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Introduction: The aim of this study was to evaluate the feasibility of identifying the fetal cardiac and thoracic vascular structures with non-gated dynamic balanced steady-state free precession (SSFP) MRI sequences. Methods: We retrospectively assessed the visibility of cardiovascular anatomy in 60 fetuses without suspicion of congenital heart defect. Non-gated dynamic balanced SSFP sequences were acquired in three anatomic planes of the fetal thorax. The images were analyzed following a segmental approach in consensus reading by an experienced pediatric cardiologist and radiologist. An imaging score was defined by giving one point to each visualized structure, yielding a maximum score of 21 points. Image quality was rated from 0 (poor) to 2 (excellent). The influence of gestational age (GA), field strength, placenta position, and maternal panniculus on image quality and imaging score were tested. Results: 30 scans were performed at 1.5T, 30 at 3T. Heart position, atria, and ventricles could be seen in all 60 fetuses. Basic diagnosis (>12 points) was achieved in 54 cases. The mean imaging score was 16.8+/−3.8. Maternal panniculus (r = −0.3; p = 0.015) and GA (r = 0.6; p < 0.001) correlated with imaging score. Field strength influenced image quality, with 1.5T being better than 3T images (p = 0.012). Imaging score or quality was independent of placenta position. Conclusion: Fetal cardiac MRI with non-gated SSFP sequences enables recognition of basic cardiovascular anatomy.

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. Electronic supplementary material The online version of this article (10.1007/s00247-020-04885-w) contains supplementary material, which is available to authorized users.

Funding Acknowledgements Type of funding sources: None. Purpose We sought to retrospectively evaluate the feasibility of identifying the fetal cardiac and thoracic vascular structures with non-gated dynamic balanced steady-state free precession MRI sequences. Methods We retrospectively assessed the visibility of cardiovascular anatomy in 66 fetuses without suspicion of congenital heart defect (mean gestational age 27+/- 4, range 21-38 weeks). Non-gated dynamic balanced steady-state free precession (SSFP) sequences were acquired in three planes (axial, coronal and sagittal) of the fetal thorax (slice thickness 4-5mm, FOV 400, FA 60°, matrix 256x256). The images were analysed following a segmental approach in consensus reading by an experienced paediatric cardiologist and radiologist. An imaging score was defined by giving one point to each visualized structure. Basic diagnostic structures included the atria, ventricles, systemic veins, right and left ventricular outflow tracts (RVOT/LVOT), aortic arch, descending aorta (DAO), ductus arteriosus and thymus (12 points); advanced diagnostic features included the atrioventricular (AV) valves, pulmonary arteries and veins, supraaortic arteries and trachea, yielding a maximum score of 21 points. Image quality was rated from 0 (poor) to 2 (good). The influence of gestational age (GA), field strength, placenta position, and maternal panniculus on image quality and imaging score were tested. Results 34 scans were performed at 1.5 T, 32 at 3 T. Heart position, atria and ventricles could be seen in all 66 fetuses. Basic diagnosis (>12 points) was achieved in 60 (90%) cases, with visualization of the IVC and SVC in 65 (98%) and 63 (95%), RVOT in 62 (94%), LVOT in 61 (92%), aortic arch in 60 (91%), DAO in 64 (97%), ductus arteriosus in 59 (89%) and thymus in 50 (76%) fetuses. The AV valves were recognised in 55 (83%), the pulmonary arteries in 35 (53%), at least one pulmonary vein in 46 (70%), the supraaortic arteries in 42 (64%), and the trachea in 59 (89%) fetuses. The mean imaging score was 16.8 +/- 3.7. Maternal panniculus (r -0.3; p 0.01) and gestational age (r 0.6; p < 0.001) correlated with imaging score. Field strength influenced image quality, with 1.5 T being better than 3T images (p 0.04), but not the total imaging score. Imaging score or quality were independent from placenta position. Conclusions Fetal heart MRI with a non-gated SSFP sequence in multiple planes enables recognition of basic cardiovascular anatomy. Advanced diagnostics may be limited by thick maternal panniculus, lower GA and higher field strength.

Children with orofacial deformity may require repeated imaging of the facial skeleton.To test the feasibility and accuracy of "black bone" magnetic resonance imaging (MRI) for assessing facial deformity in children.Three-dimensional (3-D) black bone gradient echo sequences (flip angle 5°, submillimetre spatial resolution) from 10 children (median age: 13 years, range: 2-16 years), who underwent MRI of the temporomandibular joints, were evaluated with multiplanar reconstruction and 3-D rendering tools. Intra- and inter-reader agreement was investigated for measuring the height of the mandibular ramus and condyle, basal length of the mandible, gonion angle and mandibular inclination angle by intraclass correlation coefficient (ICC) and Bland-Altman analysis. Absolute percentage error was calculated with the average of all measurements serving as reference.Sixty linear and 40 angle measurements were obtained on reformatted multiplanar black bone images with excellent inter-reader agreement (ICC 0.99, agreement bias 1.4 mm/ 1.5°) and small error (median absolute error 3%). The black bone images required inversion of the signal intensity and removal of air before they could be processed with standard volume rendering tools. The diagnostic utility of 3-D views for assessing the facial skeleton was sufficient except for assessing dental relationship.Morphometric measurements of the mandible can be obtained from black bone MRI with comparable inter-rater agreement to that reported for cone beam computed tomography (CT). With improvements of 3-D rendering techniques and software, black bone MRI may become a radiation-free alternative to CT in children with facial deformities.

