Department of Experimental Physics 5, University of Würzburg, Würzburg, Germany.
Magn Reson Med. 2012 Aug;68(2):507-15. doi: 10.1002/mrm.23232. Epub 2011 Dec 21.
Bloch-Siegert (BS) based B(1)(+) mapping methods use off-resonant pulses to encode quantitative B(1)(+) information into the signal phase. It was recently shown that the principle behind BS-based B(1)(+) mapping can be expanded from spin echo (BS-SE) and gradient-echo (BS-FLASH) based BS B(1)(+) mapping to methods such as Carr, Purcell, Meiboom, Gill (CPMG)-based turbo-spin echo (BS-CPMG-TSE) and multi-spin echo (BS-CPMG-MSE) imaging. If CPMG conditions are preserved, BS-CPMG-TSE allows fast acquisition of the B(1)(+) information and BS-CPMG-MSE enables simultaneous mapping of B(1)(+), M(0), and T(2). To date, however, two separate MRI experiments must be performed to enable the calculation of B(1)(+) maps. This study investigated a modified encoding strategy for CPMG BS-based methods to overcome this limitation. By applying a "bipolar" off-resonant BS pulse before the refocusing pulse train, the needed phase information was able to be encoded into different echo images of one echo train. Thus, this technique allowed simultaneous B(1)(+) and T(2) mapping in a single BS-CPMG-MSE experiment. To allow single-shot B(1)(+) mapping, this method was also applied to turbo-spin echo imaging. Furthermore, the presented modification intrinsically minimizes phase-based image artifacts in BS-CPMG-TSE experiments.
基于布洛赫-西格特（BS）的 B(1)(+)映射方法使用离共振脉冲将定量 B(1)(+)信息编码到信号相位中。最近表明，BS 基 B(1)(+)映射背后的原理可以从自旋回波（BS-SE）和梯度回波（BS-FLASH）扩展到基于 Carr、Purcell、Meiboom、Gill（CPMG）的涡轮自旋回波（BS-CPMG-TSE）和多自旋回波（BS-CPMG-MSE）成像方法。如果保持 CPMG 条件，BS-CPMG-TSE 允许快速获取 B(1)(+)信息，而 BS-CPMG-MSE 则能够同时映射 B(1)(+)、M(0)和 T(2)。然而，迄今为止，必须进行两次单独的 MRI 实验才能计算 B(1)(+)图谱。本研究探讨了一种改进的 CPMG BS 基方法的编码策略，以克服这一限制。通过在聚焦脉冲序列之前施加“双极”离共振 BS 脉冲，可以将所需的相位信息编码到一个脉冲序列的不同回波图像中。因此，该技术允许在单个 BS-CPMG-MSE 实验中同时进行 B(1)(+)和 T(2)映射。为了允许单次 B(1)(+)映射，该方法也应用于涡轮自旋回波成像。此外，所提出的改进从本质上最小化了 BS-CPMG-TSE 实验中基于相位的图像伪影。
