4D Flow Sequence Research Articles

3D Vortex-Energetics in the Left Pulmonary Artery for Differentiating Pulmonary Arterial Hypertension and Pulmonary Venous Hypertension Groups Using 4D Flow MRI.

Pulmonary hypertension (PH) is a life-threatening. Differentiation pulmonary arterial hypertension (PAH) from pulmonary venous hypertension (PVH) is important due to distinct treatment protocols. Invasive right heart catheterization (RHC) remains the reference standard but noninvasive alternatives are needed. To evaluate 4D Flow MRI-derived 3D vortex energetics in the left pulmonary artery (LPA) for distinguishing PAH from PVH. Prospective case-control. Fourteen PAH patients (11 female) and 18 PVH patients (9 female) diagnosed from RHC, 23 healthy controls (9 female). 1.5 T; gradient recalled echo 4D flow and balanced steady-state free precession (bSSFP) cardiac cine sequences. LPA 3D vortex cores were identified using the lambda2 method. Peak vortex-contained kinetic energy (vortex-KE) and viscous energy loss (vortex-EL) were computed from 4D flow MRI. Left and right ventricular (LV, RV) stroke volume (LVSV, RVSV) and ejection fraction (LVEF, RVEF) were computed from bSSFP. In PH patients, mean pulmonary artery pressure (mPAP), pulmonary capillary wedge pressure (PCWR) and pulmonary vascular resistance (PVR) were determined from RHC. Mann-Whitney U test for group comparisons, Spearman's rho for correlations, logistic regression for identifying predictors of PAH vs. PVH and develop models, area under the receiver operating characteristic curve (AUC) for model performance. Significance was set at P < 0.05. PAH patients showed significantly lower vortex-KE (37.14 [14.68-78.52] vs. 76.48 [51.07-120.51]) and vortex-EL (9.93 [5.69-25.70] vs. 24.22 [12.20-32.01]) than PVH patients. The combined vortex-KE and LVEF model achieved an AUC of 0.89 for differentiating PAH from PVH. Vortex-EL showed significant negative correlations with mPAP (rho = -0.43), PCWP (rho = 0.37), PVR (rho = -0.64). In the PAH group, PVR was significantly negatively correlated with LPA vortex-KE (rho = -0.73) and vortex-EL (rho = -0.71), and vortex-KE significantly correlated with RVEF (rho = 0.69), RVSV, (rho = 0.70). In the PVH group, vortex-KE (rho = 0.52), vortex-EL significantly correlated with RVSV (rho = 0.58). These preliminary findings suggest that 4D flow MRI-derived LPA vortex energetics have potential to noninvasively differentiate PAH from PVH and correlate with invasive hemodynamic parameters. 1 TECHNICAL EFFICACY: Stage 3.

Direct comparison of whole heart quantifications between different retrospective and prospective gated 4D flow CMR acquisitions.

4D flow cardiovascular magnetic resonance (CMR) is a versatile technique to non-invasively assess cardiovascular hemodynamics. With developing technology, choice in sequences and acquisition parameters is expanding and it is important to assess if data acquired with these different variants can be directly compared, especially when combining datasets within research studies. For example, sequences may allow a choice in gating techniques or be limited to one method, yet there is not a direct comparison investigating how gating selection impacts quantifications of the great vessels, semilunar and atrioventricular valves and ventricles. Thus, this study investigated if quantifications across the heart from contemporary 4D flow sequences are comparable between two commonly used 4D flow sequences reliant on different ECG gating techniques. Forty participants (33 healthy controls, seven patients with coronary artery disease and abnormal diastolic function) were prospectively recruited into a single-centre observational study to undergo a 3T-CMR exam. Two acquisitions, a k-t GRAPPA 4D flow with prospective gating (4Dprosp) and a modern compressed sensing 4D flow with retrospective gating (4Dretro), were acquired in each participant. Images were analyzed for volumes, flow rates and velocities in the vessels and four valves, and for biventricular kinetic energy and flow components. Data was compared for group differences with paired t-tests and for agreement with Bland-Altman and intraclass correlation (ICC). Measurements primarily occurring during systole of the great vessels, semilunar valves and both left and right ventricles did not differ between acquisition types (p > 0.05 from t-test) and yielded good to excellent agreement (ICC: 0.75-0.99). Similar findings were observed for the majority of parameters dependent on early diastole. However, measurements occurring in late diastole or those reliant on the entire-cardiac cycle such as flow component volumes along with diastolic kinetic energy values were not similar between 4Dprosp and 4Dretro acquisitions resulting in poor agreement (ICC < 0.50). Direct comparison of measurements between two different 4D flow acquisitions reliant on different gating methods demonstrated systolic and early diastolic markers across the heart should be compatible when comparing these two 4D flow sequences. On the other hand, late diastolic and intraventricular parameters should be compared with caution.

Association of Impaired Left Ventricular Mitral Filling from 4D Flow Cardiac MRI and Prognosis of Hypertrophic Cardiomyopathy.