Objectives To use 4D-flow MRI to describe systemic and non-systemic ventricular flow organisation and energy loss in patients with repaired d-transposition of the great arteries (d-TGA) and normal subjects. Methods Pathline tracking of ventricular volumes was performed using 4D-flow MRI data from a 1.5-T GE Discovery MR450 scanner. D-TGA patients following arterial switch (n = 17, mean age 14 ± 5 years) and atrial switch (n = 15, 35 ± 6 years) procedures were examined and compared with subjects with normal cardiac anatomy and ventricular function (n = 12, 12 ± 3 years). Pathlines were classified by their passage through the ventricles as direct flow, retained inflow, delayed ejection flow, and residual volume and visually and quantitatively assessed. Additionally, viscous energy losses (ELv) were calculated. Results In normal subjects, the ventricular flow paths were well ordered following similar trajectories through the ventricles with very little mixing of flow components. The flow paths in all atrial and some arterial switch patients were more irregular with high mixing. Direct flow and delayed ejection flow were decreased in atrial switch patients’ systemic ventricles with a corresponding increase in residual volume compared with normal subjects (p = 0.003 and p < 0.001 respectively) and arterial switch patients (p < 0.0001 and p < 0.001 respectively). In non-systemic ventricles, arterial switch patients had increased direct flow and decreased delayed ejection fractions compared to normal (p = 0.007 and p < 0.001 respectively) and atrial switch patients (p = 0.01 and p < 0.001 respectively). Regions of high levels of mixing of ventricular flow components showed elevated ELv. Conclusions 4D-flow MRI pathline tracking reveals disordered ventricular flow patterns and associated ELv in d-TGA patients. Key Points • 4D-flow MRI can be used to assess intraventricular flow dynamics in d-TGA patients. • d-TGA arterial switch patients mostly show intraventricular flow dynamics representative of normal subjects, while atrial switch patients show increased flow disorder and different proportions of intraventricular flow volumes. • Flow disruption and disorder increase viscous energy losses.

Treatment of heart failure with preserved ejection fraction (HFpEF) remains a major unmet medical need. An implantable valveless pulsatile pump with a single cannula—the CoPulse pump—may provide beneficial hemodynamic support for select HFpEF patients when connected to the failing ventricle. We aimed to demonstrate hemodynamic efficacy and hemocompatible design feasibility for this novel assist device. The hemodynamic effect of the pump was investigated with an in vitro circulatory mock loop and an ex vivo isolated porcine heart model. The hydraulic design was optimized using computational fluid dynamics (CFD), and validated by 4D-flow magnetic resonance imaging (MRI). The pump reduced left atrial pressure (> 27%) and increased cardiac output (> 14%) in vitro. Ex vivo experiments revealed elevated total stroke volume at increased end-systolic volume during pump support. Asymmetric cannula positioning indicated superior washout, decreased stagnation (8.06 mm2 vs. 31.42 mm2), and marginal blood trauma potential with moderate shear stresses ( 0.76). The CoPulse pump proved hemodynamically effective. Hemocompatibility metrics were comparable to those of a previously reported, typical pulsatile pump with two cannulae. The encouraging in vitro, ex vivo, and hemocompatibility results substantiate further development of the CoPulse pump., Annals of Biomedical Engineering, 48, ISSN:1573-9686, ISSN:0191-5649, ISSN:0090-6964

Wall shear stress (WSS) plays a governing role in vascular remodeling and a pathogenic role in vessel wall diseases. However, little is known of the normal WSS patterns in the aorta as there is currently no practical means to routinely measure WSS and no normal ranges derived from population data exist. WSS measurements were made on the aorta of 224 subjects with normal anatomy using four-dimensional flow MRI with multiple encoding velocities and an optimized postprocessing routine. The spatial and temporal variation in WSS and oscillatory shear index was analyzed using a flat map representation of the unfolded aorta. The influence of aortic shape and velocity on WSS was evaluated using regression analysis. WSS in the thoracic aorta is dominated by axial flow. Average peak systolic WSS was 1.79 ± 0.71 Pa in the aortic arch and was significantly higher at 2.23 ± 1.04 Pa in the descending aorta, with a strong negative correlation with advancing age. The spatial distribution of WSS is highly heterogeneous, with a localized region of elevated WSS along the length of the anterior wall seen across all individuals. Our data demonstrate that accurate four-dimensional flow-derived WSS measurement is feasible, and we further provide a standardized parametric approach for presentation and analysis. We present a normal range for WSS across the lifespan, demonstrating a decrease in WSS with advancing age as well as illustrating the high degree of spatial and temporal variation. NEW & NOTEWORTHY With the use of four-dimensional flow MRI and postprocessing, accurate direct measurement of wall shear stress (WSS) was performed in a population of normal thoracic aortas ( n = 224). WSS was higher in the descending aorta compared with the aortic arch and decreased with age. A heterogeneous pattern of elevated WSS along the length of the aorta anterior wall was consistent across the population. This work provides normal data across the adult age range, permitting comparison with pathology.

