Velocity-encoded Magnetic Resonance Imaging Research Articles

Abstract 14595: Leveraging Deep Learning to Elucidate Subclinical Aortic Stenosis Risk

Background and Aims: Aortic stenosis (AS) is associated with a high global burden of morbidity. Current guidelines do not fully define normal aortic valve (AV) function or mild AS. We aimed to study normal variation in AV function and address current gaps in knowledge. Methods: We developed a deep learning model to study velocity-encoded magnetic resonance imaging (MRI) in 47,223 UK Biobank participants. We calculated aortic valve area (AVA), peak velocity (PV), and mean gradient (MG). Results: In healthy individuals, we found an annual decrement of 0.03 cm2 in AVA. Normal variation in AV function was predictive of future AV surgery (HR 2.4 per SD increase in PV, P2.6E-110), heart failure (HR 1.23 per SD, P=2.4E-07), and coronary disease (HR 1.23 per SD, P=2.0E-14). Risk was still elevated when excluding participants with moderate-to-severe AS. We determined thresholds for abnormal AV function as being >95% for all age groups in 31,909 healthy people. This established the boundary between normal variation and mild AS as any of: PV >1.65m/s, MG >4.9mmHg, and AVA <2.1cm2 (men) or <1.7cms2 (women). A total of 3,288 participants (7.0%) met the definition of mild AS which was associated with high risk for AV surgery (HR 57.2, P=4.4E-29). Over a mean 3.1±2.0 years of follow-up, the incidence of AV surgery was 0.02% in those with normal AV function and nearly 20% among participants with MG ≥10mmHg. Greater levels of ApoB, triglycerides, Lp(a), and inflammatory markers were associated with higher AV gradients. Conclusion: In this study, we report the largest analysis of AV function and cardiovascular disease in the general population with MRI using deep learning. We propose thresholds to define the lower bounds of mild AS and demonstrate a step change in cardiovascular risk between normal AV function and mild AS. Atherogenic and inflammatory biomarkers were associated with increased AV gradients. These findings may inform earlier surveillance and efforts to prevent complications of AS.

Impact of aortic stiffness by velocity-encoded magnetic resonance imaging on late gadolinium enhancement to predict cardiovascular events.

BackgroundIncreased aortic stiffness has been established as a marker in various cardiovascular diseases. Previous reports revealed a significant correlation between aortic stiffness and myocardial scarring using the late gadolinium enhancement cardiovascular magnetic resonance (LGE-CMR). However, prognostic data concerning aortic stiffness combining myocardial scarring remains limited.MethodA total of 402 patients who had undergone clinical CMR for the evaluation of cardiac function, LGE, and aortic pulse wave velocity (PWV) using velocity encoded-CMR (VE-CMR) were included. Patients were classified into 4 groups using mean PWV and the presence of LGE as elevated or non-elevated PWV and positive or negative LGE. Patients received follow-up for major adverse cardiovascular events (MACE) comprising cardiovascular death, non-fatal myocardial infarction, hospitalization for heart failure, coronary revascularization, and ischemic stroke. Predictors of MACE and hard cardiac events (cardiovascular death or non-fatal myocardial infarction) were evaluated.ResultsDuring the average follow-up period of 47.7 months, 58 MACE occurred. Patients who had elevated PWV and positive LGE experienced the highest rate of MACE compared to the group with non-elevated PWV and negative LGE (HR 11.90, p < 0.001). Among patients who had LGE, those who had elevated PWV experienced a 2.4-times higher rate of MACE compared to those who had non-elevated PWV. Multivariate analysis showed that PWV and LGE were independent predictors of MACE and hard cardiac events. PWV had excellent intra- and inter-observer reproducibility (intra-: ICC = 0.98, p < 0.001, inter-: ICC = 0.97, p < 0.001).ConclusionAortic stiffness using VE-CMR had prognostic value to predict cardiovascular events, with the added benefits of LGE.

