Velocity-encoded MRI Research Articles

Ventricular arterial coupling in patients with ischemia but no obstructive coronary artery disease: novel insight into heart failure progression

Abstract Background Ischemia with no obstructive coronary artery disease (INOCA) is prevalent in women and is associated with increased risk of developing heart failure with preserved ejection fraction (HFpEF). While the exact mechanism contributing to heart failure progression remains incompletely understood, we hypothesize that impaired ventricular-arterial coupling (VAC) plays a key role. Purpose To evaluate VAC across the INOCA-HFpEF continuum. Methods To accomplish our research objective, we leveraged cardiac magnetic resonance images from individuals with INOCA and HFpEF from the WISE Pre-HFpEF (NCT03876223) and WISE HFpEF (NCT02582021) studies, along with reference controls. Aortic pulse wave velocity (aPWV) was measured using velocity-encoded MRI, from the proximal ascending to distal descending aorta. Global longitudinal strain (GLS) was measured by feature tracking of horizontal and vertical long axis cine images. VAC was defined as the ratio between aPWV and GLS. To test for potential mediators, we assessed the relationship between VAC and age, risk factors, systolic blood pressure (SBP), diastolic blood pressure (DBP), myocardial perfusion reserve index (MPRI), LV end diastolic pressure (LVEDP), cardiac structure/function, and Kansas City Cardiomyopathy questionnaire (KCCQ). Results The baseline characteristics of the three study groups are described in the Table. Patients with INOCA had similar KCCQ scores as HFpEF patients, suggesting INOCA patients may have subclinical HFpEF. Consistent with our hypothesis, we observed a progressive impairment in VAC across the three groups (Controls vs INOCA vs HFpEF), being significantly worst in HFpEF(Figure). Importantly, VAC was inversely related with age, systolic/diastolic blood pressure, and LV mass index (R=-0.6, R=-0.4, R=-0.4, R=-0.3 respectively, all p <0.001). Conclusion The data herein support the hypothesis that VAC contributes to heart failure progression, with age, arterial blood pressure and LV mass being key determinants. That VAC was not yet significantly different between INOCA, and reference controls highlights an important opportunity for intervention to prevent heart failure progression.

A comparison of phase unwrapping methods in velocity-encoded MRI for aortic flows.

The phase of a MRI signal is used to encode the velocity of blood flow. Phase unwrapping artifacts may appear when aiming to improve the velocity-to-noise ratio (VNR) of the measured velocity field. This study aims to compare various unwrapping algorithms on ground-truth synthetic data generated using computational fluid dynamics (CFD) simulations. We compare four different phase unwrapping algorithms on two different synthetic datasets of four-dimensional flow MRI and 26 datasets of 2D PC-MRI acquisitions including the ascending and descending aorta. The synthetic datasets are constructed using CFD simulations of an aorta with a coarctation, with different levels of spatiotemporal resolutions and noise. The error of the unwrapped images was assessed by comparison against the ground truth velocity field in the synthetic data and dual-VENC reconstructions in the in vivo data. Using the unwrapping algorithms, we were able to remove aliased voxels in the data almost entirely, reducing the L2-error compared to the ground truth by 50%-80%. Results indicated that the best choice of algorithm depend on the spatiotemporal resolution and noise level of the dataset. Temporal unwrapping is most successful with a high temporal and low spatial resolution ( ms, mm), reducing the L2-error by 70%-85%, while Laplacian unwrapping performs better with a lower temporal or better spatial resolution ( ms, mm), especially for signal-to-noise ratio (SNR) 12 as opposed to SNR 15, with an error reduction of 55%-85% compared to the 50%-75% achieved by the Temporal method. The differences in performance between the methods are statistically significant. The temporal method and spatiotemporal Laplacian method provide the best results, with the spatiotemporal Laplacian being more robust. However, single- methods only situationally and not generally reach the performance of dual- unwrapping methods.

Optimization of 4D Flow MRI Spatial and Temporal Resolution for Examining Complex Hemodynamics in the Carotid Artery Bifurcation.

