Purpose

Portal venous flow (PVF) is clinically important in liver function.^{1, 2} PVF may be affected by gravity, ie., it depends on body posture, but this has yet to be confirmed. In this study, we evaluated the effect of gravity on PVF in people in the supine and upright positions using an original magnetic resonance imaging (MRI) system that can obtain images in any posture (multi-posture MRI).

Materials and Methods

Caval velocity-mapped images in eight healthy volunteers were obtained with ECG-triggered cine phase-contrast technique in the supine and upright positions using multi-posture MRI (Fig. 1). The mean PVF velocity in the region of interest in each cardiac phase was determined after correction by subtraction of the baseline offset due to eddy currents. In addition, a PVF curve in the cardiac cycle was obtained from the PVF-velocity multiplied by the cross-sectional area, and the PVF volume was calculated by integration of the PVF curve in the cardiac cycle. The maximum PVF (PVF_max), PVF velocity, PVF volume, and cross-sectional area of the portal vein in the supine and upright positions were assessed.

Results and Discussion

The mean PVF velocity in the upright position (1.96 ± 1.29 cm/sec) was significantly lower than that in the supine position (10.1 ± 3.06 cm/sec) (P < .05) (Fig. 2a). The mean PVF volume in the upright position (87.2 ± 46.2 mL/min) was significantly lower than that in the supine position (854 ± 374 mL/min) (P < .05) (Fig. 2b). The PVF_max in the upright position (16.5 ± 5.30 mL/min) was significantly lower than that in the supine position (92.2 ± 34.9 mL/min) (P < .05) (Fig. 2c). These results indicate that gravity reduced the PVF velocity and volume, and these differences between postures potentially provide new diagnostic information on the compensatory faculty of gravity as compared with standard PVF measurements. In addition, the mean cross-sectional area in the upright position (90.1 ± 37.4 mm²) was significantly lower than that in the supine position (125 ± 30.1 mm²) (P < .05) because of the regulation of the portal pressure (Fig. 2d).

Conclusion

Gravity reduces PVF velocity and volume. Multi-posture MRI makes it possible to evaluate the effect of gravity on PVF.

Acknowledgements

No acknowledgement found.