Background Abnormal flow dynamics play an early and causative role in pathologic changes of the ascending aorta. Purpose To identify: 1) the changes in flow, shape, and size that occur in the ascending aorta with normal human ageing and 2) the influence of these factors on aortic flow dynamics. Study type Retrospective. Subjects In all, 247 subjects (age range 19-86 years, mean 49 ± 17.7, 169 males) free of aortic or aortic valve pathology were included in this study. Subjects were stratified by youngest (18-33 years; n = 64), highest (>60 years, n = 67), and the middle two quartiles (34-60 years, n = 116). Field strength/sequence Subjects underwent a cardiac MRI (3T) exam including 4D-flow MRI of the aorta. Assessment Aortic curvature, arch shape, ascending aortic angle, ascending aortic diameter, and the stroke volume normalized by the aortic volume (nSV) were measured. Velocity, vorticity, and helicity were quantified across the thoracic aorta. Statistical tests Univariate and multivariate regressions were used to quantify continuous relationships between variables. Results Aortic diameter, ascending aortic angle, shape, and curvature all increased across age while nSV decreased (all P 10 times that of diameter and other shape factors. Data conclusion Aortic shape influences flow dynamics in younger subjects. Flow conditions become increasingly disturbed with advancing age, and in these conditions nSV has a more dominant effect on flow patterns than shape factors. Level of evidence 3 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:90-100.

Peripheral veno-arterial extra-corporeal membrane oxygenation (ECMO) is an artificial circulation that supports patients with severe cardiac and respiratory failure. Differential hypoxia during ECMO support has been reported, and it has been suggested that it is due to the mixing of well-perfused retrograde ECMO flow and poorly-perfused antegrade left ventricle (LV) flow in the aorta. This study aims to quantify the relationship between ECMO support level and location of the mixing zone (MZ) of the ECMO and LV flows. Steady-state and transient computational fluid dynamics (CFD) simulations were performed using a patient-specific geometrical model of the aorta. A range of ECMO support levels (from 5% to 95% of total cardiac output) were evaluated. For ECMO support levels above 70%, the MZ was located in the aortic arch, resulting in perfusion of the arch branches with poorly perfused LV flow. The MZ location was stable over the cardiac cycle for high ECMO flows (>70%), but moved 5cm between systole and diastole for ECMO support level of 60%. This CFD approach has potential to improve individual patient care and ECMO design.

Imaging-based evaluation of cardiac structure and function remains paramount in the diagnosis and monitoring of congenital heart disease in childhood. Accurate measurements of intra- and extracardiac hemodynamics are required to inform decision making, allowing planned timing of interventions prior to deterioration of cardiac function. Four-dimensional flow magnetic resonance imaging is a nonionizing noninvasive technology that allows accurate and reproducible delineation of blood flow at any anatomical location within the imaging volume of interest, and also permits derivation of physiological parameters such as kinetic energy and wall shear stress. Four-dimensional flow is the focus of a great deal of attention in adult medicine, however, the translation of this imaging technique into the pediatric population has been limited to date. A more broad-scaled application of 4-dimensional flow in pediatric congenital heart disease stands to increase our fundamental understanding of the cause and significance of abnormal blood flow patterns, may improve risk stratification, and inform the design and use of surgical and percutaneous correction techniques. This paper seeks to outline the application of 4-dimensional flow in the assessment and management of the pediatric population affected by congenital heart disease.

44th Congress of the Société de Biomécanique, Poitiers, FRANCE, 28-/10/2019 - 30/10/2019; The motivation to focus on coherent structure detection in cardiovascular systems is two-fold: 1) the ability to reliably detect abnormal inefficient flow patterns from a normal optimal state; and 2) the detection of flow conditions conducive to secondary pathological processes such as thrombosis - as the coherent structures are thought to perform an important role in avoiding stasis by ?washing out' the cardiac cavities (e.g. the atrial appendage or LV apex; Birdwell et al. 1978). Detection of the coherent structures could be performed using a number of different vorticity criteria, such as: threshold of vorticity magnitude, Q-criterion and ?2-criterion. However, prior application and evaluation of these different criteria in the cardiovascular system by 3D?+?t phase contrast (PC) flow MRI is limited as most approaches have used ?2- or Q-criteria (Elbaz et al. 2014) without comparison with other approaches. There is therefore a need to more broadly assess the capacity of these criteria to detect and describe coherent structures. Initial work by Garcia et al. (2013), reported the influence of noise and the spatial resolution of helicity. An alternative approach using data clustering has been reported by Wong et al. (2010). The primary aim of this work is to compare criteria for the assessment of coherent structures in the left ventricle by 3D?+?t PC flow MRI in healthy volunteers. To investigate the influence of diastolic function on the coherent structures in healthy volunteers detected by different criteria (vorticity, Q- or ?2-criteria) is the second aim of this work.

PURPOSE To analyze the dependence of flow volume measurements on 3D cine phase-contrast MRI (4D-flow MRI) background phase correction. METHODS In 31 subjects scanned on a 1.5T MRI scanner, flow volume measurements at 4 vessels were made using phantom corrected 2D phase contrast and 4D flow with background phase correction performed by linear, second, third, and fourth-order polynomial fitting to static tissue. Variations in the amount and distribution of static tissue were made to investigate the influence on flow volume measurements. RESULTS Bland Altman comparison of 2D phase-contrast and 4D-flow measurements showed low bias (2.3%-4.8%) and relatively large limits of agreement (13.5%-17.6%). Approximately half of this was attributable to sequence and physiological differences between the 2 scan sequences, demonstrated by smaller limits of agreement (5.3%-10.0%) when comparing 4D-flow measurements with differing background phase corrections. Using only 20% of available static tissue points for polynomial fitting resulted in only 1% difference in flow volume measurements. Using asymmetrically distributed static tissue or including nonstatic tissue for polynomial fitting yielded highly variable differences in flow volume measurements, which became more variable with increased polynomial order. Completely asymmetric static tissue selection resulted in high deviations in flow volume measurements (mean > 7%, max = 345%). CONCLUSION Comparisons between 2D phase-contrast and 4D-flow volume measurements should consider influences from sequence and physiological differences. A subset of static tissue points may be used with low impact on flow measurements, but should avoid the inclusion of nonstatic tissue and avoid asymmetric distribution. Higher-order polynomial fits are more susceptible to inaccurate static tissue selection.

