Effect of Angulation between Aorta and Renal Artery on Signal Void of Proximal Renal Artery on MR Angiography:Phantom Study

Choi, Byoung Wook; Kim, Myung Joon; Jeong, Eun Kee; Hong, Seong Joon; Kong, Hae Young; Lee, Sam Hyeon

Abstract

PURPOSE: To determine the effect of anglulation between aorta the and renal artery on signal loss in theproximal renal artery, as seen on magnetic resonance angiography by phantom study using a pulsatile flow model. MATERIALS AND METHODS: Three phantoms of aorta and renal artery with angulation of 90 degree, 60 degree, and 30 degree wereobtained. Pulsatile recirculating flow (44%W/W glycerin, 60bpm) was used for MR angiography. First, axial 3D-TOFimages were obtained and reconstructed. MIP images were analyzed for the presence, area, and location of signalloss. 2D-PC images were obtained perpendicularly to the renal artery at a distance of 0, 4, 8 and 12mm from theostium. To calculate mean signal intensity of the renal artery, a ROI was drawn on 2D-PC images. To correlatesignal loss in 3D-TOF images with signal decrease in 2D-PC, we analyzed changes in signal intensity during onepulse cycle according to change of angulation and distance from the ostium of the renal artery by the calculatedvalues of relative signal decrease and ratio of signal decrease. RESULTS: A signal loss was observed up to 4mmfrom the ostium of the renal artery only in the case of the 90 degree phantom. Because the signal intensity measured inthe 2D-PC image of the 90 degree phantom was higher than that of the 60 degree phantom the signal loss observed in the3D-TOF images of the 90 degree phantom could not be explained by the magnitude of measured signal intensity alone.Relative signal decrease only at a distance of 0 and 4mm in the 90 degree phantom was evenly increased through a pulsecycle and the ratio of signal decrease at the same location was more than 50%. In contrast to the results of the90 degree phantom, those of 60 degree and 30 degree showed decreased of signal intensity mainly during the diastolic phase.CONCLUSION: Signal loss should become apparent at a certain angle between 60 degree and 90 degree. Decreased signalintensity causing signal loss in 3D-TOF was maintained throughout the systolic and diastolic phase of a pulsatilecycle and correlated with the ratio of signal decrease.