Flow MRI Research Articles

High-Frame-Rate Ultrasound Velocimetry in the Healthy Femoral Bifurcation: A Comparative Study Against 4-D Flow Magnetic Resonance Imaging

ObjectiveLocal flow dynamics impact atherosclerosis yet are difficult to quantify with conventional ultrasound techniques. This study investigates the performance of ultrasound vector flow imaging (US-VFI) with and without ultrasound contrast agents in the healthy femoral bifurcation. MethodsHigh-frame-rate ultrasound data with incremental acoustic outputs were acquired in the femoral bifurcations of 20 healthy subjects before (50V) and after contrast injection (2V, 5V and 10V). 2-D blood-velocity profiles were obtained through native blood speckle tracking (BST) and contrast tracking (echo particle image velocimetry [echoPIV]). As a reference, 4-D flow magnetic resonance imaging (4-D flow MRI) was acquired. Contrast-to-background ratio and vector correlation were used to assess the quality of the US-VFI acquisitions. Spatiotemporal velocity profiles were extracted, from which peak velocities (PSV) were compared between the modalities. Furthermore, root-mean-square error analysis was performed. ResultsUS-VFI was successful in 99% of the cases and optimal VFI quality was established with the 10V echoPIV and BST settings. A good correspondence between 10V echoPIV and BST was found, with a mean PSV difference of -0.5 cm/s (limits of agreement: -14.1–13.2). Both US-VFI techniques compared well with 4-D flow MRI, with a mean PSV difference of 1.4 cm/s (-18.7–21.6) between 10V echoPIV and MRI, and 0.3 cm/s (-23.8–24.4) between BST and MRI. Similar complex flow patterns among all modalities were observed. Conclusion2-D blood-flow quantification of femoral bifurcation is feasible with echoPIV and BST. Both modalities showed good agreement compared to 4-D flow MRI. For the femoral tract the administration of contrast was not needed to increase the echogenicity of the blood for optimal image quality.

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.

In vitro and in silico assessment of flow modulation after deploying the Contour Neurovascular System in intracranial aneurysm models

BackgroundThe novel Contour Neurovascular System (Contour) has been reported to be efficient and safe for the treatment of intracranial, wide-necked bifurcation aneurysms. Flow in the aneurysm and posterior cerebral arteries...

Imaging and Hemodynamic Characteristics of Vulnerable Carotid Plaques and Artificial Intelligence Applications in Plaque Classification and Segmentation.

Stroke is a massive public health problem. The rupture of vulnerable carotid atherosclerotic plaques is the most common cause of acute ischemic stroke (AIS) across the world. Currently, vessel wall high-resolution magnetic resonance imaging (VW-HRMRI) is the most appropriate and cost-effective imaging technique to characterize carotid plaque vulnerability and plays an important role in promoting early diagnosis and guiding aggressive clinical therapy to reduce the risk of plaque rupture and AIS. In recent years, great progress has been made in imaging research on vulnerable carotid plaques. This review summarizes developments in the imaging and hemodynamic characteristics of vulnerable carotid plaques on the basis of VW-HRMRI and four-dimensional (4D) flow MRI, and it discusses the relationship between these characteristics and ischemic stroke. In addition, the applications of artificial intelligence in plaque classification and segmentation are reviewed.

Characterizing pore-scale structure-flow correlations in sedimentary rocks using magnetic resonance imaging.

Quantitative, three-dimensional (3D) spatially resolved magnetic resonance flow imaging (flow MRI) methods are presented to characterize structure-flow correlations in a 4-mm-diameter plug of Ketton limestone rock using undersampled k- and q-space data acquisition methods combined with compressed sensing (CS) data reconstruction techniques. The acquired MRI data are coregistered with an X-ray microcomputed tomography (μCT) image of the same rock sample, allowing direct correlation of the structural features of the rock with local fluid transport characteristics. First, 3D velocity maps acquired at 35 μm isotropic spatial resolution showed that the flow was highly heterogeneous, with ∼10% of the pores carrying more than 50% of the flow. Structure-flow correlations were found between the local flow velocities through pores and the size and topology (coordination number) associated with these pores. These data show consistent trends with analogous data acquired for flow through a packing of 4-mm-diameter spheres, which may be due to the microstructure of Ketton rock being a consolidation of approximately spherical grains. Using two-dimensional and 3D visualization of coregistered μCT images and velocity maps, complex pore-scale flow patterns were identified. Second, 3D spatially resolved propagators were acquired at 94 μm isotropic spatial resolution. Flow dispersion within the rock was examined by analyzing each of the 331 776 local propagators as a function of observation time. Again, the heterogeneity of flow within the rock was shown. Quantification of the mean and standard deviation of each of the local propagators showed enhanced mixing occurring within the pore space at longer observation times. These spatially resolved measurements also enable investigation of the length scale of a representative elementary volume. It is shown that for a 4-mm-diameter plug this length scale is not reached.