The hippocampus is a key component of emotional and memory circuits and is broadly connected throughout the brain. We tracked the whole-brain connections of white matter fibres from the hippocampus using ultra-high angular resolution diffusion MRI in both a single 1150-direction dataset and a large normal cohort (n = 94; 391-directions). Using a connectomic approach, we identified six dominant pathways in terms of strength, length and anatomy, and characterised them by their age and gender variation. The strongest individual connection was to the ipsilateral thalamus. There was a strong age dependence of hippocampal connectivity to medial occipital regions. Overall, our results concur with preclinical and ex-vivo data, confirming that meaningful in vivo characterisation of hippocampal connections is possible in an individual. Our findings extend the collective knowledge of hippocampal anatomy, highlighting the importance of the spinal-limbic pathway and the striking lack of hippocampal connectivity with motor and sensory cortices.

PURPOSE 4D-flow MRI obtains a time-dependent 3D velocity field; however, its use for the calculation of higher-order parameters is limited by noise. We present an algorithm for denoising 4D-flow data. THEORY AND METHODS By integrating a velocity field and eliminating streamlines in noisy flow, depicted by high curvature, a denoised dataset may be extracted. This method, defined as the velocity field improvement (VFIT) algorithm, was validated in an analytical dataset and using in vivo data in comparison with a computation fluid dynamics (CFD) simulation. As a proof of principal, wall shear stress (WSS) measurements in the descending aorta were compared with those defined by CFD. RESULTS The VFIT algorithm achieved a >100% noise reduction of a corrupted analytical dataset. In addition, 4D-flow data were cleaned to show improved spatial resolution and near wall velocity representation. WSS measures compared well with CFD data and bulk flow dynamics were retained (

Purpose To quantitatively characterize the central role of vortex formation on the flow patterns and energy transfer within the right atrium (RA). Materials and Methods 4D-flow magnetic resonance imaging (MRI) data with multiple encoding velocities was acquired in 12 healthy subjects at 3T. Particles entering the RA were classified according to the origin of entry. Vortex membership was numerically derived by assessing the location of pathline center of curvature relative to the vortex core, defined by Q-criteria. Flow dynamics and energetics were assessed using paired t-tests. Results The majority of flow (74%) passes through the RA in a single beat, with a very small volume fraction retained longer than two beats (

Diffusion MRI (dMRI) tractography is a uniquely powerful tool capable of demonstrating structural brain network abnormalities across a range of psychiatric disorders; however, it is not currently clinically useful. This is because limitations on sensitivity effectively restrict its application to scientific studies of cohorts, rather than individual patients. Recent improvements in dMRI hardware, acquisition, processing and analysis techniques may, however, overcome these measurement limitations. We therefore acquired the highest-ever angular resolution in vivo tractographic data set, and used these data to ask the question: 'is cutting-edge, optimised dMRI now sensitive enough to measure brain network abnormalities at a level that may enable personalised psychiatry?' The fibre tracking performance of this 'gold standard' data set of 1150 unique directions (11 shells) was compared to a conventional 64-direction protocol (single shell) and a clinically practical, highly optimised and accelerated 9-min protocol of 140 directions (3 shells). Three major tracts of relevance to psychiatry were evaluated: the cingulate bundle, the uncinate fasciculus and the corticospinal tract. We found up to a 34-fold improvement in tracking accuracy using the 1150-direction data set compared to the 64-direction data set, while 140-direction data offered a maximum 17-fold improvement. We also observed between 20 and 50% improvements in tracking efficiency for the 140-direction data set, a finding we then replicated in a normal cohort (n = 53). We found evidence that lower angular resolution data may introduce systematic anatomical biases. These data highlight the imminent potential of dMRI as a clinically meaningful technique at a personalised level, and should inform current practice in clinical studies.

Abnormal flow dynamics play an early and causative role in pathologic changes of the ascending aorta.To identify: 1) the changes in flow, shape, and size that occur in the ascending aorta with normal human ageing and 2) the influence of these factors on aortic flow dynamics.Retrospective.In all, 247 subjects (age range 19-86 years, mean 49 ± 17.7, 169 males) free of aortic or aortic valve pathology were included in this study. Subjects were stratified by youngest (18-33 years; n = 64), highest (60 years, n = 67), and the middle two quartiles (34-60 years, n = 116).Subjects underwent a cardiac MRI (3T) exam including 4D-flow MRI of the aorta.Aortic curvature, arch shape, ascending aortic angle, ascending aortic diameter, and the stroke volume normalized by the aortic volume (nSV) were measured. Velocity, vorticity, and helicity were quantified across the thoracic aorta.Univariate and multivariate regressions were used to quantify continuous relationships between variables.Aortic diameter, ascending aortic angle, shape, and curvature all increased across age while nSV decreased (all P 0.0001). Systolic vorticity in the mid arch decreased by 50% across the age range (P 0.0001), while peak helicity decreased by 80% (P 0.0001). Curvature tightly governs optimal flow in the youngest quartile, with an effect size 1.5 to 4 times larger than other parameters in the descending aorta, but had a minimal influence with advancing age. In the upper quartile of age, flow dynamics were almost completely determined by nSV, exerting an effect size on velocity and vorticity10 times that of diameter and other shape factors.Aortic shape influences flow dynamics in younger subjects. Flow conditions become increasingly disturbed with advancing age, and in these conditions nSV has a more dominant effect on flow patterns than shape factors.3 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:90-100.