P1830 Single-beat aortic arch pulse wave velocity by dual-gate simultaneous Doppler technique: a novel method for arterial stiffness evaluation

Abstract Background Guidelines recommend increased aortic stiffness as a negative prognostic factor to be considered in primary and secondary prevention. Pulse wave velocity (PWV) is a frequently employed surrogate marker of aortic stiffness. Carotid-femoral PWV is the most common index in research and clinical practice, but recently several velocity-encoded magnetic resonance imaging (MRI) techniques have been used for the evaluation of regional aortic arch PWV, where the stiffness seems to be particularly relevant from a prognostic point of view. Purposes. We developed a new ultrasound method for the assessment of aortic arch PWV, using a single-beat dual-gate simultaneous pulsed wave Doppler tracing. The aim of the study is to evaluate the feasibility of this new technique in a group of healthy volunteers. Methods We examined 126 healthy volunteers (81 females, 45 males, mean age 42 + 15 years, range 13-83 years) using a commercially available machine equipped with simultaneous dual-gate pulsed Doppler. Using the suprasternal approach, the first sample volume was placed in ascending aorta and the second one in descending aorta. The distance between the two sites was directly measured with a curvilinear tracing in the middle of the vessel, following the shape of the aortic arch. PWV was calculated as the ratio of distance (in millimiters) and the transit time (in milliseconds) measured using the "foot-to-foot" method. The results are then easily transformed, simplifying in the commonly unit of meters/second. Results Feasibility was 99%; in one case it was not possible to measure accurately the aortic arch PWV due to unfavorable suprasternal acustic window. The procedure time was very fast, requiring 2 + 1 minutes. Intraobserver and interobserver variability were 7% and 9% respectively. Aortic arch PWV, as expected, showed a strong correlation with age in males as well as in females (r= 0.71 and r = 0.60 respectively, p &amp;lt; 0.001 for both); there was also a significant correlation with body mass index (r = 0.31; p &amp;lt; 0.001). Aortic arch PWV values ranged from 3.1 to 8.5 m/s, showing a substantial overlap with normal values reported in MRI studies. Conclusions The direct measurement of aortic arch PWV is feasible and reproducible with ultrasound, using the novel single-beat dual-gate simultaneous pulsed wave Doppler tracing. This technique could be implemented in a standard echo examination, that is much more available than MRI studies. Further studies are needed to evaluate if Doppler-derived aortic arch PWV could provide additional prognostic information. Abstract P1830 Figure. Aortic Arch PWV

P3447Multimodal assessment and phenomapping of early atherosclerosis in children with chronic disease

Abstract Background Childhood survival of chronic disease steadily increased over the last decades. However, accumulating evidence suggests that survivors are at risk for early atherosclerosis. The “Cardiovascular Disease in Children with chronic disease” (CDC) study has two aims. First, multimodal assessment of early atherosclerosis was performed in adolescents with chronic inflammatory- and metabolic disorders in order to develop new diagnostic approaches. As fatty streak formation starts in the abdominal aorta, aortic wall thickness (AWT) and pulse wave velocity (PWV) were measured using cardiovascular magnetic resonance imaging (MRI), and compared with traditional carotid intima-media thickness (cIMT) and echocardiography. Second, comprehensive risk profiling was performed, including phenomapping of early risk factors, in order to establish cardiovascular risk profiles in childhood. Methods 113 adolescents aged 12–19 years old were enrolled*. The study population includes adolescents with juvenile idiopathic arthritis (JIA, n=19), cystic fibrosis (CF, n=24), obesity (n=20), corrected coarctation of the aorta (CoA, n=25), and corrected atrial septal defect as control group (ASD, n=25). The aorta was imaged on a 3.0 Tesla MR system using the 3D-T1-BB-VISTA sequence. Aortic PWV was assessed using velocity-encoded MRI. cIMT was measured in three directions for both the right- and left carotid artery using echography. Unbiased hierarchical clustering was performed on phenotypic data (phenomapping), including anthropomorphic-, metabolic-, and inflammatory parameters. Results* Aortic pulse wave velocity on MRI was highest in the obese group compared to controls (p=0.002), yet JIA patients (p=0.015), CoA patients (p=0.029), and CF patients (p=0.044) also showed increased PWV compared to controls. Aortic wall thickness was highest in obese adolescents (p=0.020) and in CF patients (p=0.043). cIMT was only increased in CoA patients (p=0.000). While PWV and AWT showed correlation with inflammatory- and metabolic parameters such as lymphocyte count (PWV, p=0.043), monocyte count (PWV, p=0.002; AWT, p=0.036), CRP (AWT, p=0.032), and QUICKI (PWV, p=0.026), cIMT correlated with systolic blood pressure (p=0.017). Phenomapping of risk factors will further define distinct cardiovascular risk profiles*. Conclusion Multimodal assessment of early atherosclerosis in children with chronic disease reveals differential vascular changes. While traditional cIMT is associated with increased systolic blood pressure in young CoA patients, aortic PWV and aortic wall thickness reflect early systemic inflammatory- and metabolic derangement. Phenomapping traditional risk factors alongside inflammatory- and metabolic parameters bears promise to establish early cardiovascular risk profiles in childhood chronic disease*. *Patient inclusion finishes May 2019, followed by phenomapping of patient characteristics. At the ESC, final data will be presented. Acknowledgement/Funding Wilhelmina Children's Hospital Research Fund, Dutch Topsector Life Sciences and Health TKI fund, Nutricia Research fund. HS was supported by VENI-NWO.

