Effect of gravity on portal venous flow: Evaluation using multiposture MRI

Background Analysis of portal venous flow (PVF) is important when evaluating the severity and prognosis of liver disease. PVF might be altered by postural changes (ie, difference in the effects of gravity). Purpose To evaluate the effect of gravity on PVF using a novel MRI system, which can obtain abdominal MRIs in both the supine and the upright positions. Study Type Prospective self control. Subjects Twelve healthy young male volunteers. Field Strength/Sequence Caval velocity‐mapped images were obtained using the electrocardiography‐triggered cine phase‐contrast technique in the supine and upright positions with multiposture MRI (paired 0.4 T permanent magnets). Assessment The mean PVF velocity in the region of interest in each cardiac phase was determined. A PVF curve in the cardiac cycle was also obtained from the PVF velocity multiplied by the cross‐sectional area. The mean PVF velocity, maximum PVF velocity, cross‐sectional area of the PV, mean PVF, maximum PVF, and heart rate in the supine and upright positions were assessed. Statistical Tests Wilcoxon signed‐rank tests were applied. P < 0.05 was considered statistically significant. Results The mean PVF velocity, maximum PVF velocity, cross‐sectional area of the PV, and maximum PVF were all significantly lower in the upright position compared with the supine position (P = 0.002 for all), with differences of 42% ± 15%, 38% ± 12%, 60% ± 17%, 24% ± 11%, and 22% ± 9.3%, respectively. However, heart rate was significantly higher (116% ± 9.2%, P = 0.003) in the upright position compared with the supine position. Data Conclusion The effect of gravity during postural change from a supine to an upright position significantly decreases the PVF. Multiposture MRI allows acquisition of more detailed information on liver function. Level of Evidence: 2 Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2019;50:83–87.