Peripheral veno-arterial extra corporeal membrane oxygenation (VA-ECMO) is an established technique for short-to-medium support of patients with severe cardiac failure. However, in patients with concomitant respiratory failure, the residual native circulation will provide deoxygenated blood to the upper body, and may cause differential hypoxemia of the heart and brain. In this paper, we present a general computational framework for the identification of differential hypoxemia risk in VA-ECMO patients. A range of different VA-ECMO patient scenarios for a patient-specific geometry and vascular resistance were simulated using transient computational fluid dynamics simulations, representing a clinically relevant range of values of stroke volume and ECMO flow. For this patient, regardless of ECMO flow rate, left ventricular stroke volumes greater than 28 mL resulted in all aortic arch branch vessels being perfused by poorly-oxygenated systemic blood sourced from the lungs. The brachiocephalic artery perfusion was almost entirely derived from blood from the left ventricle in all scenarios except for those with stroke volumes less than 5 mL. Our model therefore predicted a strong risk of differential hypoxemia in nearly all situations with some residual cardiac function for this combination of patient geometry and vascular resistance. This simulation highlights the potential value of modelling for optimising ECMO design and procedures, and for the practical utility for personalised approaches in the clinical use of ECMO.

Purpose To show that the use of a multi-velocity encoding (VENC) 4D-flow approach offers significant improvements in the characterization of complex flow in the aorta. Four-dimensional flow magnetic resonance imaging (MRI) (4D-flow) can be used to measure complex flow patterns and dynamics in the heart and major vessels. The quality of the information derived from these measures is dependent on the accuracy of the vector field, which is limited by the vector-to-noise ratio. Materials and Methods A 4D-flow protocol involving three different VENC values of 150, 60, and 20 cm/s was performed on six control subjects and nine patients with type-B chronic aortic dissection at 3T MRI. Data were processed using a single VENC value (150 cm/s) or using a fused dataset that selected the lowest appropriate VENC for each voxel. Performance was analyzed by measuring spatial vector angular correlation, magnitude correlation, temporal vector conservation, and “real-world” streamline tracing performance. Results The multi-VENC approach provided a 31% improvement in spatial and 53% improvement in temporal precision of velocity vector measurements during the mid-late diastolic period, where 99% of the flow vectors in the normal aorta are below 20 cm/s. In low-flow conditions this resulted in practical improvements of greater than 50% in pathline tracking and streamline tracing quantified by streamline curvature measurements. Conclusion A multi-VENC 4D-flow approach provides accurate vector data across normal physiological velocities observed in the aorta, dramatically improving outputs such as pathline tracking, streamline estimation, and further advanced analyses.J. Magn. Reson. Imaging 2015.

Background:\ud Femoroacetabular impingement syndrome (FAI), a hip disorder affecting active young adults, is believed to be a leading cause of hip osteoarthritis (OA). Current management approaches for FAI include arthroscopic hip surgery and physiotherapy-led non-surgical care; however, there is a paucity of clinical trial evidence comparing these approaches. In particular, it is unknown whether these management approaches modify the future risk of developing hip OA. The primary objective of this randomised controlled trial is to determine if participants with FAI who undergo hip arthroscopy have greater improvements in hip cartilage health, as demonstrated by changes in delayed gadolinium-enhanced magnetic resonance imaging (MRI) of cartilage (dGEMRIC) index between baseline and 12 months, compared to those who undergo physiotherapy-led non-surgical management.\ud \ud Methods:\ud This is a pragmatic, multi-centre, two-arm superiority randomised controlled trial comparing hip arthroscopy to physiotherapy-led management for FAI. A total of 140 participants with FAI will be recruited from the clinics of participating orthopaedic surgeons, and randomly allocated to receive either surgery or physiotherapy-led non-surgical care. The surgical intervention involves arthroscopic FAI surgery from one of eight orthopaedic surgeons specialising in this field, located in three different Australian cities. The physiotherapy-led non-surgical management is an individualised physiotherapy program, named Personalised Hip Therapy (PHT), developed by a panel to represent the best non-operative care for FAI. It entails at least six individual physiotherapy sessions over 12 weeks, and up to ten sessions over six months, provided by experienced musculoskeletal physiotherapists trained to deliver the PHT program. The primary outcome measure is the change in dGEMRIC score of a ROI containing both acetabular and femoral head cartilages at the chondrolabral transitional zone of the mid-sagittal plane between baseline and 12 months. Secondary outcomes include patient-reported outcomes and several structural and biomechanical measures relevant to the pathogenesis of FAI and development of hip OA. Interventions will be compared by intention-to-treat analysis.\ud \ud Discussion:\ud The findings will help determine whether hip arthroscopy or an individualised physiotherapy program is superior for the management of FAI, including for the prevention of hip OA.\ud \ud Trial registration:\ud Australia New Zealand Clinical Trials Registry reference: ACTRN12615001177549. Trial registered 2/11/2015 (retrospectively registered).