Aortic and mitral flow quantification using dynamic valve tracking and machine learning: Prospective study assessing static and dynamic plane repeatability, variability and agreement.

BackgroundBlood flow is a crucial measurement in the assessment of heart valve disease. Time-resolved flow using magnetic resonance imaging (4 D flow MRI) can provide a comprehensive assessment of heart valve hemodynamics but it relies in manual plane analysis. In this study, we aimed to demonstrate the feasibility of automate the detection and tracking of aortic and mitral valve planes to assess blood flow from 4 D flow MRI.MethodsIn this prospective study, a total of n = 106 subjects were enrolled: 19 patients with mitral disease, 65 aortic disease patients and 22 healthy controls. Machine learning was employed to detect aortic and mitral location and motion in a cine three-chamber plane and a perpendicular projection was co-registered to the 4 D flow MRI dataset to quantify flow volume, regurgitant fraction, and a peak velocity. Static and dynamic plane association and agreement were evaluated. Intra- and inter-observer, and scan-rescan reproducibility were also assessed.ResultsAortic regurgitant fraction was elevated in aortic valve disease patients as compared with controls and mitral valve disease patients (p < 0.05). Similarly, mitral regurgitant fraction was higher in mitral valve patients (p < 0.05). Both aortic and mitral total flow were high in aortic patients. Static and dynamic were good (r > 0.6, p < 0.005) for aortic total flow and peak velocity, and mitral peak velocity and regurgitant fraction. All measurements showed good inter- and intra-observer, and scan-rescan reproducibility.ConclusionWe demonstrated that aortic and mitral hemodynamics can efficiently be quantified from 4 D flow MRI using assisted valve detection with machine learning.

Additional value and new insights by four-dimensional flow magnetic resonance imaging in congenital heart disease: application in neonates and young children

Cardiovascular MRI has become an essential imaging modality in children with congenital heart disease (CHD) in the last 15–20 years. With use of appropriate sequences, it provides important information on cardiovascular anatomy, blood flow and function for initial diagnosis and post-surgical or -interventional monitoring in children. Although considered as more sophisticated and challenging than CT, in particular in neonates and infants, MRI is able to provide information on intra- and extracardiac haemodynamics, in contrast to CT. In recent years, four-dimensional (4-D) flow MRI has emerged as an additional MR technique for retrospective assessment and visualisation of blood flow within the heart and any vessel of interest within the acquired three-dimensional (3-D) volume. Its application in young children requires special adaptations for the smaller vessel size and faster heart rate compared to adolescents or adults. In this article, we provide an overview of 4-D flow MRI in various types of complex CHD in neonates and infants to demonstrate its potential indications and beneficial application for optimised individual cardiovascular assessment. We focus on its application in clinical routine cardiovascular workup and, in addition, show some examples with pathologies other than CHD to highlight that 4-D flow MRI yields new insights in disease understanding and therapy planning. We shortly review the essentials of 4-D flow data acquisition, pre- and post-processing techniques in neonates, infants and young children. Finally, we conclude with some details on accuracy, limitations and pitfalls of the technique.

CO2 cerebrovascular reactivity measured with phase‐contrast MRI: A potential biomarker of cognition and physical function in older adults

