients treated with standard 3D CRT chest wall irradiation. If risk factors for microscopic involvement are present, IMNs must be specifically included in target volumes in order to be adequately treated.

Mechanical left ventricular dyssynchrony detection by endocardium displacement analysis with 3D speckle tracking technology

Myocardium deformation and displacement analysis by echocardiography has proven useful to evaluate the synchrony of myocardial mechanics. The aim of our study was to evaluate the mean standard deviation of time to longitudinal peak displacement in 16 cardiac segments by 3D echo wall motion Speckle Tracking analysis. We studied 15 patients with ventricular dyssynchrony-defined by a QRS > 120 ms in the ECG. We obtained the differences between time peaks of endocardial longitudinal displacement for 16 segments of the heart by 3D echo Speckle Tracking. We compared the temporal dispersion of these peaks with results obtained in a control group of 13 healthy individuals without dyssynchrony. The results showed a significant difference (p < 0.001) between the dispersion of standard deviation in the 13 patients in the control group (34 ms ± 19) and the 15 patients in the dyssynchrony group (117 ms ± 57). We describe a new parameter obtained by 3D echo wall motion Speckle Tracking analysis for the detection of dyssynchrony. It can be useful to identify dyssynchrony of left ventricular myocardial mechanics, to indicate the resynchronization therapy, to optimize the parameters of the device and to achieve a less operator-dependent evaluation.

3D flow-independent peripheral vessel wall imaging using T(2)-prepared phase-sensitive inversion-recovery steady-state free precession.

To develop a 3D flow-independent peripheral vessel wall imaging method using T(2)-prepared phase-sensitive inversion-recovery (T(2)PSIR) steady-state free precession (SSFP). A 3D T(2)-prepared and nonselective inversion-recovery SSFP sequence was designed to achieve flow-independent blood suppression for vessel wall imaging based on T(1) and T(2) properties of the vessel wall and blood. To maximize image contrast and reduce its dependence on the inversion time (TI), phase-sensitive reconstruction was used to restore the true signal difference between vessel wall and blood. The feasibility of this technique for peripheral artery wall imaging was tested in 13 healthy subjects. Image signal-to-noise ratio (SNR), wall/lumen contrast-to-noise ratio (CNR), and scan efficiency were compared between this technique and conventional 2D double inversion recovery - turbo spin echo (DIR-TSE) in eight subjects. 3D T(2)PSIR SSFP provided more efficient data acquisition (32 slices and 64 mm in 4 minutes, 7.5 seconds per slice) than 2D DIR-TSE (2-3 minutes per slice). SNR of the vessel wall and CNR between vessel wall and lumen were significantly increased as compared to those of DIR-TSE (P < 0.001). Vessel wall and lumen areas of the two techniques are strongly correlated (intraclass correlation coefficients: 0.975 and 0.937, respectively; P < 0.001 for both). The lumen area of T(2)PSIR SSFP is slightly larger than that of DIR-TSE (P = 0.008). The difference in vessel wall area between the two techniques is not statistically significant. T(2)PSIR SSFP is a promising technique for peripheral vessel wall imaging. It provides excellent blood signal suppression and vessel wall/lumen contrast. It can cover a 3D volume efficiently and is flow- and TI-independent.

Assessment of left ventricular function by different speckle-tracking software

Two-dimensional (2D) speckle echocardiography enables objective assessment of left ventricular function through the analysis of myocardial strain, which can be measured by different speckle-tracking software. The aim of this study was to compare two different commercially available cardiac ultrasound systems and their manufacturer-specific speckle-tacking software for the quantification of global myocardial strain in a healthy population. Twenty-eight healthy subjects (age: 38 +/- 12, 64% males) underwent two 2D echocardiograms within the same day using different cardiac ultrasound systems: Vivid 7 (GE Ultrasound, Horten, Norway) and Artida 4D (Toshiba Medical Systems). Standard apical and short-axis views of the left ventricle were obtained in each subject with a frame-rate range of 60 +/- 20 frames/s. Global longitudinal, radial, and circumferential strain values were analysed using their respective speckle-tracking software for Vivid (2D-strain EchoPac PC v.7.0.1, GE Healthcare, Horten, Norway) and Toshiba systems (2D Wall Motion Tracking, Toshiba Medical Systems). Global strain values were estimated from the average of regional left ventricular strain values. Agreement between the two systems and software was assessed by Bland-Altman method. Mean left ventricular ejection fraction was 59 +/- 7%. Global longitudinal, radial, and circumferential strain values were, respectively, -21.95 +/- 1.8, 46.97 +/- 5.5, and -23.18 +/- 3.3% when using 2D-strain EchoPac and -22.28 +/- 2.1, 40.74 +/- 4.3, and -27.17 +/- 4.7% when 2D Wall Motion Tracking was used (P = NS). Limits of agreement between both speckle-tracking software were narrower for global longitudinal strain (-2.25 to 3.65) than for radial and circumferential strain (-2.23 to 12.44 and -1.36 to 10.54, respectively). Two commercially available speckle-tracking software appear to be comparable when quantifying left ventricular function in a healthy population. Global longitudinal strain is a more robust parameter than radial and circumferential strain for the assessment of myocardial function when different cardiac ultrasound systems are used for analysis.