Background: Chronic descending thoracic aortic dissection (CDTAD) following surgical repair of ascending aortic dissection requires long-term imaging surveillance. We investigated four-dimensional (4D)-flow magnetic resonance imaging (MRI) with a novel multi-velocity encoding (multi-VENC) technique as an emerging clinical method enabling the dynamic quantification of blood volume and velocity throughout the cardiac cycle. Methods: Patients with CDTAD (n = 10; mean age, 55.1 years; standard deviation (SD) 10.8) and healthy volunteers (n = 9; mean age, 37.1 years; SD 11.4; p < 0.01) underwent 3T MRI, and standard views and 4D-flow data were obtained. Flow measurements were made in selected regions of interest within the ascending and descending thoracic aorta. Results: The overall flow profile at peak systole was reduced in the false lumen (FL) compared with the true lumen (TL) and normal aortas (p < 0.05 for velocity < 0.4 m/s). Peak systolic flow rate per aortic lumen area (mL/s/cm2) was lower in the FL than in the TL (p < 0.05), and both rates were lower than that of control aortas (p < 0.05). Blood flow reversal was higher in the FL than in the TL throughout the descending aorta in CDTAD patients (p < 0.05). A derived pulsatility index was elevated in the TL compared with that in the FL in CDTAD patients. Generated pathline images demonstrated flow patterns in detail, including sites of communication between the true and FL. Conclusions: 4D-flow MRI revealed FL blood flow and reduced blood flow velocity and flow rate in the TL of CDTAD patients compared with normal aortas of healthy participants. Thus, multi-VENC 4D-flow MRI could serve as an adjunct in the long-term assessment of CDTAD following surgical repair of ascending aortic dissection.

Background Diastolic dysfunction is a major cause of morbidity in obese individuals. We aimed to assess the ability of magnetic resonance imaging (MRI) derived left atrial (LA) strain to detect early diastolic dysfunction in individuals with obesity and type 2 diabetes, and to explore the association between cardiac adipose tissue and LA function. Methods Twenty patients with obesity and T2D (55 ± 8 years) and nineteen healthy controls (48 ± 13 years) were imaged using cine steady state free precession and 2-point Dixon cardiovascular magnetic resonance. LA function was quantified using a feature tracking technique with definition of phasic longitudinal strain and strain rates, as well as radial motion fraction and radial velocities. Results Systolic left ventricular size and function were similar between the obesity and type 2 diabetes and control groups by MRI. All patients except four had normal diastolic assessment by echocardiography. In contrast, measures of LA function using magnetic resonance feature tracking were uniformly altered in the obesity and type 2 diabetes group only. Although there was no significant difference in intra-myocardial fat fraction, Dixon 3D epicardial fat volume(EFV) was significantly elevated in the obesity and type 2 diabetes versus control group (135 ± 31 vs. 90 ± 30 mL/m2, p Conclusions LA MRI-strain may be a sensitive tool for the detection of early diastolic dysfunction in individuals with obesity and type 2 diabetes and correlated with BMI and epicardial fat supporting a possible association between adiposity and LA strain. Trials Registration Australian New Zealand Clinical Trials Registry No. ACTRN12613001069741

4D-flow MRI obtains a time-dependent 3D velocity field; however, its use for the calculation of higher-order parameters is limited by noise. We present an algorithm for denoising 4D-flow data.By integrating a velocity field and eliminating streamlines in noisy flow, depicted by high curvature, a denoised dataset may be extracted. This method, defined as the velocity field improvement (VFIT) algorithm, was validated in an analytical dataset and using in vivo data in comparison with a computation fluid dynamics (CFD) simulation. As a proof of principal, wall shear stress (WSS) measurements in the descending aorta were compared with those defined by CFD.The VFIT algorithm achieved a100% noise reduction of a corrupted analytical dataset. In addition, 4D-flow data were cleaned to show improved spatial resolution and near wall velocity representation. WSS measures compared well with CFD data and bulk flow dynamics were retained (2% difference in flow measurements).This study presents a method for denoising 4D-flow datasets with improved spatial resolution. Bulk flow dynamics are accurately conserved while velocity and velocity gradient fields are improved; this is important in the calculation of higher-order parameters such as WSS, which are shown to be more comparable to CFD measures. Magn Reson Med 78:1959-1968, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

To quantitatively characterize the central role of vortex formation on the flow patterns and energy transfer within the right atrium (RA).4D-flow magnetic resonance imaging (MRI) data with multiple encoding velocities was acquired in 12 healthy subjects at 3T. Particles entering the RA were classified according to the origin of entry. Vortex membership was numerically derived by assessing the location of pathline center of curvature relative to the vortex core, defined by Q-criteria. Flow dynamics and energetics were assessed using paired t-tests.The majority of flow (74%) passes through the RA in a single beat, with a very small volume fraction retained longer than two beats (1%). RA flow was dominated by a governing vortex, comprising 79% of total flow, and acting to preserve kinetic energy. Flow comprising the vortex enters the RA significantly earlier than nonvortex flow (P0.01). The majority of nonvortex flow enters the RA during systole, traversing the RA via a direct path with a significantly shorter residence time and distance traveled (both P0.01).Blood flow momentum is preserved during systole within a dominant vortex, which we are able to characterize numerically using a semiautomated approach. Our analytical approach has potential for application to understanding right heart function in health and disease.1 J. Magn. Reson. Imaging 2017;45:1046-1054.

Spontaneous dissection of the cervical internal carotid artery (sICAD) is a major cause of stroke in young adults. A tear in the inner part of the vessel wall triggers sICAD as it allows the blood to enter the wall and develop a transmural hematoma. The etiology of the tear is unknown but many patients with sICAD report an initiating trivial trauma. We thus hypothesised that the site of the tear might correspond with the location of maximal stress in the carotid wall. Carotid artery geometries segmented from magnetic resonance images of a healthy subject at different static head positions were used to define a path of motion and deformation of the right cervical internal carotid artery (ICA). Maximum head rotation to the left and rotation to the left combined with hyperextension of the neck were investigated using a structural finite element model. A role of the carotid sinus as a geometrically compliant feature accommodating extension of the artery is shown. At the extreme range of the movements, the geometrical compliance of the carotid sinus is limited and significant stress concentrations appear just distal to the sinus with peak stresses at the internal wall on the posterior side of the vessel following maximum head rotation and on the anteromedial portion of the vessel wall following rotation and hyperextension. Clinically, the location of sICAD initiation is 10-30 mm distal to the origin of the cervical ICA, which corresponds with the peak stress locations observed in the model, thus supporting trivial trauma from natural head movements as a possible initiating factor in sICAD.

