Benjamin R. Landgraf

4D cardiovascular magnetic resonance velocity mapping of alterations of right heart flow patterns and main pulmonary artery hemodynamics in tetralogy of Fallot

BackgroundTo assess changes in right heart flow and pulmonary artery hemodynamics in patients with repaired Tetralogy of Fallot (rTOF) we used whole heart, four dimensional (4D) velocity mapping (VM) cardiovascular magnetic resonance (CMR).MethodsCMR studies were performed in 11 subjects with rTOF (5M/6F; 20.1 ± 12.4 years) and 10 normal volunteers (6M/4F; 34.2 ± 13.4 years) on clinical 1.5T and 3.0T MR scanners. 4D VM-CMR was performed using PC VIPR (Phase Contrast Vastly undersampled Isotropic Projection Reconstruction). Interactive streamline and particle trace visualizations of the superior and inferior vena cava (IVC and SVC, respectively), right atrium (RA), right ventricle (RV), and pulmonary artery (PA) were generated and reviewed by three experienced readers. Main PA net flow, retrograde flow, peak flow, time-to-peak flow, peak acceleration, resistance index and mean wall shear stress were quantified. Differences in flow patterns between the two groups were tested using Fishers exact test. Differences in quantitative parameters were analyzed with the Kruskal-Wallis rank sum test.Results4D VM-CMR was successfully performed in all volunteers and subjects with TOF. Right heart flow patterns in rTOF subjects were characterized by (a) greater SVC/IVC flow during diastole than systole, (b) increased vortical flow patterns in the RA and in the RV during diastole, and (c) increased helical or vortical flow features in the PAs. Differences in main PA retrograde flow, resistance index, peak flow, time-to-peak flow, peak acceleration and mean wall shear stress were statistically significant.ConclusionsWhole heart 4D VM-CMR with PC VIPR enables detection of both normal and abnormal right heart flow patterns, which may allow for comprehensive studies to evaluate interdependencies of post-surgically altered geometries and hemodynamics.

In vivo three-dimensional MR wall shear stress estimation in ascending aortic dilatation

To estimate surface‐based wall shear stress (WSS) and evaluate flow patterns in ascending aortic dilatation (AscAD) using a high‐resolution, time‐resolved, three‐dimensional (3D), three‐directional velocity encoded, radially undersampled phase contrast MR sequence (4D PC‐MRI).

Noninvasive assessment of transstenotic pressure gradients in porcine renal artery stenoses by using vastly undersampled phase-contrast MR angiography.

PURPOSE To compare noninvasive transstenotic pressure gradient (TSPG) measurements derived from high-spatial- and temporal-resolution four-dimensional magnetic resonance (MR) flow measurements with invasive measurements obtained from endovascular pressure wires with digital subtraction angiographic guidance. MATERIALS AND METHODS After Animal Care and Use Committee approval, bilateral renal artery stenosis (RAS) was created surgically in 12 swine. Respiratory-gated phase-contrast vastly undersampled isotropic projection (VIPR) MR angiography of the renal arteries was performed with a 1.5-T clinical MR system (repetition time, 11.4 msec; echo time [first echo], 3.7 msec; 18,000 projection angles; imaging volume, 260 × 260 × 200 mm; acquired isotropic spatial resolution, 1.0 × 1.0 × 1.0 mm; velocity encoding, 150 cm/sec). Velocities measured with phase-contrast VIPR were used to calculate TSPGs by using Navier-Stokes equations. These were compared with endovascular pressure measurements (mean and peak) performed by using fluoroscopic guidance with regression analysis. RESULTS In 19 renal arteries with an average stenosis of 62% (range, 0%-87%), there was excellent correlation between the noninvasive TSPG measurement with phase-contrast VIPR and invasive TSPG measurement for mean TSPG (R² = 95.4%) and strong correlation between noninvasive TSPG and invasive TSPG for the peak TSPG measures (R² = 82.6%). The phase-contrast VIPR-derived TSPG measures were slightly lower than the endovascular measurements. In four arteries with severe stenoses and one occlusion (mean, 86%; range, 75%-100%), the residual lumen within the stenosis was too small to determine TSPG with phase-contrast VIPR. CONCLUSION The unenhanced MR angiographic technique with phase-contrast VIPR allows for accurate noninvasive assessment of hemodynamic significance in a porcine model of RAS with highly accurate TSPG measurements.