Abnormal aortic flow profiles persist after aortic valve replacement in the majority of patients with aortic valve disease: how model-based personalized therapy planning could improve results. A pilot study approach.

Complex blood flow profiles in the aorta are known to contribute to vessel dilatation. We studied flow profiles in the aorta in patients with aortic valve disease before and after surgical aortic valve replacement (AVR). Thirty-four patients with aortic valve disease underwent 4-dimensional velocity-encoded magnetic resonance imaging before and after AVR (biological valve = 27, mechanical valve = 7). Seven healthy volunteers served as controls. Eccentricity (ES) and complex flow scores (CFS) were determined from the degree of helicity, vorticity and eccentricity of flow profiles in the aorta. Model-based therapy planning was used in 4 cases to improve in silico postoperative flow profiles by personalized adjustment of size, rotation and angulation of the valve as well as aorta diameter. Patients with aortic valve disease showed more complex flow than controls [median ES 2.5 (interquartile range (IQR) 2.3-2.7) vs 1.0 (IQR 1.0-1.0), P < 0.001, median CFS 4.7 (IQR 4.3-4.8) vs 1.0 (IQR 1.0-2.0), P < 0.001]. After surgery, flow complexity in the total patient cohort was reduced, but remained significantly higher compared to controls [median ES 2.3 (IQR 1.9-2.3) vs 1.0 (IQR 1.0-1.0), P < 0.001, median CFS 3.8 (IQR 3.0-4.3) vs 1.0 (IQR 1.0-2.0), P < 0.001]. In patients after mechanical AVR, flow complexity fell substantially and showed no difference from controls [median ES 1.0 (IQR 1.0-2.3) vs 1.0 (IQR 1.0-1.0), P = 0.46, median CFS 1.0 (IQR 1.0-3.3) vs 1.0 (IQR 1.0-2.0), P = 0.71]. In all 4 selected cases (biological, n = 2; mechanical, n = 2), model-based therapy planning reduced in silico complexity of flow profiles compared to the existing post-surgical findings [median ES 1.7 (IQR 1.4-1.7) vs 2.3 (IQR 2.3-2.3); CFS 1.7 (IQR 1.4-2.5) vs 3.8 (IQR 3.3-4.3)]. Abnormal flow profiles in the aorta more frequently persist after surgical AVR. Model-based therapy planning might have the potential to optimize treatment for best possible individual outcome. clinicaltrials.gov NCT03172338, 1 June 2017, retrospectively registered; NCT02591940, 30 October 2015, retrospectively registered.

Atrial Fibrillation: Relationship between Left Atrial Pressure and Left Atrial Appendage Emptying Determined with Velocity-encoded Cardiac MR Imaging.