Three-dimensional, ECG-gated, time-resolved, three-directional, velocity-encoded phase-contrast MRI (4D flow MRI) has been applied extensively to measure blood velocity in great vessels but has been much less used in diseased carotid arteries. Carotid artery webs (CaW) are non-inflammatory intraluminal shelf-like projections into the internal carotid artery (ICA) bulb that are associated with complex flow and cryptogenic stroke. Optimize 4D flow MRI for measuring the velocity field of complex flow in the carotid artery bifurcation model that contains a CaW. A 3D printed phantom model created from computed tomography angiography (CTA) of a subject with CaW was placed in a pulsatile flow loop within the MRI scanner. 4D Flow MRI images of the phantom were acquired with five different spatial resolutions (0.50-2.00 mm3) and four different temporal resolutions (23-96ms) and compared to a computational fluid dynamics (CFD) solution of the flow field as a reference. We examined four planes perpendicular to the vessel centerline, one in the common carotid artery (CCA) and three in the internal carotid artery (ICA) where complex flow was expected. At these four planes pixel-by-pixel velocity values, flow, and time average wall shear stress (TAWSS) were compared between 4D flow MRI and CFD. An optimized 4D flow MRI protocol will provide a good correlation with CFD velocity and TAWSS values in areas of complex flow within a clinically feasible scan time (~ 10min). Spatial resolution affected the velocity values, time average flow, and TAWSS measurements. Qualitatively, a spatial resolution of 0.50 mm3 resulted in higher noise, while a lower spatial resolution of 1.50-2.00 mm3 did not adequately resolve the velocity profile. Isotropic spatial resolutions of 0.50-1.00 mm3 showed no significant difference in total flow compared to CFD. Pixel-by-pixel velocity correlation coefficients between 4D flow MRI and CFD were > 0.75 for 0.50-1.00 mm3 but were < 0.5 for 1.50 and 2.00 mm3. Regional TAWSS values determined from 4D flow MRI were generally lower than CFD and decreased at lower spatial resolutions (larger pixel sizes). TAWSS differences between 4D flow and CFD were not statistically significant at spatial resolutions of 0.50-1.00 mm3 but were different at 1.50 and 2.00 mm3. Differences in temporal resolution only affected the flow values when temporal resolution was > 48.4ms; temporal resolution did not affect TAWSS values. A spatial resolution of 0.74-1.00 mm3 and a temporal resolution of 23-48ms (1-2k-space segments) provides a 4D flow MRI protocol capable of imaging velocity and TAWSS in regions of complex flow within the carotid bifurcation at a clinically acceptable scan time.

Assessment of Beat-To-Beat Variability in Left Atrial Hemodynamics Using Real Time Phase Contrast MRI in Patients With Atrial Fibrillation.

Hemodynamic assessment of left atrial (LA) flow using phase contrast MRI provides insight into thromboembolic risk in atrial fibrillation (AF). However, conventional flow imaging techniques are averaged over many heartbeats. To evaluate beat-to-beat variability and LA hemodynamics in patients with AF using real time phase contrast (RTPC) MRI. Prospective. Thirty-five patients with history of AF (68 ± 10 years, nine female), 10 healthy controls (57 ± 19 years, four female). 5T, 2D RTPC with through-plane velocity-encoded gradient echo sequence and 4D flow MRI with three-directional velocity-encoded gradient echo sequence. RTPC was continuously acquired for a mid-LA slice in all subjects. 4D flow data were interpolated at the RTPC location and normally projected for comparison with RTPC. RR intervals extracted from RTPC were used to calculate heart rate variability (HRV=interquartile range over median × 100%). Patients were classified into low (<9.7%) and high (>9.7%) HRV groups. LA peak/mean velocity and stasis (%velocities < 5.8cm/sec) were calculated from segmented 2D images. Variability in RTPC flow metrics was quantified by coefficient of variation (CV) over all cycles. Pearson's correlation coefficient (r), Bland-Altman analysis, Kruskal-Wallis test. A P value < 0.05 was considered statistically significant. RTPC and 4D flow measurements were strongly/significantly correlated for all hemodynamic parameters (R2 =0.75-0.83) in controls. Twenty-four patients had low HRV (mean=4 ± 2%) and 11 patients had high HRV (27 ± 9%). In patients, increased HRV was significantly correlated with CV of peak velocity (r=0.67), mean velocity (r=0.51), and stasis (r=0.41). A stepwise decrease in peak/mean velocity and increase in stasis was observed when comparing controls vs. low HRV vs. high HRV groups. Mean velocity and stasis differences were significant for control vs. high HRV groups. RTPC may be suitable for assessing the impact of HRV on hemodynamics and provide insight for AF management in highly arrhythmic patients. 1 TECHNICAL EFFICACY: Stage 2.

