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.

Purpose To compare pulmonary artery flow using Cartesian and radially sampled four-dimensional flow sensitive (4D flow) magnetic resonance imaging at two institutions. Methods 19 healthy and 17 pulmonary arterial hypertension (PAH) subjects underwent a Cartesian 4D flow acquisition (institution 1) or a three-dimensional radial acquisition (institution 2). The diameter, peak systolic velocity (Vmax), peak flow (Qmax), stroke volume (SV), and wall shear stress (WSS) were computed in two-dimensional analysis planes at the main, right, and left pulmonary artery. Inter-observer variability, inter-institutional differences, flow continuity, and the hemodynamic measurements in healthy and PAH subjects were assessed. Results Vmax, Qmax, SV, and WSS at all locations were significantly lower (p<0.05) in PAH compared to healthy subjects. The limits of agreement were 0.16 m/s, 2.4 L/min, 10 mL, and 0.31 N/m2 for Vmax, Qmax, SV, and WSS, respectively. Differences between Qmax, and SV using Cartesian and radial sequences were not significant. Plane placement and acquisition exhibited isolated, site-based differences between Vmax and WSS. Conclusions 4D flow MRI was used to detect differences in pulmonary artery hemodynamics for PAH subjects. Flow and WSS in healthy and PAH subject cohorts were similar between Cartesian- and radial-based 4D flow MRI acquisitions with minimal inter-observer variability.

Objective Ventricular kinetic energy measurements may provide a novel imaging biomarker of declining ventricular efficiency in patients with repaired Tetralogy of Fallot (rTOF). Our purpose was to assess differences in ventricular kinetic energy (KE) with four-dimensional (4D) Flow MRI between patients with rTOF and healthy volunteers. Methods Cardiac MR (CMR), including 4D Flow MRI, was performed at rest in 10 subjects with rTOF and nine healthy volunteers using clinical 1.5T and 3T MRI scanners. Right and left ventricular kinetic energy (KERV and KELV), main pulmonary artery flow (QMPA), and aortic flow (QAO) were quantified using 4D Flow MRI data. Right and left ventricular size and function were measured using standard CMR techniques. Differences in peak systolic KERV and KELV in addition to the QMPA/KERV and QAO/KELV ratios between groups were assessed. KE indices were compared to conventional CMR parameters. Results Peak systolic KERV and KELV were higher in rTOF subjects (6.06±2.27mJ and 3.55±2.12mJ, respectively) than healthy volunteers (5.47±2.52mJ and 2.48±0.75mJ, respectively) but not statistically significant (p= .65 and p= .47, respectively). The QMPA/KERV and QAO/KELV ratios were lower in rTOF subjects (7.53±5.37mL/(cycle-mJ) and 9.65±6.61mL/(cycle-mJ), respectively) than healthy volunteers (19.33±18.52mL/(cycle-mJ) and 35.98±7.66mL/(cycle-mJ), respectively; p< .05). QMPA/KERV and QAO/KELV were weakly correlated to ventricular size and function. Conclusions Greater ventricular KE is necessary to generate flow in the pulmonary and aortic circulations in rTOF. Quantification of ventricular KE in patients with rTOF is a new observation. Future studies are needed to determine if changes in ventricular KE can provide earlier evidence of ventricular dysfunction and guide future medical and surgical interventions.

Purpose 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. Methods & Materials 24 cirrhotic patients (55.9±10.4years) were scanned using 5-point PC-VIPR for high spatial resolution imaging with large volume coverage at 3T using a 32-channel body coil. Vessel segmentation and hemodynamic visualization included color-coded 3D streamlines and particle traces. Segmentation quality was compared to contrast-enhanced multi-phase liver imaging. Flow pattern analysis was performed in consensus of 3 readers. The MELD score was calculated to estimate disease severity and was correlated to image quality. Results Good to excellent visualization quality was achieved in 23/24 cases. All arterial vessels and 144/168 vessels of the portal venous (PV) circulation were unambiguously identified. No correlation with the MELD score was found. 8/148 vessels of the PV circulation demonstrated reverse (hepatofugal) flow. Hepatofugal flow small tributaries to PV flow were present in three cases despite hepatopetal flow in the PV. Conclusion This feasibility study demonstrates the feasibility of PC-VIPR for simultaneous morphological and hemodynamic assessment of the hepatic and splanchnic vasculature in cirrhosis and portal hypertension. Future studies with quantitative analyses are warranted.

Purpose Portal and mesenteric hemodynamics is greatly altered in portal hypertension patients. This study utilizes four-dimensional flow MRI to visualize and quantify changes in abdominal hemodynamics in patients with portal hypertension undergoing meal challenge. Methods & Materials Twelve portal hypertension patients and six healthy subjects participated in the study. Baseline MRI was acquired after 5 hours of fasting. Post-meal MRI was obtained 20 minutes after subjects ingested EnSurePlus®(574mL). Imaging was performed at 3T using 4D flow MRI with an undersampled radial acquisition. Flow measurements were performed blinded to subject status (fasting/meal). Flow values for each vessel were compared before and after the meal challenge using paired Student t-tests (P<0.05). Results After meal challenge, significant increases in blood flow were observed in supra-celiac aorta, portal vein, superior mesenteric vein and artery, in both groups (p<0.05). In patients, hepatic artery (p=0.001) and splenic vein (p=0.045) flow decreased while azygos vein flow (p=0.002) increased. Conclusion Portal venous flow regulation to adjust the increasing mesenteric venous flow after a meal challenge may be impaired in patients with cirrhosis. The ability to comprehensively quantify the hemodynamic response of the abdominal vasculature to a meal challenge using 4D flow MRI reveals the potential of this technique to noninvasively characterize portal hypertension hemodynamics.