AbstractBackgroundVascular cognitive decline is a prominent cause of late‐life cognitive impairment. Compared to Alzheimer’s disease(AD), there is a paucity of biomarkers for its diagnosis, stratification, and treatment monitoring. Cerebrovascular‐Reactivity(CVR) MRI measures small‐vessel dilation to vasoactive‐stimuli(e.g. CO2), and has been shown to be associated with cognitive impairment. However, previous CVR studies were based on Blood‐Oxygenation‐Level‐Dependent (BOLD) MRI signal, which reflects a complex interplay of many physiological parameters and thus presents interpretation challenges. We measured CVR using quantitative CBF‐imaging in older participants, and tested for associations with diagnosis (Healthy Control [HC] vs. mild‐cognitive‐impairment [MCI] vs. dementia) cognitive and physical function, amyloid and tau burden, and vascular risk.MethodsA cross‐sectional study enrolled 67 participants aged 69±6.5 years (22 HC, 37 MCI, 8 dementia). MoCA (Montreal‐Cognitive‐Assessment) and composite cognition (a z‐score average of 4‐domains: verbal‐memory, executive‐function, language, processing‐speed) assessed overall cognition. Gait(sec,4‐meter‐walk) and chair‐stands (sec,5‐chair‐stands) assessed physical‐function. Clinical Dementia Rating(CDR)7 indexed disease‐severity. Phase‐contrast flow MRI(3T) was performed while participants breathed room‐air for 1‐minute, followed by ‘CO2‐enriched‐air’(5%CO2, 21%O2, 74%N2) for 2‐minutes. Blood‐flux at Superior‐Sagittal‐Sinus(SSS)(Figure‐1) was quantified for both states. Breathing rate and End‐tidal(Et)‐CO2 were recorded via capnography. CBF‐based CVR was then obtained by: CBF‐CVR = [HypercapniaSSSflux(ml/min)‐RoomairSSSflux(ml/min)]/RoomairSSSflux(ml/min) HypercapniaEtCo2(mmHg)‐RoomairEtCo2(mmHg) FLAIR‐MRI‐images were assigned Fazekas‐scores by a neuroradiologist. AD‐Biomarkers Aβ40, Aβ42, tau, and p‐tau181(pg/ml), were measured in cerebrospinal fluid (CSF) and vascular‐biomarkers HbA1c (mg/dL), homocysteine (umol/l), HDL(mg/dL), and LDL (mg/dL) in blood. Vascular‐Risk‐Score (VRS) is a composite score based on the presence of hypertension, hypercholesterolemia, diabetes, smoking or obesity (body mass index&gt;30 kg/m2).ResultsTable‐1 summarizes participant‐demographics. CBF‐CVR (%/mmHg) differentiated diagnostic‐categories, and was lower in impaired vs. HC (p=0.027, Figure‐2a). Higher CBF‐CVR predicted better cognitive‐performance [MoCA(p=0.000089) (Figure‐2b), composite‐cognition (p=0.007) and language (p=0.000064)], physical function [faster gait(p=0.001), chair‐stands(p=0.021)], and disease‐severity [global‐CDR (p=0.003), CDR‐sum‐of‐boxes (p=0.001)(Table‐2). These relationships remained after adjusting for AD‐biomarkers. CBF‐CVR remained associated with cognition and physical‐function except chair‐stands, after adjusting for vascular‐markers: WMH‐Fazekas‐score, VRS, and whole‐brain‐CBF(Table‐2). CBF‐CVR was associated with HbA1c(p=0.007) and history of Diabetes (p=0.043), but not other blood biomarkers or VRS.ConclusionWe show that a 3‐minute CBF‐based CVR MRI can differentiate diagnostic‐categories, and predict cognitive and physical function, independent of AD pathology.

Haemodynamic changes in cirrhosis following terlipressin and induction of sepsis\u2014a preclinical study using caval subtraction phase-contrast and cardiac MRI

