Phase-contrast Cardiovascular Magnetic Resonance Research Articles

How to estimate aortic characteristic impedance from magnetic resonance and applanation tonometry data?

Compare seven previous methods for the estimation of aortic characteristic impedance, which contributes to left ventricle pulsatile load, from phase-contrast cardiovascular magnetic resonance (CMR) and applanation tonometry data. We studied 77 healthy (43 ± 16 years) individuals and 16 hypertensive (61 ± 9 years) patients, who consecutively underwent ascending aorta CMR and carotid tonometry, resulting in flow and pressure waveforms, respectively. Characteristic impedance was semi-automatically estimated in time domain from these latter waveforms, using seven methods. The methods were based on the following: methods 1-4, magnitudes at specific times; method 5, early-systolic up-slope; method 6, time-derivatives peak; and method 7, pressure-flow loop early-systolic slope. Aortic characteristic impedance was significantly increased in hypertensive patients when compared to elderly controls (n = 32) with a similar mean age of (59 ± 8 years) when using methods based on 95% of peak flow, up-slopes, and derivatives peaks (P < 0.05). When considering healthy individuals, impedance indices were significantly correlated to central pulse pressure for all methods (P < 0.005). Finally, characteristic impedance was correlated to the frequency-domain reference values (r > 0.65, P < 0.0001), with a slight superiority for the same three methods as above (r > 0.82, P < 0.0001). This is the first study demonstrating phase-contrast CMR and tonometry usefulness in aortic characteristic impedance temporal estimation. Methods based on 95% of peak flow, as well as those based on derivative peaks and up-slopes, which are fast and independent of curve preprocessing, were slightly superior. They can be easily integrated in a clinical workflow and may help to understand the complementarity of this pulsatile index with other CMR aortic geometry and stiffness measures in the setting of left ventricle-aortic coupling.

Fetal blood flow measured using phase contrast MRI-comparison of image quality and flow volume at 1.5T with 3.0T

Background Ultrasound is commonly used for the antenatal assessment of a fetus and it can provide functional and haemodynamic data in addition to anatomical details. The accuracy of the former is dependant on angle of insonation, maternal habitus and fetal position. Phase contrast cardiovascular magnetic resonance (PC CMR) has emerged as a clinical tool for blood flow quantification but its use in the foetus has been hampered by the need for gating with the fetal heart beat. Previously described metric optimized gating (MOG) technique has been successfully used to measure fetal blood flow in late gestation foetuses on a 1.5T MRI magnet. However, there is increasing interest in performing foetal cardiac imaging using 3.0T MRI. We describe our pilot data of fetal blood flow measured in 3.0T MRI using MOG technique. Methods Fetal blood flows were quantified in 5 subjects at late gestational age (35-38 weeks) of which were two normal and three pregnancies with ventricular size discrepancy. The data were obtained on 1.5T and 3.0T (Siemens Avanto and TRIO, respectively) within the same day using a previously described protocol. After MOG reconstruction of PC MR data, blood flow was quantified by using Q flow (Medis, NL) and adjusted for fetal mass. Reproducibility of flow measurements at the two field strengths was assessed by Pearson correlation coefficient (R 2 ), linear regression and Bland Altman analysis.

Biomarkers of hemodynamic stress and aortic stiffness post-STEMI: a cross-sectional analysis

Methods Fifty-four patients four months after acute STEMI were enrolled in this cross-sectional, single-center study. Nterminal pro B-type natriuretic peptide (NT-proBNP), mid-regional pro-A-type natriuretic peptide (MR-proANP) and mid-regional pro-adrenomedullin (MR-proADM) levels were measured by established assays. Aortic stiffness was assessed by the measurement of pulse wave velocity using velocity-encoding, phase-contrast cardiovascular magnetic resonance imaging.

Foetal blood flow measured using phase contrast cardiovascular magnetic resonance--preliminary data comparing 1.5 T with 3.0 T.

