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 Fisher's 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 PA's. 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.
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 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.
Objectives To validate radially undersampled 5-point velocity-encoded time-resolved flow-sensitive MRI (“PC-VIPR”) for quantification of ascending aortic (AAO) and main pulmonary artery (MPA) flow in-vivo Materials and Methods Data from 18 healthy volunteers (41.6±16.2years (22–73); BMI 26.0±3.5 (19.1–31.4) scanned at 3T with a 32-channel-coil were included. Left and right ventricular stroke volumes (LVSV and RVSV, respectively) calculated from contiguous short-axis CINE-bSSFP slices were used as the primary reference for cardiac output. Flow measured from 2D-PC-MRI in the AAO and MPA served as a secondary reference. Time-resolved 3-dimensional flow-sensitive MRI (4D-Flow-MRI) using PC-VIPR was performed with a velocity sensitivity Venc=150cm/s reconstructed to 20 time frames at 1.4mm isotropic spatial resolution. In 11/20 subjects, phantom corrected 4D-Flow-MRI data was also assessed. Differences between methods of calculating LV and RV cardiac output were assessed with Bland-Altman analysis (BA, average difference ± 2SD). The QP/QS-ratio was calculated for each method. Results Initially, PCVIPR compared unfavorably to CINE-bSSFP (LVSV: 96.5±14.4ml, RVSV: 93.6±14.0mL vs. 81.2±24.3mL (AAO) and 85.6±25.4mL (MPA); p=0.027 and 0.25) with BA differences of −14.6±44.0mL (AAO) and −9.0±45.9mL (MPA). While phantom correction had minor effects on 2D-PC-MRI results and comparison to CINE-bSSFP, it improved PC-VIPR results: BA differences between CINE-bSSFP and PC-VIPR after correction were −1.4±15.3ml (AAO) and −4.1±16.1mL (MPA); BA comparison with 2D-PC-MRI improved to −12.0±48.1mL (AAO) and −2.2±19.5mL (MPA). QP/QS-ratio results for all techniques were within physiologic limits. Conclusions Accurate quantification of AAO and MPA flows with radially undersampled 4D-Flow-MRI applying 5-point velocity encoding is achievable when phantom correction is used.
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