Oh Tong In, Koo Hwan, Lee Kyung Heon, Kim Sang Min, Lee Jeehyun, Kim Sung Wan, Seo Jin Keun, Woo Eung Je
Department of Medical Physics and Bioengineering, University College London, UK.
Physiol Meas. 2008 Mar;29(3):295-307. doi: 10.1088/0967-3334/29/3/002. Epub 2008 Feb 11.
Validation and interpretation of reconstructed images using a multi-frequency electrical impedance tomography (mfEIT) requires a conductivity phantom including imaging objects with known complex conductivity (sigma + iomegaepsilon) spectra. We describe imaging experiments using the recently developed mfEIT system called the KHU Mark1 with the frequency range of 10 Hz to 500 kHz. Using a bio-impedance spectroscopy (BIS) system, we first measured complex conductivity spectra of different imaging objects including saline, agar, polyacrylamide, TX151, animal hide gelatin, banana and cucumber. Based on an analysis of how conductivity and permittivity affect measured complex boundary voltages, we suggested a new complex version of a multi-frequency time-difference image reconstruction algorithm. Imaging experiments were conducted to produce time-difference images of the objects at multiple frequencies using the proposed algorithm. Images of a conductor (stainless steel) and an insulator (acrylic plastic) were used to set a common scale bar to display all images. Comparing reconstructed time-difference images at multiple frequencies with measured complex conductivity spectra, we found that they showed an overall similarity in terms of changes in complex conductivity values with respect to frequency. However, primarily due to the limitation of the difference imaging algorithm, we suggest that multi-frequency time-difference images must be interpreted in terms of relative contrast changes with respect to frequency. We propose further imaging studies using biological tissues of known complex conductivity spectra and using human subjects to find clinical applications of the mfEIT system.
使用多频电阻抗断层成像（mfEIT）对重建图像进行验证和解读需要一个电导率模型，该模型包含具有已知复电导率（σ + iωε）光谱的成像对象。我们描述了使用最近开发的名为KHU Mark1的mfEIT系统进行的成像实验，其频率范围为10 Hz至500 kHz。使用生物电阻抗光谱（BIS）系统，我们首先测量了不同成像对象的复电导率光谱，这些对象包括盐水、琼脂、聚丙烯酰胺、TX151、动物皮明胶、香蕉和黄瓜。基于对电导率和介电常数如何影响测量的复边界电压的分析，我们提出了一种新的多频时间差图像重建算法的复数版本。使用所提出的算法进行成像实验，以生成多个频率下对象的时间差图像。使用导体（不锈钢）和绝缘体（丙烯酸塑料）的图像来设置一个通用的比例尺，以显示所有图像。将多个频率下重建的时间差图像与测量的复电导率光谱进行比较，我们发现它们在复电导率值随频率变化方面总体上具有相似性。然而，主要由于差分成像算法的局限性，我们建议多频时间差图像必须根据相对于频率的相对对比度变化来进行解读。我们提议进一步开展成像研究，使用具有已知复电导率光谱的生物组织并使用人体受试者，以找到mfEIT系统的临床应用。
