Velocity Window for Detection of Flow with MR Phase Imaging

Lim, Tae Hwan; Tavares, Nuno J; Hylton, Nola M; Higgins, Charles B

Abstract

PURPOSE
To prepare a data base for semi-quantitative measurement of blood flow velocity on MR phase imaging technique by analyzing the characteristics of flow image according to the ranges of flow velocity.
MATERIALS AND METHODS
We obtained MR phase images of flow with velocity ranging from 0 to 70cm/sec. A straight flow tube with 2.09cm internal diameter and a flow tube with 75% stenosis were used as flow phantoms for this study. MR imagings were performed on a 0.35 T MR imaging system.
RESULTS
At a velocity of 0-3cm/sec, the MR phase signal proceeded from an equivocal phase change to a homogeneous intraluminal signal intensity. Ata flow velocity of 3.1cm/sec, first phase wrap occurred, and there were two phase wraps up to 15cm/sec of flow velocity. In this velocity range, the MR phase image revealed an isocentric circular target appearance. At a velocity range of 15-30cm/sec, three tofour phase wraps occurred, and the MR phase image showed a multiple target appearance. At a velocity above 30cm/sec, the MR phase image showed an irregular unstructured appearance and above 50cm/sec, there were no flow signals and only noise-like signals were observed. The flow phantom of the stenosis model demonstrated the same phase image pattern as the high velocity flow in the stenotic and post-stenotic areas. In the pre-stenotic area, acharacteristic reversed laminar flow profile was observed.
CONCLUSION
Flow velocity can be detected semiquantitatively as velocity ranges on MR phase imaging. The results of the experiment using a stenotic model suggest that MR phase imaging can be used as a modality for investigation of flow velocity and profiles.