Transit time ultrasound perivascular flow probe technology is superior to MR imaging on hepatic blood flow measurement in a porcine model.

BACKGROUND: The hepatic hemodynamics is an essential parameter in surgical planning as well as in various disease processes. The transit time ultrasound (TTUS) perivascular flow probe technology is widely used in clinical practice to evaluate the hepatic inflow, yet invasive. The phase-contrast-MRI (PC-MRI) is not invasive and potentially applicable in assessing the hepatic blood flow. In the present study, we compared the hepatic inflow rates using the PC-MRI and the TTUS probe, and evaluated their predictive value of post-hepatectomy adverse events. METHODS: Eighteen large white pigs were anaesthetized for PC-MRI and approximately 75% hepatic resection was performed under a unified protocol. The blood flow was measured in the hepatic artery (Qha), the portal vein (Qpv), and the aorta above the celiac trunk (Qca) using PC-MRI, and was compared to the TTUS probe. The Bland-Altman method was conducted and a partial least squares regression (PLS) model was implemented. RESULTS: The mean Qpv measured in PC-MRI was 0.55 ±â€¯0.12 L/min, and in the TTUS probe was 0.74 ±â€¯0.17 L/min. Qca was 1.40 ±â€¯0.47 L/min in the PC-MRI and 2.00 ±â€¯0.60 L/min in the TTUS probe. Qha was 0.17 ±â€¯0.10 L/min in the PC-MRI, and 0.13 ±â€¯0.06 L/min in the TTUS probe. The Bland-Altman method revealed that the estimated bias of Qca in the PC-MRI was 32% (95% CI: -49% to 15%); Qha 17% (95% CI: -15% to 51%); and Qpv 40% (95% CI: -62% to 18%). The TTUS probe had a higher weight in predicting adverse outcomes after 75% resection compared to the PC-MRI (ß= 0.35 and 0.43 vs ß = 0.22 and 0.07, for tissue changes and premature death, respectively). CONCLUSIONS: There is a tendency of the PC-MRI to underestimate the flow measured by the TTUS probes. The TTUS probe measures are more predictive of relevant post-hepatectomy outcomes.

Real-time 3D MRI of contrast agents in whole living mice.

A specific mouse whole body coil and a dedicated gradient system at 4.7 T were coupled with an ultra-fast 3D gradient echo MRI and keyhole reconstruction technique to obtain 3D whole-body dynamic T(1)-weighted or T(2)*-weighted imaging. The technique was used to visualize the real-time distribution of non-targeting T(1) and T(2)* contrast agent (CA) in a glioma-bearing mouse model. T(1) dynamic contrast-enhancement imaging was performed with a fast imaging with steady-state precession sequence [echo time/repetition time (TE/TR), 1.32/3.7 ms] before and after CA injection (Gd-DOTA and BSA-Gd-DOTA) for 21 min. The temporal resolution was 1 image/6.5 s. T(2)* imaging (TE/TR, 4/8 ms) was performed before and after iron-based (small and ultra-small particles of iron oxide) CA injection for 45 min. The temporal resolution was 1 image/14 s. Signal-to-noise ratio curves were determined in various mouse organs. The whole-body coil and gradient systems made it possible to acquire data with sufficient and homogeneous signal-to-noise ratio on the whole animal. The spatial resolution allowed adequate depiction of the major organs, blood vessels and brain glioma. The distribution and the time-course of T(1) and T(2)* contrasts upon contrast agent injection were also assessed. 3D whole-body mouse MRI is feasible at high spatial resolution in movie mode and can be applied successfully to visualize real-time contrast agent distribution. This method should be effective in future preclinical molecular imaging studies.