Purpose To investigate whether the peak early filling rate normalized to the filling volume (PEFR/FV) estimated from four-dimensional (4D) flow cardiac MRI may be used to assess impaired left ventricular (LV) filling and predict clinical outcomes in individuals with hypertrophic cardiomyopathy (HCM). Materials and Methods Cardiac MRI with a 4D flow sequence and late gadolinium enhancement (LGE), as well as echocardiography, was performed in 88 individuals: 44 participants with HCM from a French prospective registry (ClinicalTrials.gov; NCT01091480) and 44 healthy volunteers matched for age and sex. In participants with HCM, a composite primary end point was assessed at follow-up, including unexplained syncope, new-onset atrial fibrillation, hospitalization for congestive heart failure, ischemic stroke, sustained ventricular arrhythmia, septal reduction therapy, and cardiac death. A Cox proportional hazard model was used to analyze associations with the primary end point. Results PEFR/FV was significantly lower in the HCM group (mean age, 51.8 years ± 18.5 [SD]; 29 male participants) compared with healthy volunteers (mean, 3.35 sec-1 ± 0.99 [0.90-5.20] vs 4.42 sec-1 ± 1.68 [2.74-11.86]; P < .001) and correlated with both B-type natriuretic peptide (BNP) level (r = -0.31; P < .001) and the ratio of pulsed Doppler early transmitral inflow to Doppler tissue imaging annulus velocities (E/E'; r = -0.54; P < .001). At a median follow-up of 2.3 years (IQR, 1.7-3.3 years), the primary end point occurred in 14 (32%) participants. A PEFR/FV of 2.61 sec-1 or less was significantly associated with occurrence of the primary end point (hazard ratio, 9.46 [95% CI: 2.61, 45.17; P < .001] to 15.21 [95% CI: 3.51, 80.22; P < .001]), independently of age, BNP level, E/E', LGE extent, and LV and left atrial strain according to successive bivariate models. Conclusion In HCM, LV filling evaluated with 4D flow cardiac MRI correlated with Doppler and biologic indexes of diastolic dysfunction and predicted clinical outcomes. Keywords: Diastolic Function, Left Ventricular Filling, Hypertrophic Cardiomyopathy, Cardiac MRI, 4D Flow Sequence Clinical trial registration no. NCT01091480 Supplemental material is available for this article. © RSNA, 2024.

MRI Investigation of the Association of Left Atrial and Left Atrial Appendage Hemodynamics with Silent Brain Infarction.

Left atrial (LA) myopathy is thought to be associated with silent brain infarctions (SBI) through changes in blood flow hemodynamics leading to thrombogenesis. 4D-flow MRI enables in-vivo hemodynamic quantification in the left atrium (LA) and LA appendage (LAA). To determine whether LA and LAA hemodynamic and volumetric parameters are associated with SBI. Prospective observational study. A single-site cohort of 125 Participants of the multiethnic study of atherosclerosis (MESA), mean age: 72.3 ± 7.2 years, 56 men. 1.5T. Cardiac MRI: Cine balanced steady state free precession (bSSFP) and 4D-flow sequences. Brain MRI: T1- and T2-weighted SE and FLAIR. Presence of SBI was determined from brain MRI by neuroradiologists according to routine diagnostic criteria in all participants without a history of stroke based on the MESA database. Minimum and maximum LA volumes and ejection fraction were calculated from bSSFP data. Blood stasis (% of voxels <10 cm/sec) and peak velocity (cm/sec) in the LA and LAA were assessed by a radiologist using an established 4D-flow workflow. Student's t test, Mann-Whitney U test, one-way ANOVA, chi-square test. Multivariable stepwise logistic regression with automatic forward and backward selection. Significance level P < 0.05. 26 (20.8%) had at least one SBI. After Bonferroni correction, participants with SBI were significantly older and had significantly lower peak velocities in the LAA. In multivariable analyses, age (per 10-years) (odds ratio (OR) = 1.99 (95% confidence interval (CI): 1.30-3.04)) and LAA peak velocity (per cm/sec) (OR = 0.87 (95% CI: 0.81-0.93)) were significantly associated with SBI. Older age and lower LAA peak velocity were associated with SBI in multivariable analyses whereas volumetric-based measures from cardiac MRI or cardiovascular risk factors were not. Cardiac 4D-flow MRI showed potential to serve as a novel imaging marker for SBI. 3 TECHNICAL EFFICACY: Stage 2.

Assessment of paravalvular regurgitation after transcatheter aortic valve replacement using 2D multi-venc and 4D flow CMR.

To compare the novel 2D multi-venc and 4D flow acquisitions with the standard 2D flow acquisition for the assessment of paravalvular regurgitation (PVR) after TAVR using cardiac magnetic resonance (CMR)-derived regurgitant fraction (RF). In this prospective study, patients underwent CMR one month after TAVR to assess PVR using 2D multi-venc and 4D flow, in addition to standard 2D flow. Scatterplots and Bland-Altman plots were used to assess correlation and visualize agreement between techniques. Reproducibility of measurements was assessed with intraclass correlation coefficients. The study included 21 patients (mean age, 80 years ± 5 [SD], 9 men). Mean RF was 11.7 ± 10.0% using standard 2D flow, 10.6 ± 7.0% using 2D multi-venc flow, and 9.6 ± 7.3% using 4D flow. There was a very strong correlation between the RFs assessed with 2D multi-venc and standard 2D flow (r = 0.88, p < 0.001), and a strong correlation between the RFs assessed with 4D flow and standard 2D flow (r = 0.74, p < 0.001). Bland-Altman plots revealed no significant bias between the RFs (2D multi-venc: 1.3%; 4D flow: 0.3%). Intra- and interobserver reproducibility for 2D multi-venc flow were 0.98 and 0.97, respectively; and 0.92 and 0.90 for 4D flow, respectively. 2D multi-venc and 4D flow produce accurate quantification of PVR after TAVR. The fast acquisition of the 2D multi-venc sequence, and the free-breathing acquisition with retrospective plane selection of the 4D flow sequence provide useful advantages in clinical practice, especially in the frail TAVR population.