Velocity Measurements in the Middle Cerebral Arteries of Healthy Volunteers Using 3D Radial Phase-Contrast HYPRFlow: Comparison with Transcranial Doppler Sonography and 2D Phase-Contrast MR Imaging

BACKGROUND AND PURPOSE: We have developed PC HYPRFlow, a comprehensive MRA technique that includes a whole-brain CE dynamic series followed by PC velocity-encoding, yielding a time series of high-resolution morphologic angiograms with associated velocity information. In this study, we present velocity data acquired by using the PC component of PC HYPRFlow (PC-VIPR). MATERIALS AND METHODS: Ten healthy volunteers (6 women, 4 men) were scanned by using PC HYPRFlow and 2D-PC imaging, immediately followed by velocity measurements by using TCD. Velocity measurements were made in the M1 segments of the MCAs from the PC-VIPR, 2D-PC, and TCD examinations. RESULTS: PC-VIPR showed approximately 30% lower mean velocity compared with TCD, consistent with other comparisons of TCD with PC-MRA. The correlation with TCD was r = 0.793, and the correlation of PC-VIPR with 2D-PC was r = 0.723. CONCLUSIONS: PC-VIPR is a technique capable of acquiring high-resolution MRA of diagnostic quality with velocity data comparable with TCD and 2D-PC. The combination of velocity information and fast high-resolution whole-brain morphologic angiograms makes PC HYPRFlow an attractive alternative to current MRA methods.

Four‐dimensional velocity mapping of the hepatic and splanchnic vasculature with radial sampling at 3 tesla: A feasibility study in portal hypertension

To demonstrate the feasibility of PC‐VIPR (Phase Contrast Vastly undersampled Imaging with Projection Reconstruction) for the depiction and hemodynamic analysis of hepatic and splanchnic vessels in patients with portal hypertension.

Effect of temporal resolution on 4D flow MRI in the portal circulation

To demonstrate the use of temporal averaging with radial 4D flow magnetic resonance imaging (MRI) to reduce scan time for quantification and visualization of flow in the portal circulation. This study compared phase‐contrast MR angiography, 3D flow visualization, and flow quantification of portal venous hemodynamics of time‐averaged vs. time‐resolved reconstructions.

Rapid comprehensive evaluation of luminography and hemodynamic function with 3d radially undersampled phase contrast imaging MRI

Quantitative flow measurements with volumetric coverage and three directional flow encoding are technically feasible with magnetic resonance imaging yet prohibitively long in clinical settings. Data reconstruction from three dimensional angular undersampled MR acquisitions allows for dramatic reductions in scan time with tolerable imaging artifacts in many clinical applications. This approach provides high spatial resolution suitable for hemodynamic analysis in smaller vessels such as the renal artery, thereby providing additional crucial diagnostic information in a non invasive fashion. In an animal model, transstenotic pressure gradient measurements obtained with the novel acquisition scheme compared favorably with invasive intra arterial measurements (r = 3D 0.977; 95% CI: 0.931-0.998; p < 0.001). In addition, human studies demonstrate the suitability of the technique for lumen measurements as an alternative for contrast enhanced MR Angiography and the associated risks with the use of an external contrast agent in certain patient populations.

Analysis of right heart flow patterns in repaired Tetralogy of Fallot with 4D flow-sensitive MRI

Cardiac MRI (CMR) is used to follow patients after TOF repair to assess pulmonary regurgitation (PR), pulmonary stenosis (PS) and right ventricular (RV) function. 4D flow-sensitive MRI techniques enable visualization of complex flow patterns [1],[2]. With the ability to simultaneously acquire morphology and hemodynamics for visualization and quantification, they may improve evaluation of functional outcomes following surgery for complex CHD.

Whole chest MRA and velocimetry for congenital heart disease in less than 10 minutes with 3D radial phase contrast

Introduction MRI of congenital heart disease (CHD) usually requires acquisition of multiple anatomical and functional scans followed by several 2D phase contrast (PC) acquisitions in various scan planes for flow measurements. A 3D PC technique using vastly undersampled isotropic projection reconstruction (PCVIPR) with respiratory gating allows for volumetric 3D flow imaging with high spatial and temporal resolution over a large field of view in less than ten minutes during free breathing. Previously shown to be accurate for renal MRA and quanitification of pressure gradients, we have recently extended this technique to thoracic MRA (Figure 1).

Visualization and quantification of helical and vortical flow in ascending aortic aneurysms

Introduction Complex blood flow patterns in the ascending aorta have been associated with the pathophysiology of various cardiovascular diseases, including ascending aortic aneurysms (AscAA). Helical and turbulent flow in patients with aneurysms present an increased tangential force that could lead to further aortic dilation, dissection, or rupture. Characterization and quantification of these flow patterns could help predict disease progression.