The purpose of this study was to evaluate hemodynamic changes in the mesenteric and portal circulation of LDLT donors in response to surgical liver resection. Liver transplantation (LT) is a highly successful and definitive treatment for patients with liver failure, and in some cases, hepatocellular carcinoma. However, over the last two decades, there has been a steady decline in the supply of organs from deceased donors. This shortage has motivated the implementation of living donor liver transplantation (LDLT), as an alternative to cadaveric transplantation¹. Success rates with LDLT are comparable to cadaveric liver transplants. However, little is known about the effects that LDLT has on the hemodynamics of the remaining liver in the donor. Therefore, the purpose of this study was to evaluate hemodynamic changes in the mesenteric and portal circulation of LDLT donors in response to surgical liver resection.

In this IRB-approved and HIPAA-compliant study, 4 LDLT donors (2M, 2F; 33-53 years; 68-86 Kg) were imaged after written informed consent before and within one month after surgery (3 patients right lobe and 1patient left lateral lobe resection). Subjects were scanned after at least 5 hours of fasting (pre-surgery) to avoid variability in splanchnic flow after a meal². MR-Imaging: Studies were conducted on a clinical 3T scanner (Discovery MR 750, GE Healthcare, Waukesha, WI) with a 32-chanel body coil (NeoCoil, Pewaukee, WI). 4D velocity mapping was achieved using a cardiac-gated time-resolved 3D radially undersampled phase contrast acquisition (5-point PC-VIPR) with increased velocity sensitivity performance^3,4. Radial 4D flow MRI image parameters included: imaging volume: 32x32x24cm spherical, 1.25mm acquired isotropic spatial resolution, TR/TE=6.4/2.2ms. All subjects received 0.05 mmol/kg of gadoxetic acid (Eovist, Bayer Healthcare, Wayne, NJ)). Pre- and post-surgery 4D flow MRI imaging protocols were identical. 4D flow MRI Data Analysis: Vessel segmentation was performed in MIMICs (Materialize, Leuven, Belgium) from PC angiograms and manual placement of cut-planes in the vessel of interest in EnSight (CEI, Apex, NC) where flow measurements and visualizations were conducted. Flow, peak velocity and cross sectional area of the vessel were quantified at the Superior Mesenteric Vein (SMV), Splenic Vein (SV), Left (LPV), right (RPV) and Main Portal Vein (PV) as well as Hepatic (HA) and Splenic Artery (SA) (Figures 1 and 2). Statistics:). Flow values measured in each vessel were compared before and after the surgery using paired Student t-tests. A p-value of 0.05 was chosen to indicate statistical significance.

SMV, SV, PV, LPV, RPV, HA and SA flows were successfully quantified in all subjects. Statistically significant increase in blood flow was seen in the LPV (146.6 ± 75.5 vs 969.4 ± 375.4 ml/s; p=0.002) after the surgery (n=3). The same trend of increased flow after surgery was seen in all vessels, however this increase was not statistically significant (Fig3). Significant increase in peak velocity was seen in the SMV (27.5 ± 8.6 vs 45.5 ± 7.3 cm/s; p=0.02), SV (30 ± 6.7 vs 47 ±11.7 cm/s; p=0.04), LPV (20 ± 6.9 vs 49.8 ± 9.6 cm/s; p=0.002) and SA (37.5 ± 13.9 vs 59.2 ±11.1 cm/s; p=0.05) (Fig4). The cross-sectional area of the vessels, particularly the remaining branch portal vein (LPV or RPV), also demonstrated increase. Even though there was an increase in the cross sectional area of all the vessels of interest, the only vessel that showed a significant increase in the cross sectional area was the LPV (34 ± 8.5 vs 100.1 ± 10.3 mm²; p=0.01) (n=3) (Fig5). In the specific case of the left lateral lobe resection, the right portal venous flow increased (574.4 vs 1203.9 ml/s), the peak velocity in the RPV also increased (31 vs 37 cm/s) as well as the RPV cross sectional area (63.6 vs 201.6 mm²).

The ability to quantify hemodynamic changes in the portal and mesenteric circulation non-invasively demonstrates that 4D flow MRI may be a suitable tool for both surgical planning of LDLT, and for improved understanding of the hemodynamic changes that occur in the liver remnant of the donor. Not surprisingly, we encountered highly patient-specific responses to each surgical procedure. However based on these highly encouraging results we are currently enrolling additional patients to investigate the use of 4D flow MRI for improved characterization of the liver hemodynamics after liver donation.