IEEE Trans Med Imaging. 2019 Feb;38(2):349-359. doi: 10.1109/TMI.2018.2865121. Epub 2018 Aug 13.
In magnetic resonance-based electrical properties tomography (EPT), circularly polarized magnetic field B from a transmit radiofrequency (RF) coil is measured and utilized to infer the electrical conductivity and permittivity of biological tissues. Compared with a quadrature RF coil, a multi-channel transmit coil provides a plurality of unique transmit B patterns that help to alleviate the under-determinedness of EPT reconstruction problem, and it also allows to circumvent the "transceive phase assumption" that fails at ultra-high-field MRI. Here, a new approach, contrast conformed electrical properties tomography or CONCEPT, is proposed based on the multi-channel transmission that retrieves electrical properties (EPs) by solving a linear partial differential equation with discriminated L and L norm regularization informed by intermediate EP gradient. The theory of CONCEPT and a fast reconstruction algorithm based on the alternating direction method of multipliers are described and evaluated using numerical simulations, phantom experiment, and analysis of in vivo human brain data at 7 T MRI. Compared with the multi-channel gradient-based EPT (gEPT) method, this new technology does not require receive- B sensitivity profiles and does not rely on symmetry assumption regarding RF coil design and imaged target. Moreover, it is not dependent on external prior information, such as integration seed point or anatomical MRI, which can be sources of bias in reconstructed EP values. By deriving EPs from transmit B profiles only, CONCEPT can be used with RF coils that include receive-only arrays with large channel count which can, in turn, offer substantial gains in signal-to-noise ratio. It also holds potentials to image unsymmetrical body organs and diseased brain. CONCEPT provides solutions for the practical problems during the implementation of gEPT, thus representing a more generalized framework in the context of multi-channel RF transmission.
在基于磁共振的电特性层析成像（EPT）中，通过发射射频（RF）线圈测量并利用圆极化磁场 B 来推断生物组织的电导率和介电常数。与正交 RF 线圈相比，多通道发射线圈提供了多个独特的发射 B 模式，有助于缓解 EPT 重建问题的欠定性，并且还可以避免在超高场 MRI 中失效的“收发相位假设”。在这里，提出了一种新的方法，对比一致电特性层析成像或 CONCEPT，该方法基于多通道传输，通过求解带有区分 L 和 L 范数正则化的线性偏微分方程，并利用中间 EP 梯度的信息来恢复电特性（EPs）。描述并评估了 CONCEPT 的理论和基于交替方向乘子法的快速重建算法，使用数值模拟、体模实验和 7T MRI 分析人体大脑数据进行了评估。与多通道基于梯度的 EPT（gEPT）方法相比，这项新技术不需要接收 B 灵敏度分布，也不依赖于 RF 线圈设计和成像目标的对称性假设。此外，它不依赖于外部先验信息，例如积分种子点或解剖 MRI，这些信息可能会导致重建 EP 值产生偏差。通过仅从发射 B 分布中得出 EP，CONCEPT 可与仅包含大量通道数的接收 RF 线圈一起使用，从而在信号噪声比方面提供实质性的增益。它还具有对不对称身体器官和患病大脑成像的潜力。CONCEPT 为 gEPT 实施过程中的实际问题提供了解决方案，因此在多通道 RF 传输的背景下代表了更通用的框架。