Quantitative Flow Measurements of Pelvic Venous Vasculature Using 4D Flow MRI

To evaluate 4D Flow magnetic resonance imaging (MRI) sequences for quantitative flow measurements of the pelvic venous vasculature. A prospective study of healthy volunteers was performed. After informed consent all subjects underwent 4D flow sequences at a 3 T MRI scanner with different isotropic resolution and different velocity encoding (Venc) settings: (sequence #1) voxel size (VS) 1.63 mm3, Venc 50cm/s; (sequence #2) VS 1.63 mm3, Venc 100cm/s and (sequence #3) VS 2.03 mm3, Venc 50cm/s. Perfusion parameters were calculated for all venous vessel segments starting at the level of the inferior vena cava and extending caudally to the level of the common femoral vein. For reference, arterial flow was calculated using 1.63 mm3 isotropic resolution with a Venc of 100cm/s. Ten healthy subjects (median age 28 years, interquartile range [IQR]: 26.25-28 years) were enrolled in this study. Median scanning time was 12:12 minutes (IQR 10:22-13:32 minutes) for sequence #1, 11:02 minutes (IQR 9:57-11:19 minutes) for sequence #2 and 6:10 minutes (IQR 5:44-6:47 minutes) for sequence #3. Flow measurements were derived from all sequences. The venous pelvic vasculature showed similar perfusion parameters compared to its arterial counterpart, for example the right common iliac arterial segment showed a perfusion of 8.32ml/s (IQR: 6.94-10.68ml/s) versus 7.29ml/s (IQR: 4.70-8.90ml/s) in the corresponding venous segment (P=0.218). The venous flow measurements obtained from the three investigated sequences did not reveal significant differences. 4D Flow MRI is suitable for quantitative flow measurement of the venous pelvic vasculature. To reduce the scanning time without compromising quantitative results, the resolution can be decreased while increasing the Venc. This technique may be utilized in the future for the diagnosis and treatment response assessment of iliac vein compression syndromes.

Differentiation Between the Low and High Trans-Stenotic Pressure Gradient in Patients With Idiopathic Intracranial Hypertension Using 4D Flow MRI-Derived Hemodynamic Parameters.

Trans-stenotic pressure gradient (TPG) measurement is essential for idiopathic intracranial hypertension (IIH) patients with transverse sinus (TS) stenosis. Four-D flow MRI may provide a noninvasive imaging method for differentiation of IIH patients with different TPG. To investigate the associations between 4D flow parameters and TPG, and to evaluate the diagnostic performance of 4D flow parameters in differentiating patients with high TPG (GroupHP) from low TPG (GroupLP). Prospective. 31 IIH patients with TS stenosis (age, 38 ± 12 years; 23 females) and 5 healthy volunteers (age, 25 ± 1 years; 2 females). 3T, 3D phase contrast MR venography, and gradient recalled echo 4D flow sequences. Scan-rescan reproducibility of 4D flow parameters were performed. The correlation between TPG and flow parameters was analyzed. The netflow and velocity difference between inflow plane, outflow plane, and the stenosis plane were calculated and compared between GroupHP and GroupLP. Pearson's correlation or Spearman's rank correlation coefficient, Independent samples t-test or Wilcoxon rank-sum test, Intra-class correlation coefficient (ICC), Bland-Altman analyses, Receiver operating characteristic curves. A P value <0.05 was considered significant. Significant correlations were found between TPG and netflow parameters including Favg,out-s, Favg,in-s, Fmax,out-s, and Fmax,in-s (r = 0.525-0.565). Significant differences were found in Favg,out-s, Fmax,out-s, Favg,in-s, and Fmax,in-s between GroupHP and GroupLP. Using the cut-off value of 2.19 mL/sec, the Favg,out-s showed good estimate performance in distinguishing GroupHP from GroupLP (AUC = 0.856). The ICC (ranged 0.905-0.948) and Bland-Altman plots indicated good scan-rescan reproducibility. 4D flow MRI derived flow parameters showed good correlations with TPG in IIH patients with TS stenosis. Netflow difference between outflow and stenosis location at TS shows the good performance in differentiating GroupHP and GroupLP cases. 2 TECHNICAL EFFICACY: Stage 2.

Comparison of free-running whole-heart 5D and 4D flow imaging to standard 2D phase contrast in patients with right-sided congenital heart disease

