The Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland.
F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland.
Magn Reson Med. 2019 Jun;81(6):3544-3554. doi: 10.1002/mrm.27668. Epub 2019 Feb 8.
Velocity-selective saturation (VSS) pulse trains provide a viable alternative to the spatially selective methods for measuring cerebral blood volume (CBV) by reducing the sensitivity to arterial transit time. This study is to compare the Fourier-transform-based velocity-selective saturation (FT-VSS) pulse trains with the conventional flow-dephasing VSS techniques for CBV quantification.
The proposed FT-VSS label and control modules were compared with VSS pulse trains utilizing double refocused hyperbolic tangent (DRHT) and 8-segment B1-insensitive rotation (BIR-8). This was done using both numerical simulations and phantom studies to evaluate their sensitivities to gradient imperfections such as eddy currents. DRHT, BIR-8, and FT-VSS prepared CBV mapping was further compared for velocity-encoding gradients along 3 orthogonal directions in healthy subjects at 3T.
The phantom studies exhibited more consistent immunity to gradient imperfections for the utilized FT-VSS pulse trains. Compared to DRHT and BIR-8, FT-VSS delivered more robust CBV results across the 3 VS encoding directions with significantly reduced artifacts along the superior-inferior direction and improved temporal signal-to-noise ratio (SNR) values. Average CBV values obtained from FT-VSS based sequences were 5.3 mL/100 g for gray matter and 2.3 mL/100 g for white matter, comparable to literature expectations.
Absolute CBV quantification utilizing advanced FT-VSS pulse trains had several advantages over the existing approaches using flow-dephasing VSS modules. A greater immunity to gradient imperfections and the concurrent tissue background suppression of FT-VSS pulse trains enabled more robust CBV measurements and higher SNR than the conventional VSS pulse trains.
速度选择饱和（VSS）脉冲序列通过减少对动脉渡越时间的敏感性，为测量脑血容量（CBV）提供了一种可行的替代空间选择方法。本研究旨在比较基于傅里叶变换的速度选择饱和（FT-VSS）脉冲序列与传统的流动去相位 VSS 技术在 CBV 定量中的应用。
将所提出的 FT-VSS 标记和控制模块与利用双重反转双曲线正切（DRHT）和 8 段 B1 不敏感旋转（BIR-8）的 VSS 脉冲序列进行比较。这是通过数值模拟和体模研究来完成的，以评估它们对梯度不完美（如涡流）的敏感性。在 3T 健康受试者中，进一步比较了 DRHT、BIR-8 和 FT-VSS 制备的 CBV 映射在 3 个正交方向上的流速编码梯度。
体模研究显示，所使用的 FT-VSS 脉冲序列对梯度不完美具有更一致的抗干扰能力。与 DRHT 和 BIR-8 相比，FT-VSS 在 3 个 VS 编码方向上提供了更稳健的 CBV 结果，沿上下方向的伪影显著减少，时间信号噪声比（SNR）值提高。从基于 FT-VSS 的序列获得的平均 CBV 值为灰质 5.3 mL/100 g，白质 2.3 mL/100 g，与文献预期值相当。
利用先进的 FT-VSS 脉冲序列进行绝对 CBV 定量具有优于现有使用流动去相位 VSS 模块的方法的几个优点。FT-VSS 脉冲序列对梯度不完美的更高免疫力以及同时对组织背景的抑制作用，使 CBV 测量更稳健，SNR 更高，优于传统的 VSS 脉冲序列。