Parameter estimation in fluid flow models from aliased velocity measurements

Parameter estimation in blood flow models from measured velocity data—as e.g. velocity-encoded MRI—is a key step for patient-specific hemodynamic analysis. However, velocity encoding suffers from competing noise and aliasing artifacts, which negatively impact the parameter estimation results. The aim of this work is to propose a new inverse problem formulation capable of tackling aliased and noisy velocity MRI measurements in parameter estimation in flows. The formulation is based on a modification of the quadratic cost function for velocity measurements. This allows for a correct parameter estimation when they have influence on the whole measurement domain, in spite of aliasing artifacts. The new inverse problem can be solved numerically using any standard solver, and we show how a popular sequential approach can be applied. Numerical results in an aortic flow show robust parameter estimation for velocity encoding ranges until 30% of the maximal velocity of the problem, while the standard inverse problem fails already for any encoding velocity smaller than the true one. Moreover, the parameter estimation results are even improved for reduced velocity encoding ranges when using the new cost function. The presented approach allows therefore for great flexibility in personalization of blood flows models from MRI data commonly encountered in the clinical context.

Comparison of Improved Unidirectional Dual Velocity-Encoding MRI Methods.

In phase-contrast (PC) MRI, several dual velocity encoding methods have been proposed to robustly increase velocity-to-noise ratio (VNR), including a standard dual-VENC (SDV), an optimal dual-VENC (ODV), and bi- and triconditional methods. To develop a correction method for the ODV approach and to perform a comparison between methods. Case-control study. Twenty-six volunteers. 1.5 T phase-contrast MRI with VENCs of 50, 75, and 150 cm/second. Since we acquired single-VENC protocols, we used the background phase from high-VENC (VENCH ) to reconstruct the low-VENC (VENCL ) phase. We implemented and compared the unwrapping methods for different noise levels and also developed a correction of the ODV method. Shapiro-Wilk's normality test, two-way analysis of variance with homogeneity of variances was performed using Levene's test, and the significance level was adjusted by Tukey's multiple post hoc analysis with Bonferroni (P< 0.05). Statistical analysis revealed no extreme outliers, normally distributed residuals, and homogeneous variances. We found statistically significant interaction between noise levels and the unwrapping methods. This implies that the number of non-unwrapped pixels increased with the noise level. We found that for β= VENCL /VENCH = 1/2, unwrapping methods were more robust to noise. The post hoc test showed a significant difference between the ODV corrected and the other methods, offering the best results regarding the number of unwrapped pixels. All methods performed similarly without noise, but the ODV corrected method was more robust to noise at the price of a higher computational time. 4 TECHNICAL EFFICACY STAGE: 1.

Velocity-Encoded Phase-Contrast MRI for Measuring Mesenteric Blood Flow in Patients With Newly Diagnosed Small-Bowel Crohn Disease.

BACKGROUND. Intestinal inflammation is associated with radiologic and histologic hyperemia. A paucity of studies have used MRI to measure mesenteric blood flow in patients with Crohn disease. OBJECTIVE. The purpose of this study was to evaluate the application of velocity-encoded phase-contrast MRI for measuring mesenteric blood flow in patients with newly diagnosed small-bowel Crohn disease. METHODS. This prospective study included 20 patients with ileal Crohn disease newly diagnosed between December 2018 and October 2021 (eight female participants, 12 male participants; median age, 14.0 years), and 15 healthy control participants (eight female participants, seven male participants; median age, 17.0 years). Patients with Crohn disease underwent investigational MRI and laboratory assessments at diagnosis and at 6 weeks and 6 months after initiating anti-tumor necrosis factor-α medical therapy; control participants underwent a single investigational MRI examination. All MRI examinations included a velocity-encoded phase-contrast acquisition, which was used to measure blood flow in the abdominal aorta, superior mesenteric artery (SMA), and superior mesenteric vein (SMV). Mann-Whitney U test was used to compare blood flow measurements (ratios of SMA and SMV blood flow to aorta blood flow [hereafter, SMA-to-aorta and SMV-to-aorta blood flow, respectively]) between groups; Friedman test was used to evaluate temporal changes in blood flow. Spearman correlation was used to assess relationships between blood flow measurements and laboratory markers of intestinal inflammation. Diagnostic performance was assessed by ROC analysis. RESULTS. At baseline, SMA-to-aorta blood flow in patients versus control participants was 0.44 versus 0.30 (p = .003), and SMV-to-aorta blood flow was 0.36 versus 0.21 (p = .002). At 6 weeks and 6 months, SMA-to-aorta blood flow in patients decreased to 0.30 and 0.27 (p < .001), and SMV-to-aorta blood flow decreased to 0.27 and 0.21 (p = .02), respectively. SMA-to-aorta and SMV-to-aorta blood flow were positively correlated with C-reactive protein (rho, 0.34 [p = .01] and 0.35 [p = .008], respectively) and fecal calprotectin (rho, 0.34 [p = .01] vs 0.47 [p < .001]). AUCs for differentiating patients from controls were 0.79 for SMA-to-aorta (sensitivity, 60%; specificity, 100%) and 0.82 for SMV-to-aorta (sensitivity, 75%; specificity, 87%) blood flow. CONCLUSION. Mesenteric blood flow is quantifiable using velocity-encoded phase-contrast MRI. The measurements differ between patients with ileal Crohn disease and healthy control participants and change in response to medical therapy. CLINICAL IMPACT. MRI-based mesenteric blood flow measurements provide a potential novel marker of intestinal inflammation.