BackgroundPhase contrast cardiovascular magnetic resonance (PC CMR) has emerged as a clinical tool for blood flow quantification but its use in the foetus has been hampered by the need for gating with the foetal heart beat. The previously described metric optimized gating (MOG) technique has been successfully used to measure foetal blood flow in late gestation foetuses on a 1.5 T CMR magnet. However, there is increasing interest in performing foetal cardiac imaging using 3.0 T CMR. We describe our pilot investigation of foetal blood flow measured using 3.0 T CMR.MethodsFoetal blood flows were quantified in 5 subjects at late gestational age (35–38 weeks). Three were normal pregnancies and two were pregnancies with ventricular size discrepancy. Data were obtained at 1.5 T and 3.0 T using a previously described PC CMR protocol. After reconstruction using MOG, blood flow was quantified independently by two observers. Intra- and inter-observer reproducibility of flow measurements at the two field strengths was assessed by Pearson correlation coefficient (R2), linear regression and Bland Altman analysis.ResultsPC CMR flow measurements were obtained in 36 of 40 target vessels. Strong intra-observer agreement was obtained between measurements at each field strength (R2 = 0.78, slope = 0.83 ± 0.11), with a mean bias of −1 ml/min/kg and 95% confidence limits of ±71 ml/min/kg. Inter-observer agreement was similarly high for measurements at both 1.5 T (R2 = 0.86, slope = 0.95 ± 0.13, bias = 6 ± 52 ml/min/kg) and 3.0 T (R2 = 0.88, slope = 0.94 ± 0.13, bias = 4 ± 47 ml/min/kg). Across all PC CMR measurements, SNR per pixel was expectedly higher at 3.0 T relative to 1.5 T (165 ± 50%). The relative differences in flow measurements between observers were low (range: 4–16%) except for pulmonary blood flow which showed much higher variability at 1.5 T (34%) versus that at 3.0 T (11%). This was attributed to the poorly visualized, small pulmonary vessels at 1.5 T, which made delineation inconsistent between observers.ConclusionsThis is the first pilot study to measure foetal blood flow using PC CMR at 3.0 T. The flow data obtained were in good correlation with those measured at 1.5 T, both within and between observers. With increased SNR at 3.0 T, smaller pulmonary vessels were better visualized which improved inter-observer agreement of associated flows.Electronic supplementary materialThe online version of this article (doi:10.1186/s12968-015-0132-2) contains supplementary material, which is available to authorized users.

Baseline correction does not improve flow quantification in phase-contrast velocity measurement for routine clinical practice

IntroductionVelocity offset errors may influence flow measurement in phase-contrast cardiovascular magnetic resonance (CMR). By using a stationary gel phantom, offset errors probably may be corrected. We tested its impact on flow measurement and, in particular, on shunt calculation in patients proven not to have any shunt. MethodsFlow measurements were carried out in 24 patients with congenital heart disease. Baseline correction was performed by using a stationary gel phantom. ResultsSignificantly more patients without shunts incorrectly showed a calculated shunt after baseline correction. ConclusionsBaseline correction did not improve flow measurement and was clinically not relevant for routine CMR.

Analysis of temperature dependence of background phase errors in phase-contrast cardiovascular magnetic resonance.

BackgroundThe accuracy of phase-contrast cardiovascular magnetic resonance (PC-CMR) can be compromised by background phase errors. It is the objective of the present work to provide an analysis of the temperature dependence of background phase errors in PC-CMR by means of gradient mount temperature sensing and magnetic field monitoring.MethodsBackground phase errors were measured for various temperatures of the gradient mount using magnetic field monitoring and validated in a static phantom. The effect of thermal changes during k-space acquisition was simulated and confirmed with measurements in a stationary phantom.ResultsThe temperature of the gradient mount was found to increase by 20–30 K during PC-CMR measurements of 6–12 min duration. Associated changes in background phase errors of up to 11% or 0.35 radian were measured at 10 cm from the magnet’s iso-center as a result of first order offsets. Zeroth order phase errors exhibited little thermal dependence.ConclusionsIt is concluded that changes in gradient mount temperature significantly modify background phase errors during PC-CMR with high gradient duty cycle. Since temperature increases significantly during the first minutes of scanning the results presented are also of relevance for single-slice or multi-slice PC-CMR scans. The findings prompt for further studies to investigate advanced correction methods taking into account gradient temperature and/or the use of concurrent field-monitoring to map gradient-induced fields throughout the scan.