Abstract Funding Acknowledgements Type of funding sources: None. Background Flow measurements by cardiac magnetic resonance (CMR) are part of a routine assessment in patients with congenital heart disease (CHD). Standard 2D phase contrast (2DPC) sequences, however, require precise prescription of image planes leading to long scan times which could be overcome by 3D-acquisitons covering the entire cardiac anatomy in a single acquisition. Thus, recently introduced accelerated free-breathing 3D whole heart flow sequences promise to simplify CMR exams allowing an easier acquisition and retrospective flow measurements in virtually all vessels. Purpose Comparison of standard 2DPC to an accelerated 4D flow sequence with prospective respiratory navigation (1), and a free-running radial fully self-gated respiratory and cardiac motion-resolved 5D flow sequence (5D flow) (2,3). Methods Patients with right-sided CHD and no intra- or extracardiac shunt underwent a CMR on a 1.5T scanner. 2DPC flow sequences and a 4D flow data set were obtained (1). In addition, a whole-heart free-running 3D radial PC CMR sequence was acquired (2). Using a compressed-sensing-based image reconstruction framework (2,3), 5D flow images were obtained, and the end-expiratory phase was used for analysis. 3D vessel segmentation was based on retrospectively computed phase-contrast angiography images for each 4D and 5D flow datasets. Flow measured in the ascending, descending aorta (AA, DA), main, right and left pulmonary artery (MPA, RPA, LPA) and superior vena cava (SVC) as well as the internal consistency for determination of systemic and pulmonary output were compared between all three sequences by Bland-Altman analyses. Results Twenty CHD patients (age 31±11y, 7 women, tetralogy of Fallot N=7, Ross operation N=10; pulmonary regurgitation, atrial switch and Ebstein’s disease each N=1) were included. Mean peak velocity of MPA/ right ventricle to pulmonary artery conduit was 1.9 (range 0.9; 3.5) m/s. Compared to 2DPC, both 4D and 5D flow moderately underestimated absolute flow with significant lower values for the RPA for 4D flow (Table 1). The bias (i.e. the mean absolute difference) of MPA flow between 2DPC and 4D flow was related to the MPA peak velocity (r2=0.3, p = 0.03) with a similar trend for the comparison of 2DPC vs. 5D flow (r2=0.142, p = 0.141). The comparison of the internal consistency for determination of systemic and pulmonary output showed similar results for 2DPC and 5D flow and a slightly lower agreement for the 4D flow sequence (Table 2). Conclusions In this preliminary study, 4D and 5D flow provide results comparable to 2DPC, however, both sequences showed a trend towards lower absolute flow values. Complex flow patterns due to the right-sided pathologies appear to have an impact on the difference observed between sequences as shown for the MPA. The internal consistency of flow quantification was similar for the 2DPC and 5D flow sequences. The presented observations are currently being evaluated in a larger study.

Four-Dimensional Flow MRI for the Evaluation of Aortic Endovascular Graft: A Pilot Study.

We aimed to explore the feasibility of 4D flow magnetic resonance imaging (MRI) for patients undergoing thoracic aorta endovascular repair (TEVAR). We retrospectively evaluated ten patients (two female), with a mean (±standard deviation) age of 61 ± 20 years, undergoing MRI for a follow-up after TEVAR. All 4D flow examinations were performed using a 1.5-T system (MAGNETOM Aera, Siemens Healthcare, Erlangen, Germany). In addition to the standard examination protocol, a 4D flow-sensitive 3D spatial-encoding, time-resolved, phase-contrast prototype sequence was acquired. Among our cases, flow evaluation was feasible in all patients, although we observed some artifacts in 3 out of 10 patients. Three individuals displayed a reduced signal within the vessel lumen where the endograft was placed, while others presented with turbulent or increased flow. An aortic endograft did not necessarily hinder the visualization of blood flow through 4D flow sequences, although the graft could generate flow artifacts in some cases. A 4D Flow MRI may represent the ideal tool to follow up on both healthy subjects deemed to be at an increased risk based on their anatomical characteristics or patients submitted to TEVAR for whom a surveillance protocol with computed tomography angiography would be cumbersome and unjustified.

A novel approach in the assessment of paravalvular regurgitation after transcatheter aortic valve replacement using cardiac magnetic resonance imaging

Abstract Funding Acknowledgements Type of funding sources: None. Background Paravalvular regurgitation (PVR) is a common complication after transcatheter aortic valve replacement (TAVR) that poses an increased risk of rehospitalization for heart failure and mortality. Two-dimensional (2D) cardiac magnetic resonance (CMR) quantitative flow assessment is the gold standard for evaluation of PVR after TAVR. Two novel techniques in flow assessment are 2D multi-velocity encoding (Venc) and four-dimensional (4D) flow. The 2D multi-venc sequence provides the advantage of integrating three different Venc values in a rapid, single breath-hold acquisition, specifically providing accurate measurements for both high and low velocities. 4D-flow allows a free-breathing acquisition with unlimited plane selection, and provides a comprehensive visualization of the blood flow. Although the use of these novel techniques is expanding, these have not yet been assessed for their correlation with standard 2D-flow. Purpose To compare the standard 2D-flow acquisition with both 2D multi-venc and 4D-flow acquisitions for the assessment of PVR using CMR-derived regurgitant fraction (CMR-RF). Methods In this substudy of the APPOSE trial (NCT04281771), 19 patients underwent CMR one month after TAVR using 2D multi-venc and 4D-flow, in addition to the standard 2D-flow acquisition. Medis Suite MR (Medis Medical Imaging, Leiden, the Netherlands) was used for analysis of the flow data. Scatterplots and Bland-Altman plots were used to assess correlation and visualize agreement between the techniques. Results Mean age was 79.8 ± 4.9 years, and 42.9% of the patients were men. Mean CMR-RF was 11.7 ± 10.0% using the standard 2D-flow sequence, 10.6 ± 7.0% using the 2D multi-venc sequence, and 9.6 ± 7.3% using the 4D-flow acquisition. Both the CMR-RF assessed with 2D multi-venc and 4D-flow showed a high correlation with the CMR-RF assessed with standard 2D-flow (r = 0.88, p &amp;lt; 0.001 and r = 0.74, p &amp;lt; 0.001, respectively). Bland-Altman plots revealed no significant bias between the mean values of CMR-RF (2D multi-venc: 1.31%; 4D-flow: 0.27%). Conclusion Both the 2D multi-venc and 4D-flow sequence produce accurate quantification of PVR after TAVR. Given the advantages of these approaches in terms of acquisition speed and plane selection, use of these techniques should be encouraged.