Purpose To investigate the relationship between left atrial appendage (LAA) blood flow determined with cardiac magnetic resonance (MR) imaging and left atrial pressure (LAP) estimated from invasive catheter measurements in patients with atrial fibrillation (AF). Materials and Methods This retrospective study was approved by the institutional review board, and patients provided written informed consent. Seventy-seven patients with AF (mean age, 57.8 years ± 9.8; range, 31-76 years) underwent cardiac MR imaging and catheter-based measurement of LAP, sequentially. Velocity-encoded (VENC) cardiac MR imaging was performed perpendicular to the ostium of the LAA. The maximum blood flux (in milliliters per second) from the LAA to the left atrium (LA) as determined with VENC MR imaging was defined as LAA emptying. Patients were classified into two groups: those with elevated LAP (peak LAP ≥19 mm Hg) and those with nonelevated LAP (peak LAP <19 mm Hg). Receiver operating characteristic curves were used to determine the cut-off values of LAA emptying in the assessment of the LAP status. Results LAA emptying showed a significantly inverse relationship (P < .01) with the peak LAP. Patients with elevated LAP showed significantly less LAA emptying than did patients with nonelevated LAP (mean, 39.3 mL/sec ± 13.7 vs 61.2 mL/sec ± 20.7, respectively; P < .01). In the assessment of elevated LAP with use of VENC MR imaging in normal sinus rhythm, the LAA emptying cut-off value of 47 mL/sec had a sensitivity of 75.0%, specificity of 87.5%, positive predictive value of 66.6%, and negative predictive value of 91.3%. At multivariate analysis, the odds ratio of low LAA emptying (<47 mL/sec) was independently associated with elevated LAP. Conclusion Evaluation of LAA emptying with use of VENC MR imaging is helpful for assessing the LAP status of patients with AF. © RSNA, 2017.

Endovascular MR-guided Renal Embolization by Using a Magnetically Assisted Remote-controlled Catheter System.

Purpose To assess the feasibility of a magnetically assisted remote-controlled (MARC) catheter system under magnetic resonance (MR) imaging guidance for performing a simple endovascular procedure (ie, renal artery embolization) in vivo and to compare with x-ray guidance to determine the value of MR imaging guidance and the specific areas where the MARC system can be improved. Materials and Methods In concordance with the Institutional Animal Care and Use Committee protocol, in vivo renal artery navigation and embolization were tested in three farm pigs (mean weight 43 kg ± 2 [standard deviation]) under real-time MR imaging at 1.5 T. The MARC catheter device was constructed by using an intramural copper-braided catheter connected to a laser-lithographed saddle coil at the distal tip. Interventionalists controlled an in-room cart that delivered electrical current to deflect the catheter in the MR imager. Contralateral kidneys were similarly embolized under x-ray guidance by using standard clinical catheters and guidewires. Changes in renal artery flow and perfusion were measured before and after embolization by using velocity-encoded and perfusion MR imaging. Catheter navigation times, renal parenchymal perfusion, and renal artery flow rates were measured for MR-guided and x-ray-guided embolization procedures and are presented as means ± standard deviation in this pilot study. Results Embolization was successful in all six kidneys under both x-ray and MR imaging guidance. Mean catheterization time with MR guidance was 93 seconds ± 56, compared with 60 seconds ± 22 for x-ray guidance. Mean changes in perfusion rates were 4.9 au/sec ± 0.8 versus 4.6 au/sec ± 0.6, and mean changes in renal flow rate were 2.1 mL/min/g ± 0.2 versus 1.9 mL/min/g ± 0.2 with MR imaging and x-ray guidance, respectively. Conclusion The MARC catheter system is feasible for renal artery catheterization and embolization under real-time MR imaging in vivo, and quantitative physiologic measures under MR imaging guidance were similar to those measured under x-ray guidance, suggesting that the MARC catheter system could be used for endovascular procedures with interventional MR imaging. (©) RSNA, 2016.

Aortic Arch Stiffness Is Associated With Incipient Brain Injury in Patients With Hypertension.

It has been shown that microstructural brain tissue damage can be detected in hypertension patients, while the underlying mechanisms are not fully understood. We aim to explore the association between diffusion tensor imaging (DTI) measures of brain injury and aortic arch pulse wave velocity (PWV) in hypertensive patients without clinically manifest cerebrovascular disease. Sixty-six hypertension patients (30 men, mean age 46±14 years) were prospectively included. Aortic arch PWV was assessed using velocity-encoded magnetic resonance imaging (VE-MRI). Brain tissue integrity was assessed by using DTI. Multivariable linear regression analysis was performed to assess the association between aortic arch PWV and fractional anisotropy (FA), axial diffusivity (AxD), and radial diffusivity (RD). Increased aortic arch PWV was associated with decreased white matter FA (β = -0.30, P = 0.018), increased gray matter AxD (β = 0.28, P = 0.016), and increased gray and white matter RD (β = 0.30, P = 0.008 and β = 0.35, P = 0.003, respectively). These effects were independent of age, sex, body mass index, smoking, and white matter hyperintensity (WMH) volume. Aortic arch stiffness relates to incipient brain injury before overt brain abnormalities may become apparent in patients with hypertension.

