Introduction

DWI is the non-invasive technique to detect the diffusion movement of water molecules in living tissues. IVIM can distinguish the diffusion signal of Brownian motion of water molecules in tissues from the perfusion signal formed by capillary microcirculation, and is helpful to better describe the complex signal attenuation modes in biological tissues and organs [4]. 4D flow MRI with motion encoding and volumetric and isotropic acquisition achieves quantification of blood flow directions, velocities, wall shear force and pressures in the relatively large vessels, such as portal vein [5]. The purpose of this study is to assess the possible correlation the perfusion paraments and quantitative values of blood flow using liver IVIM and portal vein 4D flow-MRI for cirrhosis patients.

Methods

This study has been approved by the institutional IRB. 11 patients were recruited with informed consent acquired from each subject. All patients were scanned using a 3.0 T MR scanner (Ingenia CX, Philips Healthcare, the Netherlands) with a 16-channel abdominal array coil. The MR protocols include T1WI, T2WI, DWI, IVIM, 4D Flow and DYNAMIC sequence. For 4D Flow imaging, a 2D phase-contrast scan was performed first (axial, TR/TE = 4.4/2.7 ms, FOV = 200×200 mm2, resolution = 1.5×1.5×8 mm3, PC direction = RL, PC velocity = 200 cm/s, scan time = 13 s) to measure the flow velocity in the portal vein, as a reference for velocity encodings (VENC). The 4D Flow sequence with 8-fold compressed sensing acceleration was scanned with the following parameters: axial, TR/TE = 5.0/3.2 ms, FOV = 300×350 mm2, resolution = 2.5×2.5×2.5 mm3, PC direction = RL-AP-FH, VENC = 30 cm/s, scan time = 4min37s. The detailed parameters for all the other sequences were listed in Table 1. After the MR scan is completed, the 4D flow images were processed on CVI42 package (Canada Circle Cardiovascular Imaging）by an experienced radiologist to obtain the 3D angiogram. Four planes were manually placed vertical on the targeted vessel segments to measure the flow direction，the flow rate (cm/s), the axial-wall shear stress (WSS, Pa), and the pressure gradient (mmHg). Three planes were placed at the proximal, middle, and distal of the main portal vein and one at the splenic vein confluence as reference (Figure1). The images of other sequences were analyzed on a post-processing ISP workstation (Intelli Space Portal, Philips Healthcare) to measure IVIM parameters included: sADC, D, D* and F (Figure2). Spearman test (SPSS 22.0) was used to analyze the correlation between IVIM parameters and 4D flow-MRI parameters.

Results

sADC and D values were negatively correlated with the proximal Flow rate (r=0.626, P＜0.05) and the middle Flow rate (r=0.709, P＜0.05), respectively. D* value was positively correlated with the middle Flow and proximal Flow rate (r=0.900, P=0.037). There was no correlation among the other parameters (P＞0.05).

Discussion and Conclusion

The changes in portal blood flow during the development of liver cirrhosis were associated with the variation of the signals in intrahepatic blood flow. There is a certain correlation among sADC and D values measured by IVIM and flow rate in 4D flow sequences. The mechanism behind this correlation need the further investigation and may shed light on the disease assessment and the development of novel therapies.

Acknowledgements

No acknowledgement found.