Haider S, Hrbek A, Xu Y
Department of Physics, Ryerson University, Toronto, Canada.
Physiol Meas. 2008 Jun;29(6):S41-50. doi: 10.1088/0967-3334/29/6/S04. Epub 2008 Jun 10.
Primarily this report outlines our investigation on utilizing magneto-acousto-electrical-tomography (MAET) to image the lead field current density in volume conductors. A lead field current density distribution is obtained when a current/voltage source is applied to a sample via a pair of electrodes. This is the first time a high-spatial-resolution image of current density is presented using MAET. We also compare an experimental image of current density in a sample with its corresponding numerical simulation. To image the lead field current density, rather than applying a current/voltage source directly to the sample, we place the sample in a static magnetic field and focus an ultrasonic pulse on the sample to simulate a point-like current dipole source at the focal point. Then by using electrodes we measure the voltage/current signal which, based on the reciprocity theorem, is proportional to a component of the lead field current density. In the theory section, we derive the equation relating the measured voltage to the lead field current density and the displacement velocity caused by ultrasound. The experimental data include the MAET signal and an image of the lead field current density for a thin sample. In addition, we discuss the potential improvements for MAET especially to overcome the limitation created by the observation that no signal was detected from the interior of a region having a uniform conductivity. As an auxiliary we offer a mathematical formula whereby the lead field current density may be utilized to reconstruct the distribution of the electrical impedance in a piecewise smooth object.
本报告主要概述了我们利用磁声电层析成像（MAET）对体导体中的导联场电流密度进行成像的研究。当通过一对电极向样品施加电流/电压源时，可获得导联场电流密度分布。这是首次使用MAET呈现高空间分辨率的电流密度图像。我们还将样品中电流密度的实验图像与其相应的数值模拟进行了比较。为了对导联场电流密度进行成像，我们不是直接向样品施加电流/电压源，而是将样品置于静磁场中，并将超声脉冲聚焦在样品上，以模拟焦点处的点状电流偶极子源。然后，我们使用电极测量电压/电流信号，根据互易定理，该信号与导联场电流密度的一个分量成正比。在理论部分，我们推导了将测量电压与导联场电流密度以及超声引起的位移速度相关联的方程。实验数据包括MAET信号和薄样品的导联场电流密度图像。此外，我们讨论了MAET的潜在改进，特别是为了克服在具有均匀电导率的区域内部未检测到信号这一局限性。作为辅助内容，我们提供了一个数学公式，通过该公式可以利用导联场电流密度重建分段光滑物体中的电阻抗分布。