Mapping of spatial and temporal heterogeneity of plantar flexor muscle activity during isometric contraction: correlation of velocity-encoded MRI with EMG.

The aim of this study was to assess the correlation between contraction-associated muscle kinematics as measured by velocity-encoded phase-contrast (VE-PC) magnetic resonance imaging (MRI) and activity recorded via electromyography (EMG), and to construct a detailed three-dimensional (3-D) map of the contractile behavior of the triceps surae complex from the MRI data. Ten axial-plane VE-PC MRI slices of the triceps surae and EMG data were acquired during submaximal isometric contractions in 10 subjects. MRI images were analyzed to yield the degree of contraction-associated muscle displacement on a voxel-by-voxel basis and determine the heterogeneity of muscle movement within and between slices. Correlational analyses were performed to determine the agreement between EMG data and displacements. Pearson's coefficients demonstrated good agreement (0.84 < r < 0.88) between EMG data and displacements. Comparison between different slices in the gastrocnemius muscle revealed significant heterogeneity in displacement values both in-plane and along the cranio-caudal axis, with highest values in the mid-muscle regions. By contrast, no significant differences between muscle regions were found in the soleus muscle. Substantial differences among displacements were also observed within slices, with those in static areas being only 17-39% (maximum) of those in the most mobile muscle regions. The good agreement between EMG data and displacements suggests that VE-PC MRI may be used as a noninvasive, high-resolution technique for quantifying and modeling muscle activity over the entire 3-D volume of muscle groups. Application to the triceps surae complex revealed substantial heterogeneity of contraction-associated muscle motion both within slices and between different cranio-caudal positions.

Effects of contour propagation and background corrections in different MRI flow software packages.

BackgroundVelocity-encoded magnetic resonance imaging (VENC-MRI) is a commonly used technique in cardiac examinations. This technique utilizes the phase shift properties of protons moving along a magnetic field gradient. VENC-MRI offers a unique way of measuring the severity of valve regurgitation by directly quantifying the regurgitation flow volume.PurposeTo compare flow analysis results of different software programs and to assess the effect of background correction in sample patient cases.Material and MethodsA phantom was built out of Polymethyl methacrylate (PMMA) which provides tubes of different diameters. These tubes can be connected to an external water circuit to generate a water flow inside the tubes. Expected absolute flow quantities inside the tubes were determined from preset tube- and flow-parameters. Different flow conditions were measured with a VENC-MRI sequence and the images evaluated using different software packages. In a second step six randomly selected patients showing different degrees of aortic insufficiency were evaluated in clinical terms.ResultsThe contour propagation algorithms used in the software packages performed differently even on static phantom geometry. In terms of clinical evaluation the software packages performed similarly. Enabling background correction or leaving out manual correction of propagated contours changed results for severity of aortic insufficiency.ConclusionTurning on background correction and manual correction of propagated contours in MRI flow volume measurements is strongly recommended.

Characterization of the discrepancies between four-dimensional phase-contrast magnetic resonance imaging and in-silico simulations of cerebrospinal fluid dynamics.

The purpose of the present study was to compare subject-specific magnetic resonance imaging (MRI)-based computational fluid dynamics (CFD) simulations with time-resolved three-directional (3D) velocity-encoded phase-contrast MRI (4D PCMRI) measurements of the cerebrospinal fluid (CSF) velocity field in the cervical spinal subarachnoid space (SSS). Three-dimensional models of the cervical SSS were constructed based on MRI image segmentation and anatomical measurements for a healthy subject and patient with Chiari I malformation. CFD was used to simulate the CSF motion and compared to the 4D PCMRI measurements. Four-dimensional PCMRI measurements had much greater CSF velocities compared to CFD simulations (1.4 to 5.6× greater). Four-dimensional PCMRI and CFD both showed anterior and anterolateral dominance of CSF velocities, although this flow feature was more pronounced in 4D PCMRI measurements compared to CFD. CSF flow jets were present near the nerve rootlets and denticulate ligaments (NRDL) in the CFD simulation. Flow jets were visible in the 4D PCMRI measurements, although they were not clearly attributable to nerve rootlets. Inclusion of spinal cord NRDL in the cervical SSS does not fully explain the differences between velocities obtained from 4D PCMRI measurements and CFD simulations.