Characterization of impaired left ventricular mitral filling in HCM: A 4D-flow CMR study

Diastolic dysfunction is common and contributes to many clinical manifestations in hypertrophic cardiomyopathy (HCM). 4-dimensionnal (4D) flow cardiac magnetic resonance (CMR) sequence can assess left ventricular mitral filling. The purpose of this study was to determine if the peak early filling rate normalized to the filling volume (PEFR/FV), estimated from 4D-flow sequence can accurately assess impaired left ventricular mitral filling and predict clinical outcomes. This monocentric study included 44 HCM patients from a prospective HCM register and 44 healthy volunteers, who all underwent CMR with 4D-Flow sequence. Median follow-up time of HCM cohort patients was 2.3 years (interquartile range: 1.7 to 3.3 years). The predefined primary endpoint was a composite criteria that included syncope, onset of atrial fibrillation, admission for congestive heart failure with administration of diuretics, decision to perform septal reduction therapy due to persistent symptomatic obstruction, stroke, ventricular tachycardia or fibrillation and cardiac death. PEFR/FV was significantly lower in HCM cohort compared to healthy volunteers (P < 0.001). PFR/FV significantly correlated with BNP (r = −0.31, P < 0.001) and with E/E’ ratio (r = −0.56, p < 0.001). PEFR/FV according to NYHA status in HCM cohort was statistically different (P = 0.001). Primary endpoint occurred in 14 patients (32%). In univariate and bivariate adjusted cox-model analysis PEFR/FV < 2.61 s -1 was significantly associated with primary endpoint with Hazard Ratio ranging from [HR = 9.46 (95% CI 2.61–45.17, P < 0.001) to 15.21 (95%CI 3.51–80.22, P < 0.001)] according to succesive bivariate models. 4D-Flow can accurately assess left ventricular mitral filling with a good predictive value of clinical outcomes in HCM patients. Relation of PEFR/FV calculated with 4D flow in HCM.

4D-Flow Cardiovascular Magnetic Resonance Sequence for Aortic Assessment: Multi-Vendor and Multi-Magnetic Field Reproducibility in Healthy Volunteers.

Four-dimensional (4D) flow cardiac magnetic resonance (CMR) represents an emerging technique for non-invasive evaluation of the aortic flow. The aim of this study was to investigate a 4D-flow CMR sequence for the assessment of thoracic aorta comparing different vendors and different magnetic fields of MR scanner in fifteen healthy volunteers. CMR was performed on three different MRI scanners: one at 1.5 T and two at 3 T. Flow parameters and planar wall shear stress (WSS) were extracted from six transversal planes along the full thoracic aorta by three operators. Inter-vendor comparability as well as scan-rescan, intra- and interobserver reproducibility were examined. A high heterogeneity was found in the comparisons for each operator and for each scanner in the six transversal planes analysis (Friedman rank-sum test; p-value ≤ 0.05). Among all, the most reproducible measures were extracted for the sinotubular junction plane and for the flow parameters. Our results suggest that standardized procedures have to be defined to make more comparable and reproducible 4D-flow parameters and mainly, clinical impactfulness. Further studies on sequences development are needed to validate 4D-flow MRI assessment across vendors and magnetic fields also compared to a missing gold standard.

Application of 4D Flow MRI to Predict Clinical Outcomes after Stereotactic Radiosurgery (SRS) for Cerebral Arteriovenous Malformations (AVMs)

<h3>Purpose/Objective(s)</h3> SRS is standard of care for unresectable cerebral AVMs. Nidus obliteration is the standard clinical metric of treatment success but can take years to occur. Hemorrhage risk is uncertain during this latency period. We hypothesized that early changes in blood flow through feeding arteries after SRS would predict future nidus obliteration and hemorrhage risk. We used 4D flow MRI to prospectively measure blood flow in feeding arteries prior to and 6 months after AVM SRS and correlated the early blood flow response to SRS to later clinical outcomes. <h3>Materials/Methods</h3> <i>Patients:</i> Patients undergoing SRS for AVM were enrolled prospectively. 4D flow MRI was performed prior to SRS and 6 months post-treatment. <i>Imaging:</i> Imaging was performed on a 3T scanner with dedicated head coil. 4D flow sequences were based on a 3D spoiled gradient echo sequence. Three directional velocity encoding gradients were used with Venc 100-200 cm/s. Additional MRI sequences were obtained to identify the nidus and feeding arteries. <i>Flow Analysis:</i> In each case the dominant feeding artery was identified. Mean blood flow over the cardiac cycle was measured in a proximal segment of the feeding artery. Blood flow was measured in the same location both before and 6 months after SRS. Blood flow was measured using software with FDA clearance for clinical 4D flow post-processing. Response was defined as fractional arterial blood flow after treatment vs. before treatment. <i>Statistical Analysis:</i> We defined the cut-off between ‘responders' and ‘non-responders' as the median blood flow response. Survival analysis was performed to assess the relationship between binarized blood flow response and nidus obliteration, with bleeding or death prior to obliteration treated as competing risks. Gray's test was used to assess for equality in the cumulative incidence functions for obliteration or bleeding/death between responders and non-responders. <h3>Results</h3> 18 subjects have completed pre- and post-treatment imaging. Median time to post-treatment imaging was 179 Days (IQR 169-202 Days). Median response was 0.52 (IQR 0.44-0.84). Median follow up is 755 Days (IQR 438-1188 Days). There have been no deaths. Amongst responders, there have been 4 obliteration events and 0 bleeding events. Amongst non-responders there have been 0 obliteration events and 2 bleeding events. There is a trend toward an increase in cumulative incidence of obliteration amongst responders (p=0.08) and in bleeding amongst non-responders (p=0.11). <h3>Conclusion</h3> Preliminary results suggest 4D flow MRI may be an early predictor of clinical outcomes after AVM SRS. Further follow up with additional events will be required to confirm a predictive relationship and to determine an optimal cutoff for distinguishing responders from non-responders.

