Fraser M. Callaghan

Use of multi-velocity encoding 4D flow MRI to improve quantification of flow patterns in the aorta.

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.

Wall stress of the cervical carotid artery in patients with carotid dissection: a case-control study

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.

Cardiac involvement in genotype-positive Fabry disease patients assessed by cardiovascular MR

Objective 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. Methods/results 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/m2, p=0.001) and had a significantly greater papillary muscle contribution to total LVM (13±1 vs 6±0.5%, p<0.001), 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). Conclusions 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.

Quantifying right atrial filling and emptying: A 4D-flow MRI study

To quantitatively characterize the central role of vortex formation on the flow patterns and energy transfer within the right atrium (RA).

Flow mixing during peripheral veno-arterial extra corporeal membrane oxygenation – A simulation study

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.

Spatial resolution and velocity field improvement of 4D‐flow MRI

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.

Automated Quantification of Myocardial Salvage in a Rat Model of Ischemia-Reperfusion Injury Using 3D High-Resolution Magnetic Resonance Imaging (MRI)

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 Evans 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 Evans 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<0.05) of MRI and Evans 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 μm3 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.

4D flow magnetic resonance imaging: role in pediatric congenital heart disease:

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.

4D Multi-VENC Cardiac MRI: Characterisation of a Functional Stenosis of the Ascending Aorta.

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

Age-Related Changes of Shape and Flow Dynamics in Healthy Adult Aortas: A 4D Flow MRI Study: Age-Related Change of Shape and Flow Dynamics

Abnormal flow dynamics play an early and causative role in pathologic changes of the ascending aorta.