Dynamics of Quadriceps Muscles during Isometric Contractions: Velocity-Encoded Phase Contrast MRI Study.

Objective: To quantify the spatial heterogeneity of displacement during voluntary isometric contraction within and between the different compartments of the quadriceps. Methods: The thigh muscles of seven subjects were imaged on an MRI scanner while performing isometric knee extensions at 40% maximal voluntary contraction. A gated velocity-encoded phase contrast MRI sequence in axial orientations yielded tissue velocity-encoded dynamic images of the four different compartments of the thigh muscles (vastus lateralis (VL), vastus medialis (VM), vastus intermedius (VI), and rectus femoris (RF)) at three longitudinal locations of the proximal–distal length: 17.5% (proximal), 50% (middle), and 77.5% (distal). The displacement, which is the time integration of the measured velocity, was calculated along the three orthogonal axes using a tracking algorithm. Results: The displacement of the muscle tissues was clearly nonuniform within each axial section as well as between the three axial locations. The ensemble average of the magnitude of the total displacement as a synthetic vector of the X, Y, and Z displacements was significantly larger in the VM at the middle location (p < 0.01), and in the VI at the distal location than in the other three muscles. The ensemble average of Z-axis displacement, which was almost aligned with the line of action, was significantly larger in VI than in the other three muscles in all three locations. Displacements of more than 20 mm were observed around the central aponeuroses, such as those between VI and the other surrounding muscles. Conclusions: These results imply that the quadriceps muscles act as one functional unit in normal force generation through the central aponeuroses despite complex behavior in each of the muscles, each of which possesses different physiological characteristics and architectures.

CFD validation using in-vitro MRI velocity data – Methods for data matching and CFD error quantification

Predicting blood flow velocities in patient-specific geometries with Computational Fluid Dynamics (CFD) can provide additional data for diagnosis and treatment planning but the solution can be inaccurate. Therefore, it is crucial to understand the simulation errors and calibrate the numerical model. In-vitro velocity-encoded MRI is a versatile tool to validate CFD. The comparison between CFD and in-vitro MRI velocity data, and the analysis of the simulation error are the objectives of this study. A three-step routine is presented to validate medical CFD data. First, a properly scaled model of the patient-specific geometry is fabricated to achieve high relative resolution in the MRI experiment. Second, the measured flow geometry is matched with the CFD data using one of two algorithms, Coherent Point Drift and Iterative Closest Point. The aligned data sets are then interpolated onto a common grid to enable a point-to-point comparison. Third, the global and local deviations between CFD and MRI velocity data are calculated using different algorithms to reliably estimate the simulation error. The routine is successfully tested with a patient-specific model of a cerebral aneurysm. In conclusion, the methods presented here provide a framework for CFD validation using in-vitro MRI velocity data.

From 2D to 4D Phase-Contrast MRI in the Neurovascular System: Will It Be a Quantum Jump or a Fancy Decoration?

Considering the crosstalk between the flow and vessel wall, hemodynamic assessment of the neurovascular system may offer a well-integrated solution for both diagnosis and management by adding prognostic significance to the standard CT/MR angiography. 4D flow MRI or time-resolved 3D velocity-encoded phase-contrast MRI has long been promising for the hemodynamic evaluation of the great vessels, but challenged in clinical studies for assessing intracranial vessels with small diameter due to long scan times and low spatiotemporal resolution. Current accelerated MRI techniques, including parallel imaging with compressed sensing and radial k-space undersampling acquisitions, have decreased scan times dramatically while preserving spatial resolution. 4D flow MRI visualized and measured 3D complex flow of neurovascular diseases such as aneurysm, arteriovenous shunts, and atherosclerotic stenosis using parameters including flow volume, velocity vector, pressure gradients, and wall shear stress. In addition to the noninvasiveness of the phase contrast technique and retrospective flow measurement through the wanted windows of the analysis plane, 4D flow MRI has shown several advantages over Doppler ultrasound or computational fluid dynamics. The evaluation of the flow status and vessel wall can be performed simultaneously in the same imaging modality. This article is an overview of the recent advances in neurovascular 4D flow MRI techniques and their potential clinical applications in neurovascular disease. LEVEL OF EVIDENCE: 5 TECHNICAL EFFICACY STAGE: 3.