Highly Accelerated Compressed-Sensing 4D Flow for Intracardiac Flow Assessment.

Four-dimensional (4D) flow MRI allows for the quantification of complex flow patterns; however, its clinical use is limited by its inherently long acquisition time. Compressed sensing (CS) is an acceleration technique that provides substantial reduction in acquisition time. To compare intracardiac flow measurements between conventional and CS-based highly accelerated 4D flow acquisitions. Prospective. Fifty healthy volunteers (28.0 ± 7.1 years, 24 males). Whole heart time-resolved 3D gradient echo with three-directional velocity encoding (4D flow) with conventional parallel imaging (factor 3) as well as CS (factor 7.7) acceleration at 3T. 4D flow MRI data were postprocessed by applying a valve tracking algorithm. Acquisition times, flow volumes (mL/cycle) and diastolic function parameters (ratio of early to late diastolic left ventricular peak velocities [E/A] and ratio of early mitral inflow velocity to mitral annular early diastolic velocity [E/e']) were quantified by two readers. Paired-samples t-test and Wilcoxon rank sum test to compare measurements. Pearson correlation coefficient (r), Bland-Altman-analysis (BA) and intraclass correlation coefficient (ICC) to evaluate agreement between techniques and readers. A P value < 0.05 was considered statistically significant. A significant improvement in acquisition time was observed using CS vs. conventional accelerated acquisition (6.7 ± 1.3 vs. 12.0 ± 1.3min). Net forward flow measurements for all valves showed good correlation (r > 0.81) and agreement (ICCs > 0.89) between conventional and CS acceleration, with 3.3%-8.3% underestimation by the CS technique. Evaluation of diastolic function showed 3.2%-17.6% error: E/A 2.2 [1.9-2.4] (conventional) vs. 2.3 [2.0-2.6] (CS), BA bias 0.08 [-0.81-0.96], ICC 0.82; and E/e' 4.6 [3.9-5.4] (conventional) vs. 3.8 [3.4-4.3] (CS), BA bias -0.90 [-2.31-0.50], ICC 0.89. Analysis of intracardiac flow patterns and evaluation of diastolic function using a highly accelerated 4D flow sequence prototype is feasible, but it shows underestimation of flow measurements by approximately 10%. 2 TECHNICAL EFFICACY: Stage 1.

Time-resolved velocity mapping at high magnetic fields: A preclinical comparison between stack‐of‐stars and cartesian 4D-Flow

Purpose: Prospectively-gated Cartesian 4D-flow (referred to as Cartesian-4D-flow) imaging suffers from long TE and intensified flow-related intravoxel-dephasing especially in preclinical ultra-high field MRI. The ultra-short-echo (UTE) 4D-flow technique can resolve the signal loss in higher-order blood flows; however, the long scan time of the high resolution UTE-4D-flow is considered as a disadvantage for preclinical imaging. To compensate for prolonged acquisitions, an accelerated k0-navigated golden-angle center-out stack-of-stars 4D-flow sequence (referred to as SoS-4D-flow) was implemented at 9.4T and the results were compared to conventional Cartesian-4D-flow mapping in-vitro and in-vivo.Methods: The study was conducted in three steps (A) In-vitro evaluation in a static phantom: to quantify the background velocity bias. (B) In-vitro evaluation in a flowing water phantom: to investigate the effects of polar undersampling (US) on the measured velocities and to compare the spatial velocity profiles between both sequences. (C) In-vivo evaluations: 24 C57BL/6 mice were measured by SoS-4D-flow (n = 14) and Cartesian-4D-flow (n = 10). The peak systolic velocity in the ascending aorta and the background velocity in the anterior chest wall were analyzed for both techniques and were compared to each other.Results: According to the in-vitro analysis, the background velocity bias was significantly lower in SoS-4D-flow than in Cartesian-4D-flow (p &amp;lt; 0.05). Polar US in SoS-4D-flow influenced neither the measured velocity values nor the spatial velocity profiles in comparison to Cartesian-4D-flow. The in-vivo analysis showed significantly higher diastolic velocities in Cartesian-4D-flow than in SoS-4D-flow (p &amp;lt; 0.05). A systemic background bias was observed in the Cartesian velocity maps which influenced their streamline directions and magnitudes.Conclusion: The results of our study showed that at 9.4T SoS-4D-flow provided higher accuracy in slow flow imaging than Cartesian-4D-flow, while the same measurement time could be achieved.

Assessment of hepatic arterial hemodynamics with 4D flow MRI: in vitro analysis of motion and spatial resolution related error and in vivo feasibility study in 20 volunteers.