ObjectivesEffects of liver disease on portal venous (PV), hepatic arterial (HA), total liver blood flow (TLBF), and cardiac function are poorly understood. Terlipressin modulates PV flow but effects on HA, TLBF, and sepsis/acute-on-chronic liver failure (ACLF)-induced haemodynamic changes are poorly characterised. In this study, we investigated the effects of terlipressin and sepsis/ACLF on hepatic haemodynamics and cardiac function in a rodent cirrhosis model using caval subtraction phase-contrast (PC) MRI and cardiac cine MRI.MethodsSprague-Dawley rats (n = 18 bile duct–ligated (BDL), n = 16 sham surgery controls) underwent caval subtraction PCMRI to estimate TLBF and HA flow and short-axis cardiac cine MRI for systolic function at baseline, following terlipressin and lipopolysaccharide (LPS) infusion, to model ACLF.ResultsAll baseline hepatic haemodynamic/cardiac systolic function parameters (except heart rate and LV mass) were significantly different in BDL rats. Following terlipressin, baseline PV flow (sham 181.4 ± 12.1 ml/min/100 g; BDL 68.5 ± 10.1 ml/min/100 g) reduced (sham − 90.3 ± 11.1 ml/min/100 g, p < 0.0001; BDL − 31.0 ± 8.0 ml/min/100 g, p = 0.02), sham baseline HA flow (33.0 ± 11.3 ml/min/100 g) increased (+ 92.8 ± 21.3 ml/min/100 g, p = 0.0003), but BDL baseline HA flow (83.8 ml/min/100 g) decreased (− 34.4 ± 7.5 ml/min/100 g, p = 0.11). Sham baseline TLBF (214.3 ± 16.7 ml/min/100 g) was maintained (+ 2.5 ± 14.0 ml/min/100 g, p > 0.99) but BDL baseline TLBF (152.3 ± 18.7 ml/min/100 g) declined (− 65.5 ± 8.5 ml/min/100 g, p = 0.0004). Following LPS, there were significant differences between cohort and change in HA fraction (p = 0.03) and TLBF (p = 0.01) with BDL baseline HA fraction (46.2 ± 4.6%) reducing (− 20.9 ± 7.5%, p = 0.03) but sham baseline HA fraction (38.2 ± 2.0%) remaining unchanged (+ 2.9 ± 6.1%, p > 0.99). Animal cohort and change in systolic function interactions were significant only for heart rate (p = 0.01) and end-diastolic volume (p = 0.03).ConclusionsCaval subtraction PCMRI and cardiac MRI in a rodent model of cirrhosis demonstrate significant baseline hepatic haemodynamic/cardiac differences, failure of the HA buffer response post-terlipressin and an altered HA fraction response in sepsis, informing potential translation to ACLF patients.Key PointsCaval subtraction phase-contrast and cardiac MRI demonstrate:• Significant differences between cirrhotic/non-cirrhotic rodent hepatic blood flow and cardiac systolic function at baseline.• Failure of the hepatic arterial buffer response in cirrhotic rodents in response to terlipressin.• Reductions in hepatic arterial flow fraction in the setting of acute-on-chronic liver failure.

Highly accelerated, real-time phase-contrast MRI using radial k-space sampling and GROG-GRASP reconstruction: a feasibility study in pediatric patients with congenital heart disease.

Retrospective electrocardiogram-gated, 2D phase-contrast (PC) flow MRI is routinely used in clinical evaluation of valvular/vascular disease in pediatric patients with congenital heart disease (CHD). In patients not requiring general anesthesia, clinical standard PC is conducted with free breathing for several minutes per slice with averaging. In younger patients under general anesthesia, clinical standard PC is conducted with breath-holding. One approach to overcome this limitation is using either navigator gating or self-navigation of respiratory motion, at the expense of lengthening scan times. An alternative approach is using highly accelerated, free-breathing, real-time PC (rt-PC) MRI, which to date has not been evaluated in CHD patients. The purpose of this study was to develop a 38.4-fold accelerated 2D rt-PC pulse sequence using radial k-space sampling and compressed sensing with 1.5 × 1.5 × 6.0 mm3 nominal spatial resolution and 40 ms nominal temporal resolution, and evaluate whether it is capable of accurately measuring flow in 17 pediatric patients (aortic valve, pulmonary valve, right and left pulmonary arteries) compared with clinical standard 2D PC (either breath-hold or free breathing). For clinical translation, we implemented an integrated reconstruction pipeline capable of producing DICOMs of the order of 2 min per time series (46 frames). In terms of association, forward volume, backward volume, regurgitant fraction, and peak velocity at peak systole measured with standard PC and rt-PC were strongly correlated (R2 > 0.76; P < 0.001). Compared with clinical standard PC, in terms of agreement, forward volume (mean difference = 1.4% (3.0% of mean)) and regurgitant fraction (mean difference = -2.5%) were in good agreement, whereas backward volume (mean difference = -1.1 mL (28.2% of mean)) and peak-velocity at peak systole (mean difference = -21.3 cm/s (17.2% of mean)) were underestimated by rt-PC. This study demonstrates that the proposed rt-PC with the said spatial resolution and temporal resolution produces relatively accurate forward volumes and regurgitant fractions but underestimates backward volumes and peak velocities at peak systole in pediatric patients with CHD.

