Division of Radiological Physics, Department of Radiology, University Hospital Basel, Basel, Switzerland.
Department of Biomedical Engineering, University of Basel, Basel, Switzerland.
Magn Reson Med. 2022 Mar;87(3):1250-1260. doi: 10.1002/mrm.29020. Epub 2021 Nov 9.
To present a new complex-valued B mapping method for electrical properties tomography using Carr-Purcell spin echoes.
A Carr-Purcell (CP) echo train generates pronounced flip-angle dependent oscillations that can be used to estimate the magnitude of B . To this end, a dictionary is used that takes into account the slice profile as well as T relaxation along the echo train. For validation, the retrieved B map is compared with the actual flip angle imaging (AFI) method in a phantom (79 ε , 0.34 S/m). Moreover, the phase of the first echo reflects the transceive phase. Overall, the CP echo train yields an estimate of the complex-valued B , allowing electrical properties tomography with both permittivity and conductivity. The presented method is evaluated in phantom scans as well as for in vivo brain at 3 T.
In the phantom, the obtained magnitude B maps retrieved from the CP echo train and the AFI method show excellent agreement, and both the reconstructed estimated permittivity (79 ± 3) ε and conductivity (0.35 ± 0.04) S/m values are in accordance with expectations. In the brain, the obtained electrical properties are also close to expectations. In addition to the retrieved complex B information, the decay of the CP echo trains also yields an estimate for T .
The CP sequence can be used to simultaneously provide both B magnitude and phase estimations, and therefore allows for full reconstruction of the electrical properties.
提出一种新的基于 Carr-Purcell 自旋回波的复值 B 映射方法，用于电特性层析成像。
Carr-Purcell（CP）回波序列会产生明显的翻转角依赖的振荡，可用于估计 B 的幅度。为此，使用了一个字典，该字典考虑了切片轮廓以及沿回波序列的 T 弛豫。为了验证，在体模（79 ε，0.34 S/m）中，将重建的 B 图与实际的翻转角成像（AFI）方法进行了比较。此外，第一个回波的相位反映了收发相位。总的来说，CP 回波序列可以估计复值 B，从而实现介电常数和电导率的电特性层析成像。所提出的方法在体模扫描以及 3T 下的活体大脑中进行了评估。
在体模中，从 CP 回波序列和 AFI 方法获得的 B 图的幅度图显示出极好的一致性，并且重建的估计介电常数（79 ± 3）ε和电导率（0.35 ± 0.04）S/m 值都符合预期。在大脑中，获得的电特性也接近预期。除了重建的复值 B 信息外，CP 回波序列的衰减还可以估计 T。
CP 序列可用于同时提供 B 幅度和相位估计，从而可以完全重建电特性。