Disturbed left ventricular inflow and ejection pattern in corrected atrioventricular septal defect patients assessed by 4DFlow MRI and particle tracing

Background The normal pattern of left ventricular (LV) inflow and ejection of affects the efficiency of cardiac pumping performance. Altered inflow direction due to a corrected atrioventricular septal defect (AVSD) may disturb this pattern leading to decreased efficiency. We aimed to quantitatively describe the LV blood flow pattern using 4-dimensional velocity-encoded cardiac magnetic resonance imaging (4DFlow MRI) and particle tracing in healthy volunteers and corrected AVSD patients.

Invited Commentary

Invited Commentary

Aortic stiffness is associated with white matter integrity in patients with type 1 diabetes.

To assess the association between aortic pulse wave velocity (PWV) as a marker of arterial stiffness and diffusion tensor imaging of brain white matter integrity in patients with type 1 diabetes using advanced magnetic resonance imaging (MRI) technology. Forty-one patients with type 1 diabetes (23 men, mean age 44 ± 12 years, mean diabetes duration 24 ± 13 years) were included. Aortic PWV was assessed using through-plane velocity-encoded MRI. Brain diffusion tensor imaging (DTI) measurements were performed on 3-T MRI. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were calculated for white and grey matter integrity. Pearson correlation and multivariable linear regression analyses including cardiovascular risk factors as covariates were assessed. Multivariable linear regression analyses revealed that aortic PWV is independently associated with white matter integrity FA (β = -0.777, p = 0.008) in patients with type 1 diabetes. This effect was independent of age, gender, mean arterial pressure, body mass index, smoking, duration of diabetes and glycated haemoglobin levels. Aortic PWV was not significantly related to grey matter integrity. Our data suggest that aortic stiffness is independently associated with reduced white matter integrity in patients with type 1 diabetes. Aortic stiffness is associated with brain injury. Aortic stiffness exposes small vessels to high pressure fluctuations and flow. Aortic stiffness is associated with microvascular brain injury in diabetes. This suggests a vascular contribution to early subtle microstructural deficits.

Quantitative Measurements of Cerebral Circulation in Spontaneously Regressing Traumatic Carotid-Cavernous Sinus Fistula with Velocity-Encoded Magnetic Resonance Imaging

and quantitative evidence for whether endovascular occlusion would remove the shunts connected to extradural venous drainage alone, or further resolve the disturbance of cerebral venous flow. It is not known how cerebral vessels would change in the long-term as a result of obstructing this shunt flow, or how the clinical symptoms are related to the haemodynamic changes in the rare cases of spontaneous regression. The understanding of the pathophysiology of CCF can be enhanced by correlating the clinical symptoms and MRI findings during a long observational period. Velocity-encoded magnetic resonance imaging (VENCMRI) has shown excellent diagnostic accuracy and reliability for the measurement of the flow volumes (FVs) in cerebral vessels [12]. Furthermore, VENC-MRI does not require contrast medium administration or invasive catheterization, and is considered a safe and appropriate followup imaging technique [13]. However, this tool has never been used for quantifying the shunt volume and cerebral circulation related to CCF. A case in which VENC-MRI was used to measure the shunt volume of and FVs in the cerebral vessels in a direct CCF patient is presented herein. The temporal changes during spontaneous regression are demonstrated, and the relationships between the patient’s clinical symptoms and the measured cerebral haemodynamics are discussed.

