Characterization of mesenteric and portal hemodynamics using 4D flow MRI: the effects of meals and diurnal variation

Abstract

Purpose: To determine the variability of blood flow measurements using 4D flow MRI in the portal and mesenteric circulations and to characterize the effects of meal ingestion, time of day, and between-day (diurnal) variations on portal and mesenteric hemodynamics.

Methods: In this IRB-approved and HIPAA-compliant study, 7 healthy and 7 portal hypertension patients imaged. MRI exams were conducted at 3 T using a 32-channel body coil with large volumetric coverage and 1.25-mm isotropic true spatial resolution. Blood flow was quantified (L/min) in the hepatic and splanchnic vasculature. The first MR scan was performed after at least 8 h of fasting. Subsequently, subjects ingested 574 mL EnSure Plus® orally. A second acquisition was started 20 min after the meal ingestion. A third scan was performed before lunch and a fourth acquisition took place 20 min after lunch. A fifth scan was performed around 4 pm. Finally, subjects returned one week later for a repeat morning visit, with identical conditions as the first visit.

Results: In healthy controls significant increase in blood flow was seen in the PV, SMV, SMA, HA, and SCAo in response to breakfast but only the SCAo, SMA, SMV, and PV had a significant response to lunch. In general, patients with cirrhosis showed reduced response to meals compared to that in healthy controls. Additionally, PV flow in patients had the highest value in the afternoon.

Conclusion: Effects of meal ingestion, time of day, and between-day variations were characterized using Radial 4D flow MRI in patients with cirrhosis and healthy controls.

Keywords: 4D flow MRI; Diurnal variation; Magnetic resonance imaging (MRI); Meal challenge; Phase contrast; Portal hypertension; Repeatability.

Figure 1:

Study schema, designed to determine the impact of meals and diurnal variation, as well as the repeatability (precision) of 4D flow MRI measurements in the portal and splanchnic circulation. Visit 1 occurred after eight or more hours of fasting, followed by Visit 2, 20 minutes after ingesting a standardized breakfast. Subjects were then imaged immediately before (Visit 3) and 20 minutes after (Visit 4) lunch at the cafeteria, and then again at 4pm (Visit 5). Finally, subjects returned a week later for a morning visit (Visit 6) under conditions identical to Visit 1.

Figure 2:

Location of cross-sectional planes for quantification of blood flow at the supraceliac aorta (SCAo), superior mesenteric artery (SMA), hepatic artery (HA), superior mesenteric vein (SMV), splenic vein (SV) and portal vein (PV).

Figure 3:

Portal blood flow increase in response to breakfast in a healthy volunteer. Pre breakfast (left) and Post breakfast (right). Velocity color-coded streamlines show increased velocities in the post case. White arrows show the direction of the flow revealing homogeneous flow in the pre-meal velocity field and unsteady vortical flow in the post-meal velocity field induced by the SMV flow increase.

Figure 4:

Velocity weighted phase contrast angiogram and superimposed corresponding flow velocity vectors. This patient has extensive gastroesophageal varices draining from the SV. This example demonstrates the large volumetric coverage and high spatial resolution achievable using radial 4D flow MRI. White arrows represent blood flow directionality.

Figure 5:

Volume rendered phase contrast angiogram with superimposed flow velocity streamlines inn a patient has large periumbilical collateral (PUC) and a splenorenal shunt (SRS). This example demonstrates the large volumetric coverage and high spatial resolution achievable using radial 4D flow MRI and the heterogeneity in vascular anatomy seen in these patients.

Figure 6.

Average blood flow in different vessels over 6 visits for patients and healthy volunteers. Solid: patient; dotted: healthy. Error bars indicate ± standard deviations.