3D Critical Plaque Wall Stress Is a Better Predictor of Carotid Plaque Rupture Sites Than Flow Shear Stress: An In Vivo MRI-Based 3D FSI Study

Atherosclerotic plaque rupture leading to stroke is the major cause of long-term disability as well as the third most common cause of mortality. Image-based computational models have been introduced seeking critical mechanical indicators, which may be used for plaque vulnerability assessment. This study extends the previous 2D critical stress concept to 3D by using in vivo magnetic resonance image (MRI) data of human atherosclerotic carotid plaques and 3D fluid-structure interaction (FSI) models to: identify 3D critical plaque wall stress (CPWS) and critical flow shear stress (CFSS) and to investigate their associations with plaque rupture. In vivo MRI data of carotid plaques from 18 patients scheduled for endarterectomy were acquired using histologically validated multicontrast protocols. Of the 18 plaques, histology-confirmed that six had prior rupture (group 1) as evidenced by presence of ulceration. The remaining 12 plaques (group 2) contained no rupture. The 3D multicomponent FSI models were constructed for each plaque to obtain 3D plaque wall stress (PWS) and flow shear stress (FSS) distributions. Three-dimensional CPWS and CFSS, defined as maxima of PWS and FSS from all vulnerable sites, were determined for each plaque to investigate their association with plaque rupture. Slice-based critical PWS and FSS were also calculated for all slices for more detailed analysis and comparison. The mean 3D CPWS of group 1 was 263.44 kPa, which was 100% higher than that from group 2 (132.77, p=0.03984). Five of the six ruptured plaques had 3D CPWS sites, matching the histology-confirmed rupture sites with an 83% agreement. Although the mean 3D CFSS (92.94 dyn/cm(2)) for group 1 was 76% higher than that for group 2 (52.70 dyn/cm(2)), slice-based CFSS showed no significant difference between the two groups. Only two of the six ruptured plaques had 3D CFSS sites matching the histology-confirmed rupture sites with a 33% agreement. CFSS had a good correlation with plaque stenosis severity (R(2)=0.40 with an exponential function fitting 3D CFSS data). This in vivo MRI pilot study using plaques with and without rupture demonstrates that 3D critical plaque wall stress values are more closely associated with atherosclerotic plaque rupture then critical flow shear stresses. Critical wall stress values may become indicators of high risk sites of rupture. Future work with a larger population will establish a possible CPWS-based plaque vulnerability classification.

Quantification of 3D regional myocardial wall thickening from gated magnetic resonance images

To develop 3D quantitative measures of regional myocardial wall motion and thickening using cardiac magnetic resonance imaging (MRI) and to validate them by comparison to standard visual scoring assessment. In all, 53 consecutive subjects with short-axis slices and mid-ventricular 2-chamber/4-chamber views were analyzed. After correction for breath-hold-related misregistration, 3D myocardial boundaries were fitted to images and edited by an imaging cardiologist. Myocardial thickness was quantified at end-diastole and end-systole by computing the 3D distances using Laplace's equation. 3D thickening was represented using the standard 17-segment polar coordinates. 3D thickening was compared with 3D wall motion and with expert visual scores (6-point visual scoring of wall motion and wall thickening; 0 = normal; 5 = greatest abnormality) assigned by imaging cardiologists. Correlation between ejection fraction and thickening measurements was (r = 0.84; P < 0.001) compared to correlation between ejection fraction and motion measurements (r = 0.86; P < 0.001). Good negative correlation between summed visual scores and global wall thickening and motion measurements were also obtained (r(thick) = -0.79; r(motion) = -0.74). Additionally, overall good correlation between individual segmental visual scores with thickening/wall motion (r(thick) = -0.69; r(motion) = -0.65) was observed (P < 0.0001). 3D quantitative regional thickening and wall motion measures obtained from MRI correlate strongly with expert clinical scoring.

3D flow-insensitive vessel wall imaging using T2-prepared SSFP with PSIR

Introduction Double Inversion Recovery (DIR) [1] and Flow Sensitive Diffusion (FSD)[2] have been used to in vessel wall imaging. However, the black blood effect of DIR and FSD depends on the inflow, which is sensitive to slow or inplane flow. In this work, T1, T2 difference between blood/ vessel wall was exploited using a T2-prepared non-selective inversion preparation for flow-insensitive vessel wall imaging. To alleviate the dependence of blood/vessel wall contrast on the choice of TI and heart rate in ECG-triggered data acquisition, a Phase Sensitive Inversion Recovery (PSIR) [3] approach was used.

