Comprehensive sex-specific and age-dependent analysis of four-dimensional flow cardiovascular magnetic resonance assessed aortic blood flow-related parameters in normal subjects using single-vendor magnetic resonance systems and single-vendor software.

Aortic blood flow characterization by four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) is increasingly performed in aneurysm research. A limited number of studies have established normal values that can aid the recognition of abnormal flow at an early stage. This study aims to establish additional sex-specific and age-dependent reference values for flow-related parameters in a large cohort of healthy adults. Two hundred and twelve volunteers were included, and 191 volunteers completed the full study protocol. All underwent 4D flow CMR of the entire aorta. Quantitative values for velocity, vorticity, helicity, as well as total, circumferential, and axial wall shear stress (WSS) were determined for the aortic root (AoR), ascending aorta (AAo), aortic arch, descending aorta (DAo), suprarenal aorta, and infrarenal aorta. Vorticity and helicity were indexed for segment volume (mL). The normal values were estimated per sex and age group, where significant differences between males (M) and females (F) were found only for specific age groups. More specifically, the following variables were significantly different after applying the false discovery rate correction for multiple testing: 1) velocity in the AAo and DAo in the 60-70 years age group (mean ± SD: (M) 47.0 ± 8.2 cm s-1 vs (F) 38.4 ± 6.9 cm s-1, p = 0.001 and, (M) 55.9 ± 9.9 cm s-1 vs (F) 46.5 ± 5.5 cm s-1, p = 0.002), 2) normalized vorticity in AoR in the 50-59 years age group ((M) 27,539 ± 5042 s-1 mL-1 vs (F) 30,849 ± 7285 s-1 mL-1, p = 0.002), 3) axial WSS in the Aao in the 18-29 age group ((M) 1098 ± 203 mPa vs (F) 921 ± 121 mPa, p = 0.002). Good to strong negative correlations with age were seen for almost all variables, in different segments, and for both sexes. This study describes reference values for aortic flow-related parameters acquired by 4D flow MRI. We observed limited differences between males and females. A negative relationship with age was seen for almost all flow-related parameters and segments.

Ramaekers MJFG ，Te Kiefte BJC ，Adriaans BP ，Juffermans JF ，van Assen HC ，Winkens B ，Wildberger JE ，Lamb HJ ，Schalla S ，Westenberg JJM ... -  《-》

Assessment of abnormal transvalvular flow and wall shear stress direction for pediatric/young adults with bicuspid aortic valve: A cross-sectional four-dimensional flow study.

Aortic dilation is seen in pediatric/young adult patients with bicuspid aortic valve (BAV), and hemodynamic markers to predict aortic dilation are necessary for monitoring. Although promising hemodynamic metrics, such as abnormal wall shear stress (WSS) magnitude, have been proposed for adult BAV patients using four-dimensional (4D) flow cardiovascular magnetic resonance, those for pediatric BAV patients have less frequently been reported, partly due to scarcity of data to define normal WSS range. To circumvent this challenge, this study aims to investigate if a recently proposed 4D flow-based hemodynamic measurement, abnormal flow directionality, is associated with aortic dilation in pediatric/young adult BAV patients. 4D flow scans for BAV patients (<20 years old) and age-matched controls were retrospectively enrolled. Static segmentation for the aorta and pulmonary arteries was obtained to quantify peak systolic hemodynamics and diameters in the proximal aorta. In addition to peak velocity, WSS, vorticity, helicity, and viscous energy loss, direction of aortic velocity and WSS in BAV patients were compared with that of control atlas using registration technique; angle differences of >60 deg and >120 deg were defined as moderately and severely abnormal, respectively. The association between the obtained metrics and normalized diameters (Z-scores) was evaluated at the sinotubular junction, mid-ascending aorta, and distal ascending aorta. Fifty-three BAV patients, including 18 with history of repaired aortic coarctation, and 17 controls were enrolled. Correlation between moderately abnormal velocity/WSS direction and aortic Z-scores was moderate to strong at the sinotubular junction and mid-ascending aorta (R = 0.62-0.81; p < 0.001) while conventional measurements exhibited weaker correlation (|R| = 0.003-0.47, p = 0.009-0.99) in all subdomains. Multivariable regression analysis found moderately abnormal velocity direction and existence of aortic regurgitation (only for isolated BAV group) were independently associated with mid-ascending aortic Z-scores. Abnormal velocity and WSS directionality in the proximal aorta were strongly associated with aortic Z-scores in pediatric/young adult BAV patients.

