Purpose to implement and validate in vivo radial 4D flow MRI for quantification of blood flow in the hepatic arterial, portal venous and splanchnic vasculature of healthy volunteers and patients with portal hypertension. Methods & Materials 17 patients with portal hypertension and 7 subjects with no liver disease were included in this HIPAA-compliant and IRB-approved study. Exams were conducted at 3T using a 32-channel body coil with large volumetric coverage and 1.4mm isotropic true spatial resolution. Using post-processing software, cut-planes orthogonal to vessels were used to quantify flow (L/min) in the hepatic and splanchnic vasculature. Results Flow quantification was successful in all cases. Portal vein and supra-celiac aorta flow demonstrated high variability among patients. Measurements were validated indirectly using internal consistency at three different locations within the portal vein (error=4.2±3.9%) and conservation of mass at the portal confluence (error=5.9±2.5%) and portal bifurcation (error=5.8±3.1%). Discussion This work demonstrates the feasibility of radial 4D flow MRI to quantify flow in the hepatic and splanchnic vasculature. Flow results agreed well with data reported in the literature, and conservation of mass provided indirect validation of flow quantification. Flow in patients with portal hypertensions demonstrated high variability with patterns and magnitude consistent with the hyperdynamic state that commonly occurs in portal hypertension.

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.

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Introduction Low wall shear stress (WSS) values are frequently observed in arterial regions that are prone to atherosclerotic plaque formation and have also been implicated in the pathogenesis of saccular cerebral aneurysms. Acquisition of WSS values in-vivo has been challenging, especially using non-invasive techniques and within clinically-useful imaging times. We have recently implemented radial phase-contrast techniques that allow high resolution angiograms with velocity information to be acquired within clinically-useful imaging times. Methods 10 healthy volunteers were scanned using PC-VIPR and PC-SOS, two high resolution phase-contrast techniques at spatial resolutions of 0.67×0.67×0.67mm3 and 0.4×0.4×1mm3 respectively. Velocity data from the two acquisitions was imported into a custom Matlab runtime environment that automatically calculated WSS values using Green’s Theorem and B-spline interpolation. Results Time average axial WSS was 1.069 N/m2 (95% confidence interval: 0.8628 < x < 1.276) in the left and right middle cerebral arteries of the 10 healthy volunteers (n=20) when scanned by PC-VIPR, and 1.670 N/m2 when scanned by PC-SOS (95% confidence interval: 1.395 < x < 1.946). This difference in means was statistically significant (p < 0.002). Discussion Previous investigators have found that higher spatial resolution results in higher WSS measurements because smaller voxel size results in fewer partial volume effects. This was true in our study as well. In this study, we found that PC-SOS has significantly higher spatial resolution than PC-VIPR and this followed in the WSS measurements. Conclusion Higher in-plane spatial resolution allows WSS calculations to be performed more accurately because of increased precision near the vessel boundary.