F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA.
The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
Magn Reson Med. 2022 Aug;88(2):757-769. doi: 10.1002/mrm.29247. Epub 2022 Apr 5.
The traditional radiofrequency (RF)-prepared B mapping technique consists of one scan with an RF preparation module for flip angle-encoding and a second scan without this module for normalizing. To reduce the T -induced k-space filtering effect, this method is limited to 2D FLASH acquisition with a two-parameter method. A novel 3D RF-prepared three-parameter method for ultrafast B -mapping is proposed to correct the T -induced quantification bias.
The point spread function analysis of FLASH shows that the prepared longitudinal magnetization before the FLASH acquisition and the image signal obeys a linear (not proportional) relationship. The intercept of the linear function causes the quantification bias and can be captured by a third saturated scan.
Using the 2D double-angle method (DAM) as the reference, a 3D RF-prepared three-parameter protocol with 9 s duration was compared with the two-parameter method, as well as the saturated DAM (SDAM) method, the dual refocusing echo acquisition mode (DREAM) method, and the actual flip-angle imaging (AFI) method, for B mapping of brain, breast, and abdomen with different orientations and shim settings at 3T.
The 3D RF-prepared three-parameter method with complex-subtraction delivered consistently lower RMS error, error mean, error standard deviation, and higher concordance correlation coefficients values than the two-parameter method, the three-parameter method with magnitude-subtraction, the multi-slice DREAM and the 3D AFI, and were close to the results of 2D or multi-slice SDAM.
The proposed ultrafast 3D RF-prepared three-parameter method with complex-subtraction was demonstrated with high accuracy for B mapping of brain, breast, and abdomen.
传统的射频（RF）准备 B 映射技术包括一个带有 RF 准备模块的扫描，用于翻转角编码，以及一个没有该模块的第二个扫描，用于归一化。为了减少 T 引起的 k 空间滤波效应，该方法仅限于二维 FLASH 采集，采用双参数方法。本文提出了一种新的用于超快 B 映射的 3D RF 准备三参数方法，以校正 T 引起的定量偏差。
FLASH 的点扩散函数分析表明，FLASH 采集前的准备纵向磁化强度和图像信号之间存在线性（非比例）关系。线性函数的截距导致定量偏差，可以通过第三个饱和扫描来捕获。
以 2D 双角度法（DAM）为参考，比较了 3D RF 准备三参数协议（用时 9 秒）与双参数法，以及饱和 DAM（SDAM）法、双重聚焦回波采集模式（DREAM）法和实际翻转角成像（AFI）法，用于不同方位和匀场设置的脑、乳腺和腹部的 B 映射。
与双参数法、三参数法的幅度相减、多层面 DREAM 和 3D AFI 相比，具有复数相减的 3D RF 准备三参数法具有更低的均方根误差、误差均值、误差标准差和更高的一致性相关系数值，且接近 2D 或多层面 SDAM 的结果。
本文提出的超快 3D RF 准备三参数法具有复数相减，用于脑、乳腺和腹部的 B 映射具有高精度。