Fujiwara T ，Malone LJ ，Chatfield KC ，Berthusen A ，Fonseca B ，Browne LP ，Barker AJ ... -  《-》

Four-dimensional flow cardiovascular magnetic resonance aortic cross-sectional pressure changes and their associations with flow patterns in health and ascending thoracic aortic aneurysm.

Ascending thoracic aortic aneurysm (ATAA) is a silent and threatening dilation of the ascending aorta (AscAo). Maximal aortic diameter which is currently used for ATAA patients management and surgery planning has been shown to inadequately characterize risk of dissection in a large proportion of patients. Our aim was to propose a comprehensive quantitative evaluation of aortic morphology and pressure-flow-wall associations from four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) data in healthy aging and in patients with ATAA. We studied 17 ATAA patients (64.7 ± 14.3 years, 5 females) along with 17 age- and sex-matched healthy controls (59.7 ± 13.3 years, 5 females) and 13 younger healthy subjects (33.5 ± 11.1 years, 4 females). All subjects underwent a CMR exam, including 4D flow and three-dimensional anatomical images of the aorta. This latter dataset was used for aortic morphology measurements, including AscAo maximal diameter (iDMAX) and volume, indexed to body surface area. 4D flow MRI data were used to estimate 1) cross-sectional local AscAo spatial (∆PS) and temporal (∆PT) pressure changes as well as the distance (∆DPS) and time duration (∆TPT) between local pressure peaks, 2) AscAo maximal wall shear stress (WSSMAX) at peak systole, and 3) AscAo flow vorticity amplitude (VMAX), duration (VFWHM), and eccentricity (VECC). Consistency of flow and pressure indices was demonstrated through their significant associations with AscAo iDMAX (WSSMAX:r = -0.49, p < 0.001; VECC:r = -0.29, p = 0.045; VFWHM:r = 0.48, p < 0.001; ∆DPS:r = 0.37, p = 0.010; ∆TPT:r = -0.52, p < 0.001) and indexed volume (WSSMAX:r = -0.63, VECC:r = -0.51, VFWHM:r = 0.53, ∆DPS:r = 0.54, ∆TPT:r = -0.63, p < 0.001 for all). Intra-AscAo cross-sectional pressure difference, ∆PS, was significantly and positively associated with both VMAX (r = 0.55, p = 0.002) and WSSMAX (r = 0.59, p < 0.001) in the 30 healthy subjects (48.3 ± 18.0 years). Associations remained significant after adjustment for iDMAX, age, and systolic blood pressure. Superimposition of ATAA patients to normal aging trends between ∆PS and WSSMAX as well as VMAX allowed identifying patients with substantially high pressure differences concomitant with AscAo dilation. Local variations in pressures within ascending aortic cross-sections derived from 4D flow MRI were associated with flow changes, as quantified by vorticity, and with stress exerted by blood on the aortic wall, as quantified by wall shear stress. Such flow-wall and pressure interactions might help for the identification of at-risk patients.

Bouaou K ，Dietenbeck T ，Soulat G ，Bargiotas I ，Houriez-Gombaud-Saintonge S ，De Cesare A ，Gencer U ，Giron A ，Jiménez E ，Messas E ，Lucor D ，Bollache E ，Mousseaux E ，Kachenoura N ... -  《-》

Combined free-running four-dimensional anatomical and flow magnetic resonance imaging with native contrast using Synchronization of Neighboring Acquisitions by Physiological Signals.