Real-Time Magnetic Resonance–Guided Aortic Valve Replacement Using Engager Valve

New-generation stented bioprostheses coupled with better imaging modalities are expanding the clinical utility of transcatheter aortic valve replacement (TAVR). This study aimed at evaluating the feasibility of real-time cardiovascular magnetic resonance (rtCMR) -guided TAVR using the Medtronic Engager aortic valve system in a preclinical model. The Engager delivery device was slightly modified to make it CMR-compatible. Ten Yucatan swine underwent rtCMR-guided transapical TAVR. Postplacement phase-contrast and first-pass perfusion CMR sequences were used to evaluate for aortic regurgitation and myocardial perfusion, respectively. Real-time CMR provided excellent visualization of cardiac anatomy during TAVR. Nine of 10 animals had proper valve placement in the aortic annulus as determined by CMR and confirmed by necropsy inspection. Postplacement phase-contrast scans confirmed no intravalvular or paravalvular leaks. Perfusion scans demonstrated sufficient coronary flow. Roentgenographs confirmed proper placement of the prostheses. The Engager valve can be implanted transapically under rtCMR guidance with a modified, CMR-compatible delivery device in a preclinical model. Cardiovascular magnetic resonance allowed for accurate preplacement evaluation, real-time guidance, and postplacement functional assessment.

Geometry is a major determinant of flow reversal in proximal aorta

The aim of this study is to quantify aortic backward flow (BF) using phase-contrast cardiovascular magnetic resonance (PC-CMR) and to study its associations with age, indexes of arterial stiffness, and geometry. Although PC-CMR blood flow studies showed a simultaneous presence of BF and forward flow (FF) in the ascending aorta (AA), the relationship between aortic flows and aging as well as arterial stiffness and geometry in healthy volunteers has never been reported. We studied 96 healthy subjects [47 women, 39 ± 15 yr old (19-79 yr)]. Aortic stiffness [arch pulse wave velocity (PWVAO), AA distensibility], geometry (AA diameter and arch length), and parameters related to AA BF and FF (volumes, peaks, and onset times) were estimated from CMR. Applanation tonometry carotid-femoral pulse-wave velocity (PWVCF), carotid augmentation index, and time to return of the reflected pressure wave were assessed. Whereas FF parameters remained unchanged, BF onset time shortened significantly (R(2) = 0.18, P < 0.0001) and BF volume and BF-to-FF peaks ratio increased significantly (R(2) = 0.38 and R(2) = 0.44, respectively, P < 0.0001) with aging. These two latter BF indexes were also related to stiffness indexes (PWVCF, R(2) > 0.30; PWVAO, R(2) > 0.24; and distensibility, R(2) > 0.20, P < 0.001), augmentation index (R(2) > 0.20, P < 0.001), and aortic geometry (AA diameter, R(2) > 0.58; and arch length, R(2) > 0.31, P < 0.001). In multivariate analysis, aortic diameter was the strongest independent correlate of BF beyond age effect. In conclusion, AA BF estimated using PC-CMR increased significantly in terms of magnitude and volume and appeared earlier with aging and was mostly determined by aortic geometry. Thus BF indexes could be relevant markers of subclinical arterial wall alterations.

Association of aortic stiffness with biomarkers of myocardial wall stress after myocardial infarction

BackgroundAortic pulse wave velocity (PWV) was linked to LV-geometry and -function in patients with kidney disease and non-ischemic cardiomyopathy. The role of aortic compliance after acute STEMI is so far unknown. In the present study, we prospectively investigated the relationship of increased aortic stiffness with biomarkers of myocardial wall stress 4months after STEMI. Methods48 STEMI patients who were reperfused by primary coronary angioplasty underwent cardiovascular magnetic resonance (CMR) at baseline and at 4-month follow-up. The CMR protocol comprised cine-CMR as well as gadolinium contrast-enhanced CMR. Aortic PWV was determined by velocity-encoded, phase-contrast CMR. Blood samples were routinely drawn at baseline and follow-up to determine N-terminal pro-B-type natriuretic peptide (NT-proBNP). In a subgroup of patients, mid-regional pro-adrenomedullin (MR-proADM) and mid-regional pro-A-type natriuretic peptide (MR-proANP) levels were determined. ResultsPatients with a PWV above median (>7.0m/s) had significantly higher NT-proBNP, MR-proADM and MR-proANP concentrations at 4-month follow-up than patients with a PWV below median (all p<0.02). PWV showed moderate to good correlation with NT-proBNP, MR-proAMD and MR-proANP levels 4months after STEMI (all p<0.05). Multivariate analysis revealed PWV, beside myocardial infarct size, as an independent predictor of 4-month NT-proBNP levels after correction for age, creatinine and LV ejection fraction (model r: 0.781, p<0.001). ConclusionAortic stiffness is directly associated with biomarkers of myocardial wall stress 4months after reperfused STEMI, suggesting a role for aortic stiffness in chronic LV-remodelling.