Altered 4-D magnetic resonance imaging flow characteristics in complex congenital aortic arch repair

Interrupted aortic arch (IAA) is a rare but severe congenital abnormality often associated with bicuspid aortic valve (BAV). Complex re-interventions are often needed despite surgical advances, but the impact of aortic hemodynamics in repaired patients is unknown. Investigate effect of IAA repairs on aortic hemodynamics, wall shear stress and flow derangements via 4-D flow MRI. We retrospectively analyzed age- and gender-matched cohorts (IAA [n=6], BAV alone [n=6], controls [n=6]) undergoing cardiac MRI including 4-D flow. Aortic dimensions were measured from standard MR angiography. We quantified peak systolic velocities, regurgitant fractions and wall shear stress in the ascending aorta (AAo), transverse arch and descending aorta (DAo) from 4-D flow, and we graded helix/vortex flow patterns from 3-D blood flow visualization. Children and young adults with IAA had a wide range of arch dimensions, peak systolic velocities, regurgitant fractions and flow grades. Peak transverse arch systolic velocities were higher in patients with IAA versus controls (P=0.02). Flow derangements in the AAo were found in patients with IAA (median grade=2, 5/6 patients, P=0.04) and BAV (median grade=3, 5/6 patients, P=0.03) versus controls. Flow derangements in the DAo were only seen in patients with IAA (median grade=1, 5/6 patients, P=0.04), and 5/6 people with IAA had helical flow in head and neck vessels. Wall shear stress was increased in people with IAA along the superior transverse arch and proximal DAo versus controls (P=0.02). Complex congenital aortic arch repairs can change aortic hemodynamics. Associated cardiac defects can further alter findings. Studies are warranted to investigate clinical implications in larger cohorts.

Non-contrast-enhanced magnetic resonance imaging for visualization and quantification of endovascular aortic prosthesis, their endoleaks and aneurysm sacs at 1.5 T

PurposeAfter an endovascular aortic aneurysm repair (EVAR), a follow-up at 1, 6 and every 12 months is recommended for remainder of the patient's life. The diagnostic standard methods for diagnosing endoleaks and visualization of aneurysms in EVAR-patients are: invasive digital subtraction angiography (DSA), contrast enhanced (CE) computed tomographic angiography (CE-CTA), and magnetic resonance angiography (CE-MRA). These techniques, however, require the use of iodine- or gadolinium-based contrast agents with rare, but possibly life threatening side effects such as renal impairment, thyrotoxicosis and allergic reactions, nephrogenic systemic fibrosis, and cerebral gadolinium deposition. The aim of this prospective study was to compare a non-contrast-enhanced MRI protocol (consist of four MRI methods) with DSA and CE-CTA for visualization and quantification of endovascular aortic prosthesis, their endoleaks and aneurysms. Material and methodsEight patients (mean age 76.8 ± 4.9 years, 63% male), whose thoracic, abdominal, or iliac aneurysms were treated with different endovascular prosthesis and suffered from type I–V endoleaks, were examined on a 1.5 Tesla MR system. Quiescent-interval slice selective MR angiography (QISS-MRA), 4-dimensional (4D)-flow MRI, T1- and T2-mapping, as well as DSA and CE-CTA were used for the visualization and quantification of endoprosthesis, endoleaks, and aneurysms in these patients. ResultsQISS-MRA provided good visualization of endoleaks and comparable quantification of aneurysm size with respect to CE-CTA and DSA. The 4D-flow MRI provided additional information about the wall shear stress, which could not be determined using DSA. In contrast to CE-CTA, T1- and T2-mapping provided detailed information about heterogeneous areas within an aneurysm sac. ConclusionsCompared to DSA and CE-CTA, the proposed MRI methods provide improved anatomical and functional information for various types of endoprostheses and endoleaks. In addition, hemodynamic parameters of the aorta and information on the content of aneurysm sac are provided as well. Within the frame of personalized medicine, the personalized diagnosis enabled by this non-CE MRI protocol is the foundation for a personalized and successful treatment.

Evaluation of Flow Pattern in the Ascending Aorta in Patients with Repaired Tetralogy of Fallot Using Four-Dimensional Flow Magnetic Resonance Imaging.