Measuring Wall Shear Stress Using Velocity-Encoded MRI

This study reviews the application of velocity-encoded magnetic resonance imaging (MRI) for the calculation of wall shear stress (WSS). The basics of velocity-encoded MRI and WSS are reviewed and calculation methods for estimation of the WSS from 2D or 3D (cine) velocity-encoded MRI data are presented. In recent years, there has been a trend towards 3D WSS quantification methods. Current clinical applications of WSS are discussed, including an overview of estimated WSS magnitudes in different patient groups at multiple anatomical locations (aorta, carotid arteries, and intracranial aneurysms). A large variation was found between different WSS calculation methods. The future of MRI-based WSS calculations depends on its prognostic and diagnostic value, both of which need to be further explored in clinical studies. In this context, both further improvement of the quality of velocity-encoded MRI data and scan time reduction are pivotal.

Impact of respiration on stroke volumes in paediatric controls and Fontan patients assessed by MR real-time phase velocity mapping

Background Routine blood volume quantification is generally performed by using two-dimensional velocity-encoded phase-contrast magnetic resonance imaging (PC-MRI). Due to their long acquisition times averaging of flow information occur leading to underestimation of peak velocities and preventing the examination of respirationrelated stroke volume (SV) variations. Methods Non-electrocardiographic triggered real-time PC-MRI using EPI combined with half-Fourier technique (TR/ TEeff/excitation angle = 12-14 ms/3.3 ms/40°, SENSEfactor = 4, temporal resolution = 24-28 ms) was applied to study respiration-driven SV fluctuations in the ascending aorta (AAo) and both caval veins (SVC, IVC) under natural and forced breathing in 34 healthy children and 10 pediatric Fontan patients. Data were collected during a 12-14 s time interval. The subject’s physiological data (ECG & respiration) were recorded simultaneously for matching with flow data. Virtual stroke volumes were generated dividing the respiration curve in four segments: expiration, breathing in, inspiration and breathing out. Spirometric measurements were performed to validate respiratory volumes. Statistical differences were analyzed by using ANOVA, paired Student t-test and Bland-Altman statistics. Results Stroke volume variability in healthy subjects was around 6% for AAo and >15% for SVC and IVC while breathing naturally. Under forced breathing variability increased to 9% and >34%, respectively. In Fontan patients a two to three-fold augmentation was observed in both respiratory maneuvers. Whereas in volunteers aortic SV was elevated during expiration (6%) and decreased during inspiration (-6%) in relation to mean respiratory SV, highest blood flow was detected during breathing in SVC (10%) and IVC (20%) and lowest blood flow during breathing out (-12%, -15%). Differences were increased under forced breathing. All differences were statistically significant. Regarding patients SV variability was drastically increased and had to be related to the patient’s individual quality of Fontan circulation. Intraobserver and interobserver varability of the four separated respiration-dependent SV was below 5%. Conclusions Due to its non-averaging character real-time PC-MRI allows a physiological assessment of respiratory-related SV fluctuations in healthy subjects as well as in Fontan patients and demonstrates its capability for detection of short-term effects in clinical routine work. It can be expected that real-time PC-MRI has the potential to classify the quality of Fontan hemodynamics. Funding None.

CMR assessment of right ventricular function in patients with combined pulmonary stenosis and insufficiency after correction of tetralogy of Fallot

Tetralogy of Fallot (TOF) is one of the most common types of congenital heart disease and requires prompt surgical correction. Post-correction pulmonary insufficiency (PI) often ensues in adulthood. At times, the PI is accompanied by residual pulmonary stenosis (PS). Little is known regarding right ventricular (RV) function in the setting of combined PS and PI. To compare cardiac magnetic resonance (CMR) parameters for the assessment of RV function between patients with combined pulmonary stenosis and pulmonary insufficiency (PSPI) and isolated PI following surgical repair of TOF. Retrospective review of patients with comparable corrected TOF and similar PI was performed. Seventeen patients (median age, 24 years; range, 10-52 years) had combined PSPI and 30 patients (median age, 30 years; range, 6-70 years) had isolated PI. Cine magnetic resonance (MR) images (Philips Medical Systems, Best, The Netherlands) in the short-axis plane were used to calculate end-systolic, end-diastolic, and stroke volumes (RVESV, RVEDV, RVSV) and to measure RV wall thickness. Velocity-encoded cine MR images were used to measure pulmonary regurgitation fraction (PRF) by calculating the ratio of backward flow and total forward flow, obtained from the main pulmonary flow analysis. Peak pressure gradient across the pulmonary valve was obtained from spectral Doppler echocardiography. RVEF was 51 ± 8% in the PSPI patients and 39 ± 11%, in the patients with isolated PI (P = 0.001). Additionally, RV wall thickness was 5.2 ± 0.8 mm in the PSPI patients compared to 2.6 ± 0.9 mm in the isolated PI patients (P = 0.001). RVESVi and RVEDVi were significantly lower (P < 0.05) in patients with combined PSPI (60 ± 21 mL/m(2), 121 ± 35 mL/m(2), respectively) compared to the patients with isolated PI (95 ± 48 mL/m(2), 152 ± 61 mL/m(2), respectively). RV function is preserved in patients with PSPI when compared to patients with PI following surgical repair of TOF.

