Department of Radiation Oncology, Sun Yat-sen Memorial Hospital, Sun Yat-sen University.
Department of Biomedical Engineering, Southern Medical University.
Magn Reson Med Sci. 2020 Feb 10;19(1):77-85. doi: 10.2463/mrms.mp.2018-0167. Epub 2019 Apr 24.
Magnetic resonance electrical property tomography (MR EPT) is a technique for non-invasively obtaining the electric property (EP) distribution of biological tissues, with a promising potential for application in the early detection of tumors. However, the contrast capability (CC) of this technique has not been fully studied. This work aims to theoretically explore the CC for detecting the variation of EP values and the size of the imaging region.
A simulation scheme was specifically designed to evaluate the CC of MR EPT. The simulation study has the advantage that the magnetic field can be accurately obtained. EP maps of the designed phantom embedded with target regions of designated various sizes and EPs were reconstructed using the homogeneous Helmholtz equation based on B with different signal-to-noise ratios (SNRs). The CC was estimated by determining the smallest detectable EP contrast when the target region size was as large as the Laplacian kernel and the smallest detectable target region size when the EP contrast was the same as the difference between healthy and malignant tissues in the brain, based on the reconstructed EP maps.
Using noise free B, the smallest detectable contrast and contrast were 1% and 3%, respectively, and the smallest detectable target region size was 1 mesh unit (the base unit size used in the simulation) for conductivity and relative permittivity. The smallest detectable EP contrast and target region size were decreased as the B SNR increased.
The CC of MR EPT was related with the SNR of the magnetic field. A small EP contrast and size were necessary for detection at a high-SNR magnetic field. Obtaining a high-SNR magnetic field is important for improving the CC of MR EPT.
磁共振电阻抗断层成像（MR EPT）是一种非侵入式获取生物组织电特性（EP）分布的技术，在肿瘤的早期检测中具有广阔的应用前景。然而，该技术的对比度能力（CC）尚未得到充分研究。本工作旨在从理论上探讨检测 EP 值变化和成像区域大小的 CC。
专门设计了一种模拟方案来评估 MR EPT 的 CC。模拟研究的优点是可以准确获得磁场。使用基于不同信噪比（SNR）的 B 相同的均匀亥姆霍兹方程，对设计的包含指定大小和 EP 的目标区域的幻影进行 EP 图重建。根据重建的 EP 图，当目标区域大小与拉普拉斯核相同时，以及当 EP 对比度与大脑中健康和恶性组织之间的差异相同时，确定最小可检测 EP 对比度和对比度，通过确定最小可检测目标区域大小来估计 CC。
在无噪声 B 的情况下，最小可检测对比度和对比度分别为 1%和 3%，对于电导率和相对介电常数，最小可检测目标区域大小为 1 个网格单元（模拟中使用的基本单元大小）。随着 B SNR 的增加，最小可检测 EP 对比度和目标区域大小减小。
MR EPT 的 CC 与磁场的 SNR 有关。在高 SNR 磁场下检测需要较小的 EP 对比度和大小。获得高 SNR 磁场对于提高 MR EPT 的 CC 很重要。