To assess the ability of four-dimensional (4D) flow MRI to measure hepatic arterial hemodynamics by determining the effects of spatial resolution and respiratory motion suppression in vitro and its applicability in vivo with comparison to two-dimensional (2D) phase-contrast MRI. A dynamic hepatic artery phantom and 20 consecutive volunteers were scanned. The accuracies of Cartesian 4D flow sequences with k-space reordering and navigator gating at four spatial resolutions (0.5- to 1-mm isotropic) and navigator acceptance windows (± 8 to ± 2 mm) and one 2D phase-contrast sequence (0.5-mm in -plane) were assessed in vitro at 3 T. Two sequences centered on gastroduodenal and hepatic artery branches were assessedin vivo for intra - and interobserver agreement and compared to 2D phase-contrast. In vitro, higher spatial resolution led to a greater decrease in error than narrower navigator window (30.5 to -4.67% vs -6.64 to -4.67% for flow). In vivo, hepatic and gastroduodenal arteries were more often visualized with the higher resolution sequence (90 vs 71%). Despite similar interobserver agreement (κ = 0.660 and 0.704), the higher resolution sequence had lower variability for area (CV = 20.04 vs 30.67%), flow (CV = 34.92 vs 51.99%), and average velocity (CV = 26.47 vs 44.76%). 4D flow had lower differences between inflow and outflow at the hepatic artery bifurcation (11.03 ± 5.05% and 15.69 ± 6.14%) than 2D phase-contrast (28.77 ± 21.01%). High-resolution 4D flow can assess hepatic artery anatomy and hemodynamics with improved accuracy, greater vessel visibility, better interobserver reliability, and internal consistency. • Motion-suppressed Cartesian four-dimensional (4D) flow MRI with higher spatial resolution provides more accurate measurements even when accepted respiratory motion exceeds voxel size. • 4D flow MRI with higher spatial resolution provides substantial interobserver agreement for visualization of hepatic artery branches. • Lower peak and average velocities and a trend toward better internal consistency were observed with 4D flow MRI as compared to 2D phase-contrast.

Characteristics of Right Ventricular Blood Flow in Patients With Chronic Thromboembolic Pulmonary Hypertension: An Analysis With 4-Dimensional Flow Cardiovascular Magnetic Resonance Imaging.

BackgroundBlood flow is closely related to function, but currently, the relationship of right ventricular (RV) blood flow components with RV function and hemodynamics in patients with chronic thromboembolic pulmonary hypertension (CTEPH) remains unclear. Our objective is to qualify RV function with 4-dimensional flow cardiovascular magnetic resonance (4D-Flow CMR) imaging and to investigate the correlation between RV flow and hemodynamics in patients with CTEPH.MethodsRetrospective enrollment included 67 patients with CTEPH (mean age 47.8±14.2 years, 47 men) who underwent CMR and right heart catheterization (RHC) within 2 days. RHC was used to evaluate hemodynamics. RV flow components including the percentages of direct flow (PDF), retained inflow (PRI), delayed ejection flow (PDEF), and residual volume (PRVo) were quantified on 4D-Flow sequence. RV functional metrics were determined with the CINE balanced steady-state free precession sequence. The sum of PDF and PDEF was compared with RV eject fraction (RVEF). The correlation among RV flow components, RV functional metrics and hemodynamics was analyzed with spearman correlation analysis.ResultsThe median (interquartile range) of RVEF, PDF, PDEF, PRI, and PRVo, respectively was 35.5% (18.2, 45.6%), 18% (8.4, 21.4%), 15.1% (13.5, 19.0%), 15.9% (13.8, 20.8%), and 50.6% (35.6, 60.4%). The sum of PDF and PDEF is 35.1% (24.8, 46.6%), which was similar to RVEF (z = 0.58, p = 0.561). PDF negatively correlated with right ventricular end-systolic volume index (RVESVI), right ventricular myocardial mass index (RVMI) and right ventricular global longitudinal strain (r = −0.61, −0.65, −0.64, p < 0.001). PRVo positively correlated with RVESVI and RVMI (r = 0.50, 0.58, p < 0.001). PDF negatively correlated with pulmonary vascular resistance (PVR) (r = −0.72, p < 0.001) while it positively correlated with cardiac output (CO) and cardiac index (CI) (r = 0.64 & 0.52, p < 0.001). PRVo positively correlated with mean pulmonary pressure and PVR (r = 0.57&0.54, p < 0.001). Total five patients died in the perioperative period. RVEF in the deceased patients was similar to survivors (z = −1.163, p = 0.092). In comparison with the survivors, RVPDF in the deceased patients significantly reduced (z = −2.158, p = 0.029) while RVPDEF, RVPRI, and RVPRVo in deceased patients were similar to survivors.Conclusion4D-Flow CMR can provide simultaneous quantification of RV function and hemodynamics in the assessment of CTEPH without breath-holding. The reduced PDF and increased PRVo were the main characteristics of RV flow in CTEPH.

Vortex formation time as an index of left ventricular filling efficiency: comparison between children volunteers and patients with tetralogy of Fallot.