3D fusion of intravascular ultrasound and coronary computed tomography for in-vivo wall shear stress analysis: a feasibility study

Wall shear stress, the force per area acting on the lumen wall due to the blood flow, is an important biomechanical parameter in the localization and progression of atherosclerosis. To calculate shear stress and relate it to atherosclerosis, a 3D description of the lumen and vessel wall is required. We present a framework to obtain the 3D reconstruction of human coronary arteries by the fusion of intravascular ultrasound (IVUS) and coronary computed tomography angiography (CT). We imaged 23 patients with IVUS and CT. The images from both modalities were registered for 35 arteries, using bifurcations as landmarks. The IVUS images together with IVUS derived lumen and wall contours were positioned on the 3D centerline, which was derived from CT. The resulting 3D lumen and wall contours were transformed to a surface for calculation of shear stress and plaque thickness. We applied variations in selection of landmarks and investigated whether these variations influenced the relation between shear stress and plaque thickness. Fusion was successfully achieved in 31 of the 35 arteries. The average length of the fused segments was 36.4±15.7mm. The length in IVUS and CT of the fused parts correlated excellently (R (2)=0.98). Both for a mildly diseased and a very diseased coronary artery, shear stress was calculated and related to plaque thickness. Variations in the selection of the landmarks for these two arteries did not affect the relationship between shear stress and plaque thickness. This new framework can therefore successfully be applied for shear stress analysis in human coronary arteries.

ASCOT simulations of fast ion power loads to the plasma-facing components in ITER

The wall loads due to fusion alphas as well as neutral beam injection- and ICRF-generated fast ions were simulated for ITER reference scenario-2 and scenario-4 including the effects of ferritic inserts (FIs), test blanket modules (TBMs), and 3D wall with two limiter structures. The simulations were carried out using the Monte Carlo guiding-centre orbit-following code ASCOT. The FIs were found very effective in ameliorating the detrimental effects of the toroidal ripple: the fast ion wall loads are reduced practically to their negligible axisymmetric level. The thermonuclear alpha particles overwhelmingly dominate the wall power flux. In scenario-4 practically all the power goes to the limiters, while in scenario-2 the load is fairly evenly divided between the divertor and the limiter, with hardly any power flux to other components in the first wall. This is opposite to earlier results, where hot spots were observed with 2D wall (Tobita et al 2003 Fusion Eng. Des. 65 561–8). In contrast, uncompensated ripple leads to unacceptable peak power fluxes of 0.5 MW m−2 in scenario-2 and 1 MW m−2 in scenario-4, with practically all power hitting the limiters and substantial flux arriving even at the unprotected first wall components. The local TBM structures were found to perturb the magnetic field structure globally and lead to increased wall loads. However, the TBM simulation results overestimate the TBM contribution due to an over-simplification in the vacuum field. Therefore the TBM results should be considered as an upper limit.

Three-Dimensional-Wall Motion Tracking: A New and Faster Tool for Myocardial Strain Assessment: Comparison With Two-Dimensional-Wall Motion Tracking

Two-dimensional (2D) wall motion-tracking echocardiography (WMT) is a useful method to measure myocardial strain, but it is very limited because acquisition and analysis are time consuming. Three-dimensional (3D) WMT is a new method that might improve diagnostic usefulness and reduce study times. The aims of this study were to compare results on 2D and 3D WMT and to compare the times for the acquisition and analysis of regional myocardial strain between the two methods. Measurements of the radial and longitudinal strain of every left ventricular (LV) segment and the time for acquisition and analysis were obtained using 3D and 2D WMT. Thirty patients were enrolled (mean age, 57.2 +/- 19.6 years; 60% men). Three-dimensional WMT provided complete radial and longitudinal LV strain information, similar to 2D WMT (P = NS), but it was less time consuming: the times for acquisition and analysis were 14.0 +/- 1.9 minutes with 2D WMT and 5.1 +/- 1.1 minutes with 3D WMT (P < .001). Furthermore, in the same analysis, a greater number of segments could be analyzed using 3D WMT (72.4%) compared with 2D WMT (52.0%). Three-dimensional WMT provides a faster, more complete, and similar analysis to assess LV longitudinal and radial strain compared with 2D WMT. Thus, 3D WMT is a potential clinical bedside tool for quantifying myocardial strain.

3D MHD VDE and disruptions simulations of tokamaks plasmas including some ITER scenarios

Tokamaks vertical displacement events (VDEs) and disruptions simulations in toroidal geometry by means of a single fluid visco-resistive magneto-hydro-dynamic (MHD) model are presented in this paper. The plasma model is completed with the presence of a 2D wall with finite resistivity which allows the study of the relatively slowly growing magnetic perturbation, the resistive wall mode (RWM), which is, in this paper, the main drive of the disruption evolution. Amplitudes and asymmetries of the halo currents pattern at the wall are also calculated and comparisons with tokamak experimental databases and predictions for ITER are given.