Four-dimensional (4D) flow magnetic resonance imaging (MRI) often relies on the injection of gadolinium- or iron-oxide-based contrast agents to improve vessel delineation. In this work, a novel technique is developed to acquire and reconstruct 4D flow data with excellent dynamic visualization of blood vessels but without the need for contrast injection. Synchronization of Neighboring Acquisitions by Physiological Signals (SyNAPS) uses pilot tone (PT) navigation to retrospectively synchronize the reconstruction of two free-running three-dimensional radial acquisitions, to create co-registered anatomy and flow images. Thirteen volunteers and two Marfan syndrome patients were scanned without contrast agent using one free-running fast interrupted steady-state (FISS) sequence and one free-running phase-contrast MRI (PC-MRI) sequence. PT signals spanning the two sequences were recorded for retrospective respiratory motion correction and cardiac binning. The magnitude and phase images reconstructed, respectively, from FISS and PC-MRI, were synchronized to create SyNAPS 4D flow datasets. Conventional two-dimensional (2D) flow data were acquired for reference in ascending (AAo) and descending aorta (DAo). The blood-to-myocardium contrast ratio, dynamic vessel area, net volume, and peak flow were used to compare SyNAPS 4D flow with Native 4D flow (without FISS information) and 2D flow. A score of 0-4 was given to each dataset by two blinded experts regarding the feasibility of performing vessel delineation. Blood-to-myocardium contrast ratio for SyNAPS 4D flow magnitude images (1.5 ± 0.3) was significantly higher than for Native 4D flow (0.7 ± 0.1, p < 0.01) and was comparable to 2D flow (2.3 ± 0.9, p = 0.02). Image quality scores of SyNAPS 4D flow from the experts (M.P.: 1.9 ± 0.3, E.T.: 2.5 ± 0.5) were overall significantly higher than the scores from Native 4D flow (M.P.: 1.6 ± 0.6, p = 0.03, E.T.: 0.8 ± 0.4, p < 0.01) but still significantly lower than the scores from the reference 2D flow datasets (M.P.: 2.8 ± 0.4, p < 0.01, E.T.: 3.5 ± 0.7, p < 0.01). The Pearson correlation coefficient between the dynamic vessel area measured on SyNAPS 4D flow and that from 2D flow was 0.69 ± 0.24 for the AAo and 0.83 ± 0.10 for the DAo, whereas the Pearson correlation between Native 4D flow and 2D flow measurements was 0.12 ± 0.48 for the AAo and 0.08 ± 0.39 for the DAo. Linear correlations between SyNAPS 4D flow and 2D flow measurements of net volume (r2 = 0.83) and peak flow (r2 = 0.87) were larger than the correlations between Native 4D flow and 2D flow measurements of net volume (r2 = 0.79) and peak flow (r2 = 0.76). The feasibility and utility of SyNAPS were demonstrated for joint whole-heart anatomical and flow MRI without requiring electrocardiography gating, respiratory navigators, or contrast agents. Using SyNAPS, a high-contrast anatomical imaging sequence can be used to improve 4D flow measurements that often suffer from poor delineation of vessel boundaries in the absence of contrast agents.

Falcão MBL ，Mackowiak ALC ，Rossi GMC ，Prša M ，Tenisch E ，Rumac S ，Bacher M ，Rutz T ，van Heeswijk RB ，Speier P ，Markl M ，Bastiaansen JAM ，Stuber M ，Roy CW ... -  《-》

Regional aortic wall shear stress increases over time in patients with a bicuspid aortic valve.

Aortic wall shear stress (WSS) is a known predictor of ascending aortic growth in patients with a bicuspid aortic valve (BAV). The aim of this study was to study regional WSS and changes over time in BAV patients. BAV patients and age-matched healthy controls underwent four-dimensional (4D) flow cardiovascular magnetic resonance (CMR). Regional, peak systolic ascending aortic WSS, aortic valve function, aortic stiffness measures, and aortic dimensions were assessed. In BAV patients, 4D flow CMR was repeated after 3 years of follow-up and both at baseline and follow-up computed tomography angiography (CTA) were acquired. Aortic growth (volume increase of ≥5%) was measured on CTA. Regional WSS differences within patients' aorta and WSS changes over time were analyzed using linear mixed-effect models and were associated with clinical parameters. Thirty BAV patients (aged 34 years [interquartile range (IQR) 25-41]) were included in the follow-up analysis. Additionally, another 16 BAV patients and 32 healthy controls (aged 33 years [IQR 28-48]) were included for other regional analyses. Magnitude, axial, and circumferential WSS increased over time (all p < 0.001) irrespective of aortic growth. The percentage of regions exposed to a magnitude WSS >95th percentile of healthy controls increased from 21% (baseline 506/2400 regions) to 31% (follow-up 734/2400 regions) (p < 0.001). WSS angle, a measure of helicity near the aortic wall, decreased during follow-up. Magnitude WSS changes over time were associated with systolic blood pressure, peak aortic valve velocity, aortic valve regurgitation fraction, aortic stiffness indexes, and normalized flow displacement (all p < 0.05). An increase in regional WSS over time was observed in BAV patients, irrespective of aortic growth. The increasing WSSs, comprising a larger area of the aorta, warrant further research to investigate the possible predictive value for aortic dissection.

Minderhoud SCS ，Arrouby A ，van den Hoven AT ，Bons LR ，Chelu RG ，Kardys I ，Rizopoulos D ，Korteland SA ，van den Bosch AE ，Budde RPJ ，Roos-Hesselink JW ，Wentzel JJ ，Hirsch A ... -  《-》