This study used magnetic resonance imaging (MRI), computational fluid dynamics (CFD) modeling, and in vitro experiments to predict patient-specific alterations in hepatic hemodynamics in response to partial hepatectomy in living liver donors. 4D Flow MRI was performed on three donors before and after hepatectomy and models of the portal venous system were created. Virtual surgery was performed to simulate (1) surgical resection and (2) post-surgery vessel dilation. CFD simulations were conducted using in vivo flow data for boundary conditions. CFD results showed good agreement with in vivo data, and in vitro experimental values agreed well with imaging and simulation results. The post-surgery models predicted an increase in all measured hemodynamic parameters, and the dilated virtual surgery model predicted post-surgery conditions better than the model that only simulated resection. The methods used in this study have potential significant value for the surgical planning process for the liver and other vascular territories.

Blood flow metrics obtained with four-dimensional (4D) flow phase contrast (PC) magnetic resonance imaging (MRI) can be of great value in clinical and experimental cerebrovascular analysis. However, limitations in both quantitative and qualitative analyses can result from errors inherent to PC MRI. One method that excels in creating low-error, physics-based, velocity fields is computational fluid dynamics (CFD). Augmentation of cerebral 4D flow MRI data with CFD-informed neural networks may provide a method to produce highly accurate physiological flow fields. In this preliminary study, the potential utility of such a method was demonstrated by using high resolution patient-specific CFD data to train a convolutional neural network, and then using the trained network to enhance MRI-derived velocity fields in cerebral blood vessel data sets. Through testing on simulated images, phantom data, and cerebrovascular 4D flow data from 20 patients, the trained network successfully de-noised flow images, decreased velocity error, and enhanced near-vessel-wall velocity quantification and visualization. Such image enhancement can improve experimental and clinical qualitative and quantitative cerebrovascular PC MRI analysis.

To further understand the relationship between cardiac function and flow, on the basis of sex, by quantifying cardiac flow characteristics and relating them to cardiac muscle performance in young adults. Materials and Methods:In this cross-sectional study, cardiac four-dimensional flow MRI and two-dimensional cine MRI were performed in 20 male and 19 female volunteers aged 20-35 years. Velocity-based metrics of flow, kinetic energy (KE), vorticity, and efficiency indexes were quantified, as well as cardiac strain metrics.Results: Peak systolic blood KE (men: 4.76 mJ ± 2.66 [standard deviation]; women: 3.36 mJ ± 1.43; P = .047) was significantly higher in the male left ventricle (LV) than in the female LV. Peak systolic vorticity index (men: 0.008 radian • m 2 /mL • sec ± 0.005; women: 0.014 radian • m 2 /mL • sec ± 0.007; P = .007), peak diastolic vorticity index (men: 0.007 radian • m 2 /mL • sec ± 0.006; women: 0.014 radian • m 2 /mL • sec ± 0.010; P = .015), and cycle-average vorticity (men: 0.006 radian/sec ± 0.001; women: 0.011 radian/sec ± 0.002; P = .001) were significantly higher in the LV of women than they were in the LV of men. Radial, circumferential, and long-axis strain metrics were significantly higher in the female LV than in the male LV (P < .05). Circumferential systolic and diastolic strain rates displayed moderate correlation to peak systolic (r = −0.38; P = .022) and diastolic vorticity (r = 0.40; P = .015) values, respectively. Results are reported as mean ± standard deviation. Conclusion:LV vorticity metrics were observed to be higher in women than in men and displayed moderate correlation to cardiac strain metrics. The methods and results of this study may be used to further understand the sex-based cardiac efficiency relationship between cardiac function and flow.

Background Characterizing the flow of the Fontan circuit, and correlating flow characteristics with the development of complications, is an important clinical challenge. Past work has analyzed the flow characteristics of Fontan circulation on a component‐by‐component basis. 4D flow MRI with radial projections allows for large volumetric coverage, and therefore can be used to analyze the flow through many codependent cardiovascular components in a single imaging session. Purpose To describe flow characteristics across the entire Fontan circuit and to compare these with the flow characteristics in healthy volunteers. Study Type Prospective. Subjects Eleven single ventricle patients with a Fontan connection and 15 healthy controls. Sequence Phase contrast with vastly undersampled isotropic projection reconstruction (PC‐VIPR) at a field strength of 3 T. Assessment Cavopulmonary and ventricular flow distributions, blood flow kinetic energy, vorticities, efficiency indices, and other flow parameters were analyzed using Ensight and MatLab. Statistical Tests The results were compared across Fontan subjects, between respiratory phases, and between Fontan subjects and healthy volunteers using a Student's t‐test for unequal sample sizes and linear regression. Results Cava‐specific pulmonary flow distributions of Fontan patients varied significantly between respiratory phases (P < 0.05). Ventricular kinetic energy (KE) was significantly higher in Fontan patients than it was in healthy controls, leading to a lower cardiac efficiency metric in the Fontan group. A significant diastolic KE time‐shift was also observed in the Fontan patient group. Peak diastolic KE was significantly higher in the single ventricle of patients with right ventricle morphology than it was in left ventricle morphology patients. Data Conclusion Radial 4D flow MRI can be used for comprehensive analysis of single ventricle Fontan flow characteristics. Level of Evidence: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019.

Aneurysm rupture has been suggested to be related to aneurysm geometry, morphology, and complex flow activity, therefore understanding aneurysm-specific hemodynamics is crucial. 4D Flow MRI has shown to be a feasible tool for assessing hemodynamics in intracranial aneurysms with high spatial resolution. However, it requires averaging over multiple heartbeats and cannot account for cycle-to-cycle hemodynamics variations. This study aimed to assess cycle-to-cycle flow dynamics variations in a patient-specific intracranial aneurysm model using tomographic particle image velocimetry (tomo-PIV) at a high image rate under pulsatile flow conditions. Timeresolved and time-averaged velocity flow fields within the aneurysm sac and estimations of wall shear stress (WSS) were compared with those from 4D Flow MRI. A one-way ANOVA showed a significant difference between cardiac cycles (p-value < 0.0001); however, differences were not significant after PIV temporal and spatial resolution was matched to that of MRI (p-value 0.9727). This comparison showed the spatial resolution to be the main contributor to assess cycle-to-cycle variability. Furthermore, the comparison with 4D Flow MRI between velocity components, streamlines, and estimated WSS showed good qualitative and quantitative agreement. This study showed the feasibility of patient-specific in-vitro experiments using tomo-PIV to assess 4D Flow MRI with high repeatability in the measurements.