Pulse wave velocity and flow in the carotid artery versus the aortic arch: Effects of aging

To explore differences in arterial stiffness of the aorta and carotid artery, assessed by pulse wave velocity (PWV), to evaluate the blood flow volume distribution towards the carotid circulation and to assess the effect of aging on the coupling between aortic and carotid PWV using velocity-encoded magnetic resonance imaging (MRI). Sixteen adult younger volunteers (age <30 years) and 16 older volunteers (age >45 years) underwent 3T MRI examination to assess aortic and carotid flow volumes and PWV using the transit time method. Aortic versus carotid PWV-ratio was 1.2 for younger volunteers and 0.95 for older volunteers, demonstrating leveling of wall stiffness. Furthermore, flow volume per minute in the internal carotid artery was lower for older versus younger volunteers (mean volume 177 ± 42 mL/min/m(2) vs. 147 ± 32 mL/min/m(2), P = 0.028), whereas aorta and common carotid artery flow volumes were not different. Consequently, the fraction of blood flow volume towards the brain was smaller for older versus younger volunteers (61 ± 9% versus 71 ± 8%, P = 0.002). PWV-leveling between aorta and carotid artery at older age is associated with a reduction in blood flow volume towards the brain. Velocity-encoded MRI can be used to evaluate PWV and flow volume distribution in the aortic arch and the carotid circulation.

Arterial, Venous, and Cerebrospinal Fluid Flow: Simultaneous Assessment with Bayesian Multipoint Velocity-encoded MR Imaging

To measure arterial, venous, and cerebrospinal fluid (CSF) velocities simultaneously by using Bayesian multipoint velocity-encoded magnetic resonance (MR) imaging and to compare interacquisition reproducibility relative to that of standard phase-contrast MR imaging for sequential measurements of arterial, venous, and CSF velocities. This study was approved by the local ethics committee, and informed consent was obtained from all subjects. Simultaneous measurement of blood and CSF flow was performed at the C1-C2 level in 10 healthy subjects (mean age, 24.4 years ± 2.7; five men, five women) by using accelerated Bayesian multipoint velocity-encoded MR imaging. Data were compared with those obtained from two separate conventional phase-contrast MR imaging acquisitions, one optimized for arterial and venous blood flow (velocity encoding range, ±50 cm/sec) and the other optimized for CSF flow (velocity encoding range, ±10 cm/sec), with an imaging time of approximately 2 minutes each. Data acquisition was repeated six times. Intraclass correlation coefficient (ICC) and linear regression were used to quantify interacquisition reproducibility. There was no significant difference in arterial blood flow measured with Bayesian multipoint velocity-encoded MR imaging and that measured with phase-contrast MR imaging (mean ICC, 0.96 ± 0.03 vs 0.97 ± 0.02, respectively). Likewise, there was no significant difference between CSF flow measured with Bayesian multipoint velocity-encoded MR imaging and that measured with phase-contrast MR imaging (mean ICC, 0.97 ± 0.02 vs 0.96 ± 0.05, respectively). For venous blood flow, the ICC with Bayesian multipoint MR imaging was significantly larger than that with conventional phase-contrast MR imaging (mean, 0.75 ± 0.23 vs 0.65 ± 0.26, respectively; P = .016). Bayesian multipoint velocity-encoded MR imaging allows for simultaneous assessment of fast and slow flows in arterial, venous, and CSF lumina in a single acquisition. It eliminates the need for vessel-dependent adjustment of the velocity-encoding range, as required for conventional sequential phase-contrast MR imaging measurements.