Bioprosthetic mitral valve effective orifice area by phase-contrast CMR. An in vitro comparison with Doppler echocardiography

Background Introduction: Current guidelines for the functional evaluation of bioprosthetic heart valves recommend the effective orifice area (EOA) as the product of the transvalvular stroke volume divided by Doppler derived diastolic time velocity integral (TVI). Phase contrast CMR may offer an alternative imaging modality to assess bioprosthetic valve EOA when Doppler methods are technically limited or unreliable. Methods Our circulatory loop includes a mock ventricle and a heart valve imaging chamber that has been fabricated using MRI-compatible components. In this study 3 different sized stented porcine mitral valve bioprostheses were evaluated (27 mm, 29 mm, 31 mm) replicating three different hemodynamic conditions with forward stroke volume of 70 ml, 90 ml and 110 ml respectively at a beat rate of 70 bpm. Imaging was performed with a

Accelerated 4D flow imaging using randomly undersampled echo planer imaging with compressed-sensing reconstruction

Background 4D flow imaging using phase contrast CMR (PC CMR) allows visualization and quantification of blood flow. One of the major limitations of 4D flow imaging is its long scan time (in the order of 10-20 min). In this study, we sought to investigate an accelerate 4D flow imaging sequence that combines an efficient data sampling strategy using echo planar imaging (EPI) with randomly undersampled 3D k-space sampling pattern. The randomly undersampled k-space data are then reconstructed using compressed sensing (CS). Methods Figure 1 shows the k-space acquisition strategy. Similar to regular EPI acquisition, the k-space data are divided into multiple segments. For each segment, the profiles are undersampled with the CS rate such that all EPI segments have the same undersampling pattern. The proposed EPI random sampling strategy was implemented. Seven subjects were recruited (26 ± 12 years; 3 males) for 4D flow CMR on a 1.5T Philips Achieva magnet. Images were acquired axially using a GRE sequence (FOV =3 40 ×2 80 ×6 0 mm 3 ,r esolution =2× 2×3m m 3 ,T R/TE/a = 7.4/3.8 ms/20°, EPI factor = 3, Turbo Factor =2 , CS rate =3 ) in av olume covering the ascending and descending aorta, and the aortic bifurcation. Only foot-head flow encoding was used to provide an adequate temporal resolution of 30 ms for the measurements. A single beam navigator placed on the right hemi-diaphragm was used to gate the acquisition with the respiratory cycle. The nominal scan time for this scan was 3:30 minutes at 70 bpm assuming 100% gating efficiency (vs. 8:40 minutes if standard parallel imaging with rate 4 was used). For each subject, the 4D-PC scan was followed by a standard breath-hold 2D-PC scan with the same flow encoding direction (FOV = 340 × 280 mm2, resolution = 2 × 2 mm 2 , slice thickness = 5 mm 3 , SENSE rate = 2.5). The acquired 2D slice is selected from the previously obtained 4D scan and approximately at the aortic bifurcation. Data are then transferred to a separate station where the CS reconstruction was performed using a total variation minimization algorithm. Next, flow quantifications were performed on both the ascending and the descending aorta for all acquisitions and then compared between the 2D scans and the corresponding slices in the 4D scans.

RV work efficiency is greatly reduced in patients with pulmonary arterial hypertension as evidenced by 4D flow cardiac MRI

Background The dynamic assessment of intracardiac flow remained challenging until the recent development of timeresolved 3D phase-contrast CMR (PC-CMR), which allows for assessment of multi-dimensional whole heart and great vessel flow. Previous studies have used this technique in the ventricles to quantify flow type of the ventricle and the kinetic energy of each flow component. In the great vessels, parameters such as total flow, peak systolic velocity, and wall shear stress have excellent scan-rescan, inter-observer, and intra-observer reproducibility. In disease conditions, pathological vortices have been reported both in the ventricles and great vessels. We propose to use time-resolved 3D PC-CMR to study right ventricular (RV) work in patients with pulmonary arterial hypertension (PAH) as compared to normal subjects.

DEVELOPMENT OF A MULTI-MODALITY IMAGING MODEL OF DYNAMIC MITRAL VALVE DYSFUNCTION

A robust, controlled in vitro model of mitral valve regurgitation (MR) would facilitate the exploration of MR repair techniques and provide a reference test environment for the validation of new imaging applications – including 3D Doppler and phase contrast CMR. Design software, 3D printing

Novel insight into the detailed myocardial motion and deformation of the rodent heart using high-resolution phase contrast cardiovascular magnetic resonance.

