Choi Bup Kyung, Oh Tong In, Sajib Saurav Zk, Kim Jin Woong, Kim Hyung Joong, Kwon Oh In, Woo Eung Je
Department of Biomedical Engineering, Kyung Hee University, Yongin, Korea.
Impedance Imaging Research Center, Kyung Hee University, Seoul, Korea.
Int Neurourol J. 2017 Apr;21(Suppl 1):S32-38. doi: 10.5213/inj.1734878.439. Epub 2017 Apr 21.
To realistically map the electric fields of biological tissues using a diffusion tensor magnetic resonance electrical impedance tomography (DT-MREIT) method to estimate tissue response during electrical stimulation.
Imaging experiments were performed using chunks of bovine muscle. Two silver wire electrodes were positioned inside the muscle tissue for electrical stimulation. Electric pulses were applied with a 100-V amplitude and 100-μs width using a voltage stimulator. During electrical stimulation, we collected DT-MREIT data from a 3T magnetic resonance imaging scanner. We adopted the projected current density method to calculate the electric field. Based on the relation between the water diffusion tensor and the conductivity tensor, we computed the position-dependent scale factor using the measured magnetic flux density data. Then, a final conductivity tensor map was reconstructed using the multiplication of the water diffusion tensor and the scale factor.
The current density images from DT-MREIT data represent the internal current flows that exist not only in the electrodes but also in surrounding regions. The reconstructed electric filed map from our anisotropic conductivity tensor with the projected current density shows coverage that is more than 2 times as wide, and higher signals in both the electrodes and surrounding tissues, than the previous isotropic method owing to the consideration of tissue anisotropy.
An electric field map obtained by an anisotropic reconstruction method showed different patterns from the results of the previous isotropic reconstruction method. Since accurate electric field mapping is important to correctly estimate the coverage of the electrical treatment, future studies should include more rigorous validations of the new method through and experiments.
使用扩散张量磁共振电阻抗断层成像（DT-MREIT）方法真实地绘制生物组织的电场，以估计电刺激期间的组织反应。
使用牛肌肉块进行成像实验。将两根银线电极置于肌肉组织内进行电刺激。使用电压刺激器施加幅度为100V、宽度为100μs的电脉冲。在电刺激期间，我们从一台3T磁共振成像扫描仪收集DT-MREIT数据。我们采用投影电流密度法计算电场。基于水扩散张量与电导率张量之间的关系，利用测量的磁通密度数据计算位置相关的比例因子。然后，通过水扩散张量与比例因子相乘重建最终的电导率张量图。
DT-MREIT数据的电流密度图像显示了不仅存在于电极中而且存在于周围区域的内部电流流动。由于考虑了组织各向异性，我们基于各向异性电导率张量和投影电流密度重建的电场图显示，其覆盖范围比以前的各向同性方法宽两倍多，电极和周围组织中的信号也更高。
通过各向异性重建方法获得的电场图显示出与以前各向同性重建方法不同的模式。由于准确的电场映射对于正确估计电治疗的覆盖范围很重要，未来的研究应通过……和……实验对新方法进行更严格的验证。