ObjectiveTo evaluate flow pattern characteristics in the ascending aorta (AA) with four-dimensional (4D)-flow MRI and to determine predictors of aortic dilatation late after tetralogy of Fallot (TOF) repair.Materials and MethodsThis study included 44 patients with repaired TOF (25 males and 19 females; mean age, 28.9 ± 8.4 years) and 11 volunteers (10 males and 1 female, mean age, 33.7 ± 8.8 years) who had undergone 4D-flow MRI. The aortic diameters, velocity, wall shear stress (WSS), flow jet angle (FJA), and flow displacement (FD) at the level of the sinotubular junction (STJ) and mid-AA were compared between the repaired TOF and volunteer groups. The hemodynamic and clinical parameters were also compared between the aortic dilatation and non-dilatation subgroups in the repaired TOF group.ResultsThe diameters of the sinus of Valsalva, STJ, and AA were significantly higher in the repaired TOF group than in the volunteer group (p = 0.002, p < 0.001, and p = 0.013, respectively). The FJAs at the STJ and AA were significantly greater in the repaired TOF group (p < 0.001 and p = 0.003, respectively), while velocities and WSS parameters were significantly lower. FD showed no statistically significant difference (p = 0.817). In subgroup analysis, age at TOF repair was significantly higher (p = 0.039) and FJA at the level of the AA significantly greater (p = 0.003) and mean WSS were significantly lower (p = 0.039) in the aortic dilatation group. FD were higher in the aortic dilatation group without statistical significance (p = 0.217).ConclusionPatients with repaired TOF have an increased FJA, dilated AA, and secondarily decreased WSS. In addition to known risk factors, flow eccentricity may affect aortic dilatation in patients with repaired TOF.

Volumetric quantification of absolute local normalized helicity in patients with bicuspid aortic valve and aortic dilatation.

Absolute local normalized helicity (LNH) can differentiate flow alterations in the aorta between healthy controls and bicuspid aortic valve (BAV) patients. A total of 65 controls and 50 subjects with BAV underwent in vivo four-dimensional (4D) flow MRI. Data analysis included the three-dimensional (3D) segmentation of the thoracic aorta (ascending aorta, aortic arch, and descending aorta) and calculation of absolute LNH. The mean velocity in the entire aorta was used to identify peak systole, systolic deceleration, and middiastole. A sensitivity analysis was performed to identify the optimal absolute LNH threshold, comparing control and BAV groups. A reproducibility test was performed for 3D segmentation and absolute LNH. Absolute LNH above 0.6 was significantly higher (P < 0.001) in BAV in comparison to controls for all aortic segments and cardiac time frames. Absolute LNH in the ascending aorta correlated with maximal aortic diameter (R = 0.83, P < 0.001, at peak systole; r = 0.84, P < 0.001, at systolic deceleration; R = 0.88, P < 0.001, at middiastole) and significantly increased (P < 0.001) with aortic stenosis severity. Intra- and interobserver errors were 5 ± 2% and 12 ± 6% for 3D segmentation and 7 ± 6% and 12 ± 7% for absolute LNH. Absolute LNH can differentiate between controls and subjects with aortic dilatation, and was associated with maximal aortic diameter and aortic stenosis severity. Magn Reson Med 78:689-701, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Four-dimensional MRI flow examinations in cerebral and extracerebral vessels - ready for clinical routine?

To evaluate the feasibility of 4-dimensional (4D) flow MRI for the clinical assessment of cerebral and extracerebral vascular hemodynamics in patients with neurovascular disease. 4D flow MRI has been applied in multiple studies to qualitatively and quantitatively study intracranial aneurysm blood flow for potential risk stratification and to assess treatment efficacy of various neurovascular lesions, including intraaneurysmal and parent artery blood flow after flow diverter stent placement and staged embolizations of arteriovenous malformations and vein of Galen aneurysmal malformations. Recently, the technique has been utilized to characterize age-related changes of normal cerebral hemodynamics in healthy individuals over a broad age range. 4D flow MRI is a useful tool for the noninvasive, volumetric and quantitative hemodynamic assessment of neurovascular disease without the need for gadolinium contrast agents. Further improvements are warranted to overcome technical limitations before broader clinical implementation. Current developments, such as advanced acceleration techniques (parallel imaging and compressed sensing) for faster data acquisition, dual or multiple velocity encoding strategies for more accurate arterial and venous flow quantification, ultrahigh-field strengths to achieve higher spatial resolution and streamlined postprocessing workflow for more efficient and standardized flow analysis, are promising advancements in 4D flow MRI.

Evaluation of blood flow distribution asymmetry and vascular geometry in patients with Fontan circulation using 4-D flow MRI.