Improved acceleration of phase-contrast flow imaging with magnitude difference regularization

PurposeTo develop a regularized image reconstruction algorithm for improved scan acceleration of phase-contrast (PC) flow MRI. MethodsBased on the magnitude similarity between bipolar-encoded k-space data, magnitude-difference regularization was incorporated into the conventional compressed sensing (CS) reconstruction. The gradient of the magnitude regularization was derived so the reconstruction problem can be solved using non-linear conjugate gradient with backtracking line search. Phase contrast flow data obtained in the peripheral arteries of healthy and patient subjects were retrospectively undersampled for testing the proposed reconstruction method. Three-dimensional velocity-encoded PC flow MRI was performed with prospective 4-fold undersampling for measuring arotic flow velocity in a healthy volunteer. ResultsIn the femoral arteries of healthy volunteers, the root-mean-square (RMS) errors of mean velocities were 0.56 ± 0.09 cm/s with CS-only reconstruction and 0.46 ± 0.08 cm/s with addition of magnitude regularization for three-fold acceleration; 1.34 ± 0.17 cm/s (CS only) and 1.08 ± 0.15 cm/s (magnitude regularized) for four-fold acceleration. In the iliac arteries of the patient, the RMS errors of mean velocities were 0.72 ± 0.12 cm/s and 0.56 ± 0.10 for three-fold acceleration, and 1.75 ± 0.21 and 1.24 ± 0.19 cm/s for four-fold acceleration (in the order of CS-only and magnitude regularized reconstructions). In the popliteal arteries, the RMS errors were 0.61 ± 0.10 cm/s and 0.42 ± 0.11 for three-fold acceleration, and 1.41 ± 0.19 and 1.12 ± 0.17 cm/s for four-fold acceleration. The maximum through-plane mean flow velocities were measured as 63.2 cm/s and 84.5 cm/s in ascending and descending aortas, respectively. ConclusionThe addition of magnitude-difference regularization into conventional CS reconstruction improves the accuracy of image reconstruction using highly undersampled phase-contrast flow MR data.

Efficient triple-VENC phase-contrast MRI for improved velocity dynamic range.

To evaluate the utility of an efficient triple velocity-encoding (VENC) 4D flow MRI implementation to improve velocity unwrapping of 4D flow MRI data with the same scan time as an interleaved dual-VENC acquisition. A balanced 7-point acquisition was used to derive 3 sets of 4D flow images corresponding to 3 different VENCs. These 3 datasets were then used to unwrap the aliased lowest VENC into a minimally aliased, triple-VENC dataset. Triple-VENC MRI was evaluated and compared with dual-VENC MRI over 3 different VENC ranges (50-150, 60-150, and 60-180 cm/s) in vitro in a steadily rotating phantom as well as in a pulsatile flow phantom. In vivo, triple-VENC data of the thoracic aorta were also evaluated in 3 healthy volunteers (2 males, 26-44 years old) with VENC = 50/75/150 cm/s. Two triple-VENC (triconditional and biconditional) and 1 dual-VENC unwrapping algorithms were quantitatively assessed through comparison to a reference, unaliased, single-VENC scan. Triple-VENC 4D flow constant rotation phantom results showed high correlation with the analytical solution (intraclass correlation coefficient = 0.984-0.995, P < .001) and up to a 61% reduction in velocity noise compared with the corresponding single-VENC scans (VENC = 150, 180 cm/s). Pulsatile flow phantom experiments demonstrated good agreement between triple-VENC and single-VENC acquisitions (peak flow < 0.8% difference; peak velocity < 11.7% difference). Triconditional triple-VENC unwrapping consistently outperformed dual-VENC unwrapping, correctly unwrapping more than 83% and 46%-66% more voxels in vitro and in vivo, respectively. Triple-VENC 4D flow MRI adds no additional scan time to dual-VENC MRI and has the potential for improved unwrapping to extend the velocity dynamic range beyond dual-VENC methods.

Patient-specific requirements and clinical validation of MRI-based pressure mapping: A two-center study in patients with aortic coarctation.