Cardiac magnetic resonance (CMR) has the potential to provide early detection of cardiac involvement in Fabry disease. We aimed to gain further insight into this by assessing a cohort of Fabry patients using CMR.Fifty genotype-positive Fabry subjects (age 45±2 years; 50% male) referred for CMR and 39 matched controls (age 40±2 years; 59% male) were recruited. Patients had a mean Mainz severity score index of 15±2 (range 0-46), reflecting an overall mild degree of disease severity. Compared with controls, Fabry subjects had a 34% greater left ventricular mass (LVM) index (82±5 vs 61±2 g/m(2), p=0.001) and had a significantly greater papillary muscle contribution to total LVM (13±1 vs 6±0.5%, p0.001), even in the absence of left ventricular hypertrophy (LVH). Late gadolinium enhancement (LGE) was present in 15 Fabry subjects (9/21 males and 6/23 females). The most common site for LGE was the basal inferolateral wall (93%, 14/15). There was a positive association between LVM index and LGE. Despite this, there were two males and three females with no LVH that displayed LGE. Of Fabry subjects who were not on enzyme replacement therapy at enrolment (n=28), six were reclassified as having cardiac involvement (four LVH-negative/LGE-positive, one LVH-positive/LGE-positive and one LVH-positive/LGE-negative).CMR was able to detect cardiac involvement in 48% of this Fabry cohort, despite the overall mild disease phenotype of the cohort. Of those not on ERT, 21% were reclassified as having cardiac involvement allowing improved risk stratification and targeting of therapy.

Sphingolipid deposition in Fabry disease causes left ventricular (LV) hypertrophy, of which the accurate assessment is essential. Cardiovascular magnetic resonance (CMR) has been proposed as the gold standard. However, there is debate in the literature as to whether papillary muscles and trabeculations (P&T) should be included in LV mass (LVM). We examined the accuracy of 2 CMR methods of assessing LVM and LV volumes, including (M inc P&T) or excluding (M ex P&T) P&T, in a cohort of Fabry disease subjects (n = 20) compared to a matched control group (n = 20). Significant differences between the two measurement methods were observed for LV end-diastolic volume, LV end-systolic volume, LVM, and LV ejection fraction (LVEF) in both groups. These differences were significantly greater in the Fabry group compared to controls, except for LVEF. P&T contributed to a greater percentage of LVM in Fabry subjects than controls (20 ± 1% vs 13 ± 2%, p = 0.01). In the control group, both volume-derived methods (M inc P&T or MexP&T) provided accurate SV measurements compared with the internal reference of velocity-encoded aortic flow. In the Fabry group, inclusion of P&T (M inc P&T) resulted in good concordance with phase contrast flow imaging (difference between flow and volume techniques: 1 ± 3 ml, p = 0.7). The volumetric contribution of P&T in Fabry disease is markedly increased relative to healthy controls. Failure to account for this results in significant underestimation of LVM and results in misclassification of a proportion of subjects.

To show that the use of a multi-velocity encoding (VENC) 4D-flow approach offers significant improvements in the characterization of complex flow in the aorta. Four-dimensional flow magnetic resonance imaging (MRI) (4D-flow) can be used to measure complex flow patterns and dynamics in the heart and major vessels. The quality of the information derived from these measures is dependent on the accuracy of the vector field, which is limited by the vector-to-noise ratio.A 4D-flow protocol involving three different VENC values of 150, 60, and 20 cm/s was performed on six control subjects and nine patients with type-B chronic aortic dissection at 3T MRI. Data were processed using a single VENC value (150 cm/s) or using a fused dataset that selected the lowest appropriate VENC for each voxel. Performance was analyzed by measuring spatial vector angular correlation, magnitude correlation, temporal vector conservation, and "real-world" streamline tracing performance.The multi-VENC approach provided a 31% improvement in spatial and 53% improvement in temporal precision of velocity vector measurements during the mid-late diastolic period, where 99% of the flow vectors in the normal aorta are below 20 cm/s. In low-flow conditions this resulted in practical improvements of greater than 50% in pathline tracking and streamline tracing quantified by streamline curvature measurements.A multi-VENC 4D-flow approach provides accurate vector data across normal physiological velocities observed in the aorta, dramatically improving outputs such as pathline tracking, streamline estimation, and further advanced analyses.

