Borthakur Arijitt, Charagundla Sridhar R, Wheaton Andrew, Reddy Ravinder
Department of Radiology, University of Pennsylvania, Philadelphia, PA, USA.
J Magn Reson. 2004 Apr;167(2):306-16. doi: 10.1016/j.jmr.2004.01.007.
T1rho-weighted MRI is a novel basis for generating tissue contrast. However, it suffers from sensitivity to B1 inhomogeneity. First, excitation with a spatially varying B1 causes flip-angle artifacts and second, spin locking with an inhomogeneous B1 results in non-uniform T1rho contrast. In this study, we overcome the former complication with a specially designed spin-locking pulse sequence and we successfully obtain T1rho-weighted images with a surface coil. In this pulse sequence, the spin-lock pulse was divided into segments of equal duration and alternating phase. This "self-compensating" T1rho-preparatory pulse sequence was analyzed and the effect of an inhomogeneous B1 field was simulated using the Bloch equations. T1rho-weighted MR images of a phantom and a human knee joint in vivo were obtained on a clinical scanner with a surface coil to demonstrate the utility of the pulse sequence. The self-compensating T1rho-prepared pulses sequence resulted in substantially reduced image artifacts compared to the conventional, single-phase spin-lock pulse.
T1rho加权磁共振成像（MRI）是产生组织对比度的一种新方法。然而，它对B1不均匀性敏感。首先，空间变化的B1激发会导致翻转角伪影，其次，不均匀B1的自旋锁定会导致T1rho对比度不均匀。在本研究中，我们通过专门设计的自旋锁定脉冲序列克服了前者的复杂性，并使用表面线圈成功获得了T1rho加权图像。在这个脉冲序列中，自旋锁定脉冲被分成等时长且相位交替的段。对这种“自补偿”T1rho准备脉冲序列进行了分析，并使用布洛赫方程模拟了不均匀B1场的影响。在配备表面线圈的临床扫描仪上获得了体模和人体膝关节的T1rho加权MR图像，以证明该脉冲序列的实用性。与传统的单相自旋锁定脉冲相比，自补偿T1rho准备脉冲序列显著减少了图像伪影。
