Flow Preparation Pulse for Abdominal Non-Contrast-Enhanced MRA

M. Miyoshi, T. Tsukamoto GE Yokogawa Medical Systems, Hino, Tokyo, Japan Abstract Steady State Free Precession (SSFP) yields high blood signal image in short scanning time and it enables Non-Contrast-Enhanced MR Angiography (NCE-MRA) in abdomen. However, SSFP produces bright signal not only in artery but also in vein or stationary fluids. We propose new Flow Preparation (Flow Prep) pulse to distinguish artery from vein and stationary fluids. This technique was developed based on bipolar velocity encoding (VENC) used in Phase Contrast Angiography. Phantom examination showed that signal intensity of the Flow Prep matched with theoretical values. The Flow Prep enhanced the contrast of artery in volunteer scans. Introduction SSFP can be used for abdominal NCE-MRA because of its high artery signal. However, vein and stationary fluid suppression is required. Yamashita et al. tried combination of inversion recovery and image subtraction [1]. They made subtraction image between images with non-selective IR pulse and with selective IR pulse and fast in-flow artery was depicted. However, subtraction method is sensitive to motion and it doubles scanning time. We propose Flow Prep in which contrast depends on flow velocity. This method doesn’t use image subtraction. Methods Pulse sequence chart of the Flow Prep is shown in figure 1. Non-selective RF pulses sandwich the VENC gradients. As the RF pulse sequence is base on CPMG, it’s not sensitive to magnetic field inhomogeneity and chemical shift. Magnetization vectors are also illustrated in figure 1. Stationary magnetization (black arrow) is not rotated with the VENC pulse (4) and it is flipped to My axis (6). On the other hand, flow magnetization (red arrow) is rotated by the VENC and is flipped back to Mz axis. Then a dephaser gradient pulse crushes transverse magnetization (7). As a result, longitudinal signal intensity after the Flow Prep is a function of the flow velocity (Eq. 1). ; 2 / )) cos( 1 ( 0 θ − × = M signal where τ is bipolar pulse time interval (2ms) and