BackgroundPhase contrast velocimetry cardiovascular magnetic resonance (PC-CMR) is a powerful and versatile tool allowing assessment of in vivo motion of the myocardium. However, PC-CMR is sensitive to motion related artifacts causing errors that are geometrically systematic, rendering regional analysis of myocardial function challenging. The objective of this study was to establish an optimized PC-CMR method able to provide novel insight in the complex regional motion and strain of the rodent myocardium, and provide a proof-of-concept in normal and diseased rat hearts with higher temporal and spatial resolution than previously reported.MethodsA PC-CMR protocol optimized for assessing the motion and deformation of the myocardium in rats with high spatiotemporal resolution was established, and ten animals with different degree of cardiac dysfunction underwent examination and served as proof-of-concept. Global and regional myocardial velocities and circumferential strain were calculated, and the results were compared to five control animals. Furthermore, the global strain measurements were validated against speckle-tracking echocardiography, and inter- and intrastudy variability of the protocol were evaluated.ResultsThe presented method allows assessment of regional myocardial function in rats with high level of detail; temporal resolution was 3.2 ms, and analysis was done using 32 circumferential segments. In the dysfunctional hearts, global and regional function were distinctly altered, including reduced global peak values, increased regional heterogeneity and increased index of dyssynchrony. Strain derived from the PC-CMR data was in excellent agreement with echocardiography (r = 0.95, p < 0.001; limits-of-agreement −0.02 ± 3.92%strain), and intra- and interstudy variability were low for both velocity and strain (limits-of-agreement, radial motion: 0.01 ± 0.32 cm/s and −0.06 ± 0.75 cm/s; circumferential strain: -0.16 ± 0.89%strain and −0.71 ± 1.67%strain, for intra- and interstudy, respectively).ConclusionWe demonstrate, for the first time, that PC-CMR enables high-resolution evaluation of in vivo circumferential strain in addition to myocardial motion of the rat heart. In combination with the superior geometric robustness of CMR, this ultimately provides a tool for longitudinal studies of regional function in rodents with high level of detail.

Wall shear stress measured by phase contrast cardiovascular magnetic resonance in children and adolescents with pulmonary arterial hypertension.

BackgroundPulmonary arterial hypertension (PAH) is a devastating disease with significant morbidity and mortality. At the macroscopic level, disease progression is observed as a complex interplay between mean pulmonary artery pressure, pulmonary vascular resistance, pulmonary vascular stiffness, arterial size, and flow. Wall shear stress (WSS) is known to mediate or be dependent on a number of these factors. Given that WSS is known to promote architectural vessel remodeling, it is imperative that the changes of this factor be quantified in the presence of PAH.MethodsIn this study, we analyzed phase contrast imaging of the right pulmonary artery derived from cardiovascular magnetic resonance to quantify the local, temporal and circumferentially averaged WSS of a PAH population and a pediatric control population. In addition, information about flow and relative area change were derived.ResultsAlthough the normotensive and PAH shear waveform exhibited a WSS profile which is uniform in magnitude and direction along the vessel circumference at systole, time-averaged WSS (2.2 ± 1.6 vs. 6.6 ± 3.4 dynes/cm2, P = 0.018) and systolic WSS (8.2 ± 5.0 v. 20.0 ± 9.1 dynes/cm2, P = 0.018) was significantly depressed in the PAH population as compared to the controls. BSA-indexed PA diameter was significantly larger in the PAH population (1.5 ± 0.4 vs. 0.7 ± 0.1 cm/m2, P = 0.003).ConclusionsIn the presence of preserved flow rates through a large PAH pulmonary artery, WSS is significantly decreased. This may have implications for proximal pulmonary artery remodeling and cellular function in the progression of PAH.

Assessment of ductal blood flow in newborns with obstructive left heart lesions by cardiovascular magnetic resonance.