Invasive peak-to-peak pressure gradients are the current clinical reference standard for assessing aortic coarctation. To obtain them, patients need to undergo arterial heart catheterization. Unless an intervention is performed, the procedure remains purely diagnostic, while the concomitant risks remain. To validate MRI-based pressure mapping against pressure drop derived from heart catheterization and to define minimal clinical requirements. Prospective clinical validation study. Twenty-seven coarctation patients with an indicated heart catheterization were enrolled at two clinical centers. 1.5T including 4D velocity-encoded MRI and 3D anatomical imaging of the aorta. Pressure drop across the stenosis was calculated by pressure mapping based on the pressure Poisson equation. Calculated pressure drops were compared with catheter measured data. Spatial and temporal resolution were analyzed using in silico phantom-based data as well as in vivo measurements. Pressure drop was compared to peak-to-peak measurements. A two-sample paired mean equivalence test was used. In patients without imaging artifacts and a required spatial resolution ≥5 voxel/diameter, significant equivalence of pressure mapping compared to heart catheterization was found (17.5 ± 6.49 vs. 16.6 ± 6.53 mmHg, P < 0.001). Pressure mapping provides equivalent accuracy to pressure drop obtained from heart catheterization in patients 1) without previous stenting and 2) with sufficient spatial image resolution (at least 5 voxels/diameter). In these patients the method can reliably be performed prior to the actual procedure, and thus allows safe noninvasive treatment planning based on MRI. 2 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2019;49:81-89.

Novel 4D-Flow MRI to Assess Quantitative Arterial Hemodynamic Response after Brain Stereotactic Radiosurgery (SRS) for Cerebral Arteriovenous Malformations (AVMs)

For unresectable cerebral AVMs, ablative SRS is standard of care. However, obliteration may take years, during which period risk of hemorrhage is uncertain. 4D-Flow MRI, a velocity-encoded phase-contrast MRI technique used to assess cardiac hemodynamics, has potential as an early marker of treatment response to SRS. Here, we assess changes in blood flow in AVM feeding arteries after brain SRS using 4D-Flow. Patients: Retrospective review of AVM patients treated with SRS at a single institution. Four patients were identified who underwent 4D-Flow MRI prior to or within 1 month of treatment (baseline) and at least one subsequent time point (first-follow up). Imaging: Imaging was performed on a 3T scanner with dedicated head coil. 4D-Flow sequences were based on a 3D spoiled gradient echo sequence with resolution 1.12 x 0.98 x 1.6-1.8 mm. Three directional velocity encoding gradients were used with Venc 100-200 cm/s. In addition, T1 post-contrast, T2, and 3D-Time of flight (TOF) angiography images were obtained to identify the AVM nidus and feeding arteries. Analysis: In each case a feeding artery was selected that could be traced distally to the AVM on both baseline and follow up images. Measurements were made in two locations within each feeding artery. A distal measurement was made as close to the AVM nidus as possible. A proximal measurement was made in the most proximal segment of the feeding artery (e.g. M1 segment of MCA). A control measurement was made in the corresponding contralateral proximal artery. Blood flow was measured using imaging software with FDA clearance for clinical 4D flow post-processing for cardiac MRI. Changes in blood flow were assessed for significance using two-tailed paired t-tests. Baseline AVM nidus volume ranged from 4.6-10.2mL. All AVMs were treated with single fraction SRS, prescription dose 16-20 Gy. Follow up time ranged from 3-17 months. Baseline and follow up blood flow measurements in L/min are displayed in table 1. In feeding arteries, blood flow decreased by a mean of 49% proximally and by 54% distally (both p<0.05). There was no detectable change in blood flow in control arteries (mean change 12%, p = 0.28). Blood flow through cerebral AVM feeding arteries decreases significantly after SRS by time of first follow up as assessed by 4D-Flow MRI. 4D-Flow is a promising early marker of AVM response to SRS. Future studies are needed to determine if this hemodynamic response correlates to decreased risk of hemorrhage prior to radiographic AVM obliteration.Abstract 232; Table 1PatientSpetzler-Martin GradeDistal BaselineDistal Follow UpProximal BaselineProximal Follow UpControl BaselineControl Follow Up130.120.040.500.210.230.24240.290.130.560.280.030.05340.160.070.410.180.080.07420.420.240.510.350.250.26meann/a0.250.120.490.250.150.16SDn/a0.130.080.070.070.100.10 Open table in a new tab

4D-Flow MRI: Technique and Applications.