BackgroundVortex formation time (VFT) had been considered a useful marker for assessing diastolic performance. the VFT assessment of diastolic function using four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has not been used in repair of tetralogy of Fallot (rTOF) patient. The aims of this study were as follows: (I) establish reference ranges for VFT measurements in healthy children and adolescents using 4D flow CMR imaging; and (II) analyze VFT parameters to assess diastole dysfunction in rTOF patients group.MethodsWe acquired the CMR data was of 62 healthy participants (aged 6–18 years; male: 40, female: 22) and 20 patients with rTOF (aged 10–13 years; male: 15, female: 5) using 4D flow and cine sequence in routine chamber view. The VFT was calculated based on comparison of different algorithms from cine measurements (VFTvolume) and 4D flow measurements (VFTblood). Then, VFT measurements were compared to subject peak filling rate (PFR), age, and cardiac mass using simple linear regression and multiple regression analyses. Data were also categorized according to age for VFT and cardiac functional assessment comparisons between 3 age groups (Group 1: 6–9 years; Group 2: 10–13 years; Group 3: 14–18 years). The correlation of VFT and cardiac function parameters were analyzed in the rTOF group.ResultsNormal mean value of VFTvolume and VFTblood were 4.25±0.92 and 3.77±1.11 in healthy children participants. The VFTvolume was correlated with VFTblood (r=0.61, P<0.001). There was a moderately significant correlation between VFTvolume and PFR (r=0.46, P<0.001) and between VFTblood and PFR (r=0.47, P<0.001), age (r=0.41, P=0.002) and left ventricular (LV) mass (r=0.48, P<0.001). Multiple regression analyses demonstrated that VFTvolume was independently associated with PFR (T=2.239; P<0.05) and VFTblood (T=4.361; P<0.001). There was a significant difference in VFTvolume between healthy controls and rTOF patients (5.44±1.93 vs. 4.27±0.88, P=0.018).ConclusionsThe VFT measurements showed that the LV that had appropriate space to form the optimal vortex ring in normal children and adolescents aged 6–18 years old. The VFTvolume could potentially be helpful in improving our understanding of LV diastolic dysfunction in rTOF patients.

Longitudinal Changes in Left Ventricular Blood Flow Kinetic Energy After Myocardial Infarction: Predictive Relevance for Cardiac Remodeling.

Four-dimensional (4D) flow cardiac magnetic resonance (cardiac MR) imaging provides quantification of intracavity left ventricular (LV) flow kinetic energy (KE) parameters in three dimensions. ST-elevation myocardial infarction (STEMI) patients have been shown to have altered intracardiac blood flow compared to controls; however, how 4D flow parameters change over time has not been explored previously. Measure longitudinal changes in intraventricular flow post-STEMI and ascertain its predictive relevance of long-term cardiac remodeling. Prospective. Thirty-five STEMI patients (M:F = 26:9, aged 56 ± 9 years). A 3 T/3D EPI-based, fast field echo (FFE) free-breathing 4D-flow sequence with retrospective cardiac gating. Serial imaging at 3-7 days (V1), 3-months (V2), and 12-months (V3) post-STEMI, including the following protocol: functional imaging for measuring volumes and 4D-flow for calculating parameters including systolic and peakE-wave LVKE, normalized to end-diastolic volume (iEDV) and stroke volume (iSV). Data were analyzed by H.B. (3 years experience). Patients were categorized into two groups: preserved ejection fraction (pEF, if EF > 50%) and reduced EF (rEF, if EF < 50%). Independent sample t-tests were used to detect the statistical significance between any two cohorts. P < 0.05 was considered statistically significant. Across the cohort, systolic KEisv was highest at V1 (28.0 ± 4.4μJ/mL). Patients with rEF retained significantly higher systolic KEisv than patients with pEF at V2 (18.2 ± 3.4μJ/mL vs. 6.9 ± 0.6μJ/mL, P < 0.001) and V3 (21.6 ± 5.1μJ/mL vs. 7.4 ± 0.9μJ/mL, P < 0.001). Patients with pEF had significantly higher peakE-wave KEiEDV than rEF patients throughout the study (V1: 25.4 ± 11.6μJ/mL vs. 18.1 ± 9.9μJ/mL, P < 0.03, V2: 24.0 ± 10.2μJ/mL vs. 17.2 ± 12.2μJ/mL, P < 0.05, V3: 27.7 ± 14.8μJ/mL vs. 15.8 ± 7.6μJ/mL, P < 0.04). Systolic KE increased acutely following MI; in patients with pEF, this decreased over 12months, while patients with rEF, this remained raised. Compared to patients with pEF, persistently lower peakE-wave KE in rEF patients is suggestive of early and fixed impairment in diastolic function. 1 TECHNICAL EFFICACY: Stage 3.

Hemodynamic Assessment of Structural Heart Disease Using 4D Flow MRI: How We Do It.

MRI is an essential diagnostic tool in the anatomic and functional evaluation of cardiovascular disease. In many practices, 2D phase-contrast (2D-PC) MRI has been used for blood flow quantification. Four-dimensional flow MRI is a time-resolved volumetric acquisition that captures the vector field of blood flow along with anatomic images. It also provides a simpler acquisition compared with 2D-PC and facilitates a more accurate and comprehensive hemodynamic assessment. Advancements in accelerated imaging have significantly shortened scanning times for 4D flow MRI while preserving image quality, enabling this technology to transition from the research arena to routine clinical practice. In this article, we review technical optimization based on our more than 10 years of clinical experience with 4D flow MRI. We also present pearls and pitfalls in the practical application of 4D flow MRI, including how to quantify cardiovascular shunts, valvular or vascular stenosis, and valvular regurgitation. As experience increases, and as 4D flow sequences and postprocessing software become more broadly available, 4D flow MRI will likely become an essential component of cardiac imaging in practices involved in the management of congenital and acquired structural heart disease.