Asymmetrical caval to pulmonary blood flow is suspected to cause complications in patients with Fontan circulation. The aim of this study was to test the feasibility of 4-D flow MRI for characterizing the relationship between 3-D blood flow distribution and vascular geometry. We hypothesized that both flow distribution and geometry can be calculated with low interobserver variability and will detect a direct relationship between flow distribution and Fontan geometry. Four-dimensional flow MRI was acquired in 10 Fontan patients (age: 16 ± 4years [mean ± standard deviation], range: 9-21years). The Fontan connection was isolated by 3-D segmentation to evaluate flow distribution from the inferior vena cava (IVC) and superior vena cava (SVC) to the left and right pulmonary arteries (LPA, RPA) and to characterize geometry (cross-sectional area, caval offset, vessel angle). Flow distribution results indicated SVC flow tended toward the RPA while IVC flow was more evenly distributed (SVC to RPA: 78% ± 28 [9-100], IVC to LPA: 54% ± 28 [4-98]). There was a significant relationship between pulmonary artery cross-sectional area and flow distribution (IVC to RPA: R(2)=0.50, P=0.02; SVC to LPA: R(2)=0.81, P=0.0004). Good agreement was found between observers and for flow distribution when compared to net flow values. Four-dimensional flow MRI was able to detect relationships between flow distribution and vessel geometry. Future studies are warranted to investigate the potential of patient specific hemodynamic analysis to improve diagnostic capability.

Does altered aortic flow in marfan syndrome relate to aortic root dilatation?

PurposeTo examine possible hemodynamic alterations in adolescent to adult Marfan syndrome (MFS) patients with aortic root dilatation.Materials and MethodsFour‐dimensional flow MRI was performed in 20 MFS patients and 12 age‐matched normal subjects with a 3T system. The cross‐sectional areas of 10 planes along the aorta were segmented for calculating the axial and circumferential wall shear stress (WSSaxial, WSScirc), oscillatory shear index (OSIaxial, OSIcirc), and the nonroundness (NR), presenting the asymmetry of segmental WSS. Pearson's correlation analysis was performed to present the correlations between the quantified indices and the body surface area (BSA), aortic root diameter (ARD), and Z score of the ARD. P < 0.05 indicated statistical significance.ResultsPatients exhibited lower WSSaxial in the aortic root and the WSScirc in the arch (P < 0.05–0.001). MFS patients exhibited higher OSIaxial and OSIcirc in the sinotubular junction and arch, but lower OSIcirc in the descending aorta (all P < 0.05). The NR values were lower in patients (P < 0.05). The WSSaxial or WSScirc exhibited moderate to strong correlations with BSA, ARD, or Z score (R2 = 0.50–0.72) in MFS patients.ConclusionThe significant differences in the quantified indices, which were associated with BSA, ARD, or Z score, in MFS were opposite to previous reports for younger MFS patients, indicating that altered flows in MFS patients may depend on the disease progress. The possible time dependency of hemodynamic alterations in MFS patients strongly suggests that longitudinal follow‐up of 4D Flow is needed to comprehend disease progress. J. Magn. Reson. Imaging 2016;44:500–508.

4D Flow and 2D PC MRI: impact of volumetric coverage and three-directional velocity encoding on quantification of aortic hemodynamics

4D Flow and 2D PC MRI: impact of volumetric coverage and three-directional velocity encoding on quantification of aortic hemodynamics

SP-0020: Full integration of MRI in the work flow of external-beam radiotherapy

SP-0020: Full integration of MRI in the work flow of external-beam radiotherapy

Beta-blocker therapy does not reduce ascending aorta wall shear stress in patients with bicuspid aortic valve

Methods Right-left coronary leaflet fusion BAV patients on b-blockers (BB+) (n = 30, M:F = 23:7, age: 46 ± 14 years) and not on b-blockers (BB-) (n=30, M:F = 23:7, age: 46 ± 13 years) and healthy controls (n=15, age:43±11 years) underwent time-resolved, 3D phase contrast (4D flow) MRI. Patient groups were matched by systolic blood pressure (SBP), degree of aortic stenosis (AS), and AAo diameter (3.9 ± 0.7 vs. 3.9 ± 0.6 cm, p = 0.70). A 3D segmentation of the thoracic aorta was performed (MIMICS, Materlise, Belgium). Systolic 3D WSS was calculated in the thoracic aorta from 4D flow velocity acquisition and a sagittal maximum intensity projection (MIP) of WSS was generated.