Blood flow through the cavities of the heart and great vessels is pulsatile and is subject to time and multidirectional variations. To date, the recording of blood flow in multiple directions and phases has been limited. 4D-flow MRI offers advantages for the recording, visualization and analysis of blood flow. The status quo of the method was summarized through analysis with the PubMed database using the keywords "4D-flow MRI, phase-contrast magnetic resonance imaging, MR flow imaging/visualization, MR flow quantification, 3 D cine (time-resolved) phase-contrast CMR, three-directional velocity-encoding MRI". This review summarizes the current status of the technical development of 4D-flow MRI, discusses its advantages and disadvantages and describes clinical applications. Finally, the most important principles and parameters are explained to give the reader relevant information about clinical indications, postprocessing methods and limitations of the method. · 4D-Fluss-MRT. · 3-dimensionale zeitaufgelöste Phasenkontrast-MRT. · Flussanalyse-MRT (Wall-Shear-Stress/Druckgradienten-Messung/Vortex-Fluss/turbulente kinetische Energie/Flussgeschwindigkeit/Flussrate). · Sträter A, Huber A, Rudolph J et al. 4D-Flow MRI: Technique and Applications. Fortschr Röntgenstr 2018; 190: 1025 - 1035.

Shear strain rate from phase contrast velocity encoded MRI: Application to study effects of aging in the medial gastrocnemius muscle.

Strain rate (SR) is a measure of the rate of regional deformation that can be computed by analyzing velocity-encoded phase-contrast 2D images. Recent studies have explored the changes in normal components of the strain tensor in aging muscle, while shear strain may also provide valuable information. To compute the shear SR from velocity-encoded MRI of the lower leg and to study the correlation of SR parameters measured in the medial gastrocnemius (MG) to muscle force in a cohort of young and senior subjects. Prospective cohort study. Six young (26.1 ± 2.3 years) and six senior (76.7 ± 8.3 years) healthy females; two other subjects were scanned on three separate occasions for repeatability studies. 1.5T using a single oblique sagittal slice with velocity-encoding in three directions (velocity-encoded phase contrast gradient echo sequence). Age-related and regional differences in the SR eigenvalues (SRfiber , SRin-plane ), normal SRs (SRff , SRcc ), and shear SRs (SRfc , SRfc_max ) were statistically analyzed. Difference between young and senior cohorts were assessed using two-way analysis of variance (ANOVAs). The coefficient of variation and repeatability coefficient were calculated from repeat studies. Univariate and stepwise multivariable linear regression was performed to identify predictors of force. During isometric plantarflexion contraction, SRs in the principal basis (SRfiber , SRin-plane ) and maximum shear SR (SRfc_max ) was significantly lower in the senior cohort (P < 0.05). On multiple variable regression, maximum shear SR (SRfc_max ) and normal SR in the fiber cross-section (SRcc ) were significantly associated with force (R = 0.681, F = 14.034, P < 0.001). This study establishes that computation of shear strain is feasible and is a significant predictor of force variability with age. 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:1351-1357.

Relationship of changes in strain rate indices estimated from velocity-encoded MR imaging to loss of muscle force following disuse atrophy.

This study explores changes in strain rate (SR) (rate of regional deformation) parameters extracted from velocity-encoded MRI and their relationship to muscle force loss following 4-week unilateral lower limb suspension in healthy humans. Two-dimensional SR maps were derived from three directional velocity-encoded MR phase-contrast images of the medial gastrocnemius in seven subjects. Atrophy-related and regional differences in the SR eigenvalues, angle between the SR and muscle fiber (SR-fiber angle), and strain rates in the fiber basis were statistically analyzed using analysis of variance and linear regression. During isometric contraction, SR in the fiber cross section (SRin-plane ) was significantly lower, and the SR-fiber angle was significantly higher postsuspension (P < 0.05). On multiple variable regression analysis, the volume of medial gastrocnemius, SRin-plane , and SR-fiber angle were significantly associated with force and changes in the, and the SR eigenvalues and shear SR were significantly associated with change in force with disuse. Changes in SR-fiber angle, SRin-plane , and shear SR as well as their ability to predict force and force changes may reflect the role of remodeling of the extracellular matrix in disuse atrophy and its functional consequence in reducing lateral transmission of force. Magn Reson Med 79:912-922, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

DNA methylation at birth within the promoter of ANRIL predicts markers of cardiovascular risk at 9years.