Sydney Translational Imaging Laboratory, Sydney Medical School and Charles Perkins Centre, University of Sydney, Sydney, NSW, Australia Department of Cardiology, Royal North Shore Hospital, Sydney, NSW, Australia Heart Research Institute, Sydney, NSW, Australia North Shore Heart Research Group, Kolling Institute, University of Sydney, Sydney, NSW, Australia Department of Radiology, Royal Prince Alfred Hospital, Sydney, NSW, Australia

Background Quantification of myocardial “area at risk” ( AAR ) and myocardial infarction ( MI ) zone is critical for assessing novel therapies targeting myocardial ischemia–reperfusion ( IR ) injury. Current “gold‐standard” methods perfuse the heart with Evan's Blue and stain with triphenyl tetrazolium chloride ( TTC ), requiring manual slicing and analysis. We aimed to develop and validate a high‐resolution 3‐dimensional (3D) magnetic resonance imaging (MRI) method for quantifying MI and AAR . Methods and Results Forty‐eight hours after IR was induced, rats were anesthetized and gadopentetate dimeglumine was administered intravenously. After 10 minutes, the coronary artery was re‐ligated and a solution containing iron oxide microparticles and Evan's Blue was infused (for comparison). Hearts were harvested and transversally sectioned for TTC staining. Ex vivo MR images of slices were acquired on a 9.4‐T magnet. T2* data allowed visualization of AAR , with microparticle‐associated signal loss in perfused regions. T1 data demonstrated gadolinium retention in infarcted zones. Close correlation ( r =0.92 to 0.94; P MRI and Evan's Blue/ TTC measures for both AAR and MI was observed when the combined techniques were applied to the same heart slice. However, 3D MRI acquisition and analysis of whole heart reduced intra‐observer variability compared to assessment of isolated slices, and allowed automated segmentation and analysis, thus reducing interobserver variation. Anatomical resolution of 81 μm 3 was achieved (versus ≈2 mm with manual slicing). Conclusions This novel, yet simple, MRI technique allows precise assessment of infarct and AAR zones. It removes the need for tissue slicing and provides opportunity for 3D digital analysis at high anatomical resolution in a streamlined manner accessible for all laboratories already performing IR experiments.

Thoracic aortic aneurysm (TAA) is reported with an occurrence of 4.5–5.9/100,000 persons per year (Davis et al. 2014). Physiopathology of TAA includes modification of tissue influenced by flow modi...

Spontaneous internal carotid artery (ICA) dissection (sICAD) results from an intimal tear located around the distal carotid sinus. The mechanisms causing the tear are unknown. This case-control study tested the hypotheses that head movements increase the wall stress in the cervical ICA and that the stress increase is greater in patients with sICAD than in controls. Five patients with unilateral, recanalized, left sICAD and five matched controls were investigated before and after maximal head rotation to the left and neck hyperextension after 45° head rotation to the left. The anatomy of the extracranial carotid arteries was assessed by magnetic resonance imaging and used to create finite element models of the right ICA. Wall stress increased after head movements. Increases above the 80th and 90th percentile were located at the intimal side of the artery wall from 7.4 mm below to 10 mm above the cranial edge of the carotid sinus, i.e., at the same location as histologically confirmed tears in patients with sICAD. Wall stress increase did not differ between patients and controls. The present findings suggest that wall stress increases at the intimal side of the artery wall surrounding the distal edge of the carotid bulb after head movements may be important for the development of carotid dissection. The lack of wall stress difference between the two groups indicates that the carotid arteries of patients with carotid dissection have either distinct functional or anatomical properties or endured unusually heavy wall stresses to initiate dissection.

[1] Drag forces on macrophytes in a steady turbulent flow consist of both a mean and fluctuating component. Macrophytes that form a canopy experience lower mean forces due to a reduction of velocities within the canopy. However, submerged canopies also generate additional turbulence. In this study, an experiment is conducted in a laboratory flume to investigate how canopy density influences both mean and unsteady forces on a macrophyte. Canopies with densities of 39, 156, and 625 stems m−2 are constructed from 25 cm lengths of Lagarosiphon major. Drag is measured on a single stem within the canopy at four flow rates. The results show that although mean forces are reduced with increasing canopy density, the unsteady force (characterized by RMS of fluctuations from the mean) increases with the square-root of canopy density. The force response of the stem to the turbulence was frequency dependent with the strongest response at low frequencies.

This paper describes a device, the submersible drag gauge (SDG), that can be used for drag measurements in studies of flow-biota interactions at low (setup A) and high (setup B) load applications. The device is designed so that solely drag forces acting on a test object in a boundary layer flow are measured. The SDG can measure drag on organism(s), such as macrophtyes, crayfish or mussels, as well as a combination of such organisms and sediments assembled in a variety of arrangements in both laboratory and field conditions. Laboratory calibrations over the range of 0 to 4 showed that setup A registered forces as low as 0.02 N, whereas setup B often did not register forces up to c. 0.15 N. The relative standard error of drag measurements was 0.2 (setup A) or 1 (setup B). Using a rigid cylinder, and natural and artificial (plastic) Egeria densa as examples, showed how the SDG can serve in studies of flow-biota interactions such as drag-velocity relations, assessments of drag coefficients, or the frequency spectrum of macrophyte drag., Effets du canal expérimental sur les mesures de traînée sur des macrophytes flexibles et un cylindre rigide.

This paper describes a device, the submersible drag gauge (SDG), that can be used for drag measurements in studies of flow-biota interactions at low (setup A) and high (setup B) load applications. The device is designed so that solely drag forces acting on a test object in a boundary layer flow are measured. The SDG can measure drag on organism(s), such as macrophtyes, crayfish or mussels, as well as a combination of such organisms and sediments assembled in a variety of arrangements in both laboratory and field conditions. Laboratory calibrations over the range of 0 to 4 showed that setup A registered forces as low as 0.02 N, whereas setup B often did not register forces up to c. 0.15 N. The relative standard error of drag measurements was 0.2 (setup A) or 1 (setup B). Using a rigid cylinder, and natural and artificial (plastic) Egeria densa as examples, showed how the SDG can serve in studies of flow-biota interactions such as drag-velocity relations, assessments of drag coefficients, or the frequency spectrum of macrophyte drag., Une balance de traînée submersible pour mesurer les forces subies par les plantes aquatiques et autres organismes.