BackgroundNewborns with obstructive left heart lesions often depend on a patent ductus arteriosus to sustain the systemic circulation. Our aims were to validate the direct measurement of ductal flow, and to characterize the magnitude, determinants and hemodynamic effects of patent ductus arteriosus in newborns with obstructive left heart lesions by cardiovascular magnetic resonance (CMR).MethodsIn this retrospective study, the CMR and clinical information of newborns with obstructive left heart lesions were reviewed. The feasibility and validity of measuring ductal flow and the correlations between ductal flow and ventricular volumes, ascending aortic flow, post-ductal oxygen saturation and Qp:Qs were assessed.ResultsThe CMR examinations of 32 newborns were included. It was possible to measure the ductal flow in all of them, with moderate-to-good agreement between measured and calculated ductal flow volume. The flow was bidirectional in all patients, with a net right-to-left shunt in 72%. Net ductal flow correlated inversely with ascending aortic flow (Rho −0.63; p 0.0002), post-ductal oxygen saturation (Rho −0.58; p 0.0004), Qp:Qs (Rho −0.43; p 0.02), and with left ventricular end-diastolic volume index (Rho −0.38; p 0.04). There was no correlation with the diameter of the ductus. The contribution of ductus flow to the systemic circulation correlated with the left ventricular end-diastolic volume index (Rho −0.47; p 0.02).ConclusionsDirect measurement of ductal flow in newborns with obstructive left heart lesions is feasible. From these measurements, we were able to demonstrate that patients with smaller left ventricles and lower ascending aortic flow have a greater contribution of ductal flow to the systemic circulation. The size of the ductus arteriosus does not predict net ductal flow. Phase-contrast CMR can be an adjunct method for the assessment of the physiology for very ill neonate patients.

Intraventricular ejection pressure gradient derived from acceleration measurement by phase contrast CMR as a new marker of left ventricular contractility: feasibility study and preliminary results in dilated cardiomyopathy

Background Intra-ventricular pressure gradient along the direction of the outflow tract is generated by the impulse response of the myocardial contraction. This spatial pressure gradient, derived from the maximal acceleration estimates within the left ventricular (LV) ejection flow, has been validated in vitro by using MRI and was found strongly related to the inotropic state of the LV as demonstrated in animal and human echocardiographic studies. This acceleration may be less dependant on load conditions than others LV systolic function parameters, especially LV ejection fraction (LVEF). Aim: (1) to evaluate the feasibility of LV ejection flow acceleration (Acc) estimates by spatial and temporal derivative of velocities recorded by CMR using phase contrast sequence, (2) to compare the acceleration values to LVEF in patients with Dilated Cardiomyopathy (LVEF<50%) and in control subjects. Methods

Improved efficiency for respiratory motion compensation in three-dimensional flow measurements

Background Phase contrast (PC) CMR is clinically used for in-vivo assessment of blood flow in cardiovascular disease [1]. Typically, a through-plane 2D acquisition is performed for evaluating the blood flow. Recently, 3D time-resolved PC CMR has been used for quantification and visualization of the blood flow in all three directions of a volume [2]. However, such acquisitions require long scan times, which are further prolonged by the need for respiratory motion compensation, typically using respiratory navigators. In this study, we hypothesized that respiratory gating the center of k-space only will yield similar measurements to a fully respiratory-gated acquisition, since the phase information is mainly coming from the central k-space, and evaluated these two gating approaches.

Cardiovascular 4D velocity mapping accelerated with k-t BLAST at 3.0 Tesla: 8-channel vs. 32-channel coil arrays

Background 4D phase contrast CMR can be used to visualise and quantify cardiovascular flow and has become more widely available. However, the scan times tend to be long. Acceleration techniques such as SENSE can be useful. k-t BLAST is a recent method employed to reduce scan times even further. However, these newer acceleration techniques may potentially degrade image quality; this could be overcome by using ah igher number of multicoil arrays. 4D k-t BLAST velocity mapping has not been extensively used (or validated) for cardiovascular applications. The aim of this study was to evaluate the performance of 4D flow-sensitive CMR in the thoracic aorta with 8- and 32-channel coil arrays using k-t BLAST, compared to SENSE acceleration.

Reproducibility of quantitative analysis of aortic 4D flow data

Background 3D cine phase-contrast CMR (4D Flow”) permits quantitative assessment of anomalous alterations of aortic blood flow. Two hemodynamic parameters that have been used for this purpose is the wall shear stress (WSS), which is known to regulate endothelial cell function, and the normalized flow displacement from the vessel center, which was recently shown to correlate with increased growth rates of ascending aortic dilation [1,2]. Analysis of these hemodynamic parameters requires that a user 1) positions a 2D plane of interest in the volumetric 4D Flow dataset and 2) delineates the contour of the vascular lumen in this 2D plane. We set out to assess the reproducibility of 4D Flow-based estimation of WSS and normalized flow displacement at these two critical levels of user-interaction. Furthermore, we assessed which of the parameters correlate best with aortic growth.