AimsAntisense non-coding RNA in the INK4 locus (ANRIL) fixed genetic variants have consistently been linked with coronary heart disease (CHD) risk. We investigated relationships between perinatal ANRIL promoter DNA methylation and CHD risk markers in children aged 9 years. Genetic variants in the non-coding RNA ANRIL identify it as an important CHD risk locus. Increasing evidence suggests that the early life environment may act through epigenetic processes to influence later CHD risk markers such as increased arterial pulse wave velocity (PWV, a measure of arterial stiffness) blood pressure or heart rate.Methods and resultsUsing pyrosequencing, ANRIL DNA methylation at nine CpG sites was measured in the umbilical cord from 144 children in a UK mother-offspring cohort and related to the descending aorta PWV measured by velocity-encoded phase contrast MRI at age 9 years. Perinatal methylation was not associated with child’s later blood pressure, but higher methylation at CpG5 was associated with increased childhood PWV (β = 0.066 m/s/10 % methylation increase [95 % CI, 0.004 to 0.128], p = 0.037); 10 % decreases in methylation at CpG1 and CpG2 were associated with increased heart rate (CpG1 β = 1.93 [0.07 to 3.8] beats/min, p = 0.041; CpG2 β = 2.30 [0.18 to 4.41] beats/min, p = 0.033, accounting for potential confounding variables). The associations with perinatal ANRIL promoter methylation were independent of neighbouring fixed genetic variants.ConclusionsOur findings suggest developmental epigenetic regulation of ANRIL promoter methylation as a factor in later CHD risk in children.Electronic supplementary materialThe online version of this article (doi:10.1186/s13148-016-0259-5) contains supplementary material, which is available to authorized users.

Dilatation of the ascending aorta is associated with presence of aortic regurgitation in patients after repair of tetralogy of Fallot

To evaluate the association between aortic morphology and elasticity with aortic regurgitation in surgically corrected of tetralogy of Fallot (TOF) patients. We retrospectively identified 72 consecutive patients with surgically corrected TOF and 27 healthy controls who underwent cardiac MRI evaluation. Velocity-encoded cine MRI was used to quantify degree of aortic regurgitation (AR) in TOF patients. Ascending aorta diameters were measured at standard levels on MRA images. Aortic pulse-wave velocity (PWV) was quantified with MRI. Morphological and functional MRI variables were compared between groups of TOF patients with and without clinically relevant AR and controls. The association between aortic morphology and elasticity with the presence of AR was evaluated using univariate and multivariate logistic regression. The majority of TOF patients had only trace AR. Nine TOF patients (12 %) had an AR fraction higher than 15 %. Indexed aorta diameter at the sinotubular junction (p = 0.007), at the RPA level (p = 0.006), and low left ventricular ejection fraction (LVEF) (p = 0.015) showed the strongest associations with the presence of at least mild AR, which persisted after controlling for age and gender. Increased ascending aorta dimension is associated with AR in patients after repair of TOF. LVEF was also low in the group of patients with relevant AR compared to those without, suggesting even mild to moderate AR may contribute to LV dysfunction in these patients. Enlarged ascending aorta may be an indication for precise quantification of regurgitant fraction with MRI, since symptomatic patients may need aortic valve repair when moderate regurgitation is present.

Aortic valve planimetry by high-resolution 3-dimensional MR image acquisition with a breath-hold: comparison with conventional cine MR imaging and echocardiography to assess the severity of aortic valve stenosis

Methods In 88 consecutive patients (66.9 ± 9.59 years, 63% men) with varying degrees of aortic valve stenosis, high-resolution 3D SSFP images (3D planimetry; 2.0 mm slice thickness, 20 contiguous slices; image matrix, 256 ‘ 209) were acquired with single breath-hold during mid systole and mid diastole. SSFP cine MR imaging (2D planimetry) and velocity-encoded cine MRI (slice thickness, 4.5 mm) in three levels of aortic valve were also performed. AVA area was measured by two experienced observers using commercial software (iNtuition, TeraRecon). MR imaging measurements and image quality were compared with transthoracic echocardiographic measurements of effective aortic orifices (EAO) using the continuity equation (1 = severe blurring of images, 2 = moderate blurring of valve contours; 3 = mild blurring of valve contours, 4 = excellent and no artifact). Sensitivity for accurate measurement and receiver operating characteristic (ROC) curve were calculated. Intraand interobserver agreements were determined by using intraclass correlation coefficient (ICC). Results Mean AVA derived by 3D planimetry, 2D planimetry, and echocardiography were 0.77 ± 1.04 cm, 0.72 ± 1.16 cm, and 0.75 ± 0.32 cm, respectively. The ICC value of 3D planimetry was higher than 2D planimetry [0.799 (CI, 0.691-0.869) vs. 0.743 (CI, 0.605-0.832)] with echocardiographic EAO as the standard of reference. The grade of image quality of 3D planimetry was superior to 2D planimetry (3.65 ± 0.65 vs. 3.17 ± 0.65). The correlation coefficients of maximum peak velocity on velocity-encoded cine MR imaging with 3D planimetry and that with 2D planimetry were 0.42 (p < 0.05) and 0.35 (p < 0.05). Intraand interobserver agreements for 3D planimetry were excellent [ICC = 0.949 (CI, 881-979) and 0.846 (CI, 0.636-0.935), respectively; both, p = 0.000).