Design of Bioimpedance Spectroscopy Instrument With Compensation Techniques for Soft Tissue Characterization

Abstract

Bioimpedance spectroscopy (BIS) has shown significant potential in many areas of medicine to provide new physiologic markers. Several acute and chronic diseases are accompanied by changes in intra- and extracellular fluid within various areas of the human body. The estimation of fluid in various body compartments is therefore a simple and convenient method to monitor certain disease states. In this work, the design and evaluation of a BIS instrument are presented and three key areas of the development process investigated facilitating the BIS measurement of tissue hydration state. First, the benefit of incorporating DC-stabilizing circuitry to the standard modified Howland current pump (MHCP) is investigated to minimize the effect of DC offsets limiting the dynamic range of the system. Second, the influence of the distance between the bioimpedance probe and a high impedance material is investigated using finite element analysis (FEA). Third, an analytic compensation technique is presented to minimize the influence of parasitic capacitance. Finally, the overall experimental setup is evaluated through ex vivo BIS measurements of porcine spleen tissue and compared to published results. The DC-stabilizing circuit demonstrated its ability to maintain DC offsets at less than 650 μV through 100 kHz while maintaining an output impedance of 1 MΩ from 100 Hz to 100 kHz. The proximity of a bioimpedance probe to a high impedance material such as acrylic was shown to increase measured impedance readings by a factor of 4x as the ratio of the distance between the sensing electrodes to the distance between the bioimpedance probe and acrylic reached 1:3. The average parasitic capacitance for the circuit presented was found to be 712 ± 128 pF, and the analytic compensation method was shown to be able to minimize this effect on the BIS measurements. Measurements of porcine spleen tissue showed close correlation with experimental results reported in published articles. This research presents the successful design and evaluation of a BIS instrument. Specifically, robust measurements were obtained by implementing a DC-stabilized current source, investigating probe-material proximity issues and compensating for parasitic capacitance. These strategies were shown to provide tissue measurements comparable with published literature.

In vivocharacterization of ischemic small intestine using bioimpedance measurements

“…When measuring on soft tissue like the small intestine, exerting pressure on the intestinal walls not only affect the contact area, but can strongly influence the measured electrical properties (Dodde et al, 2012, Dodde et al, 2015, Moqadam et al, 2015. Pressure can also lead to mechanical displacement of the layered structures.…”

Novel 3D printed probe for bioimpedance spectroscopic measurement of oral mucosa: design and testing with ex vivo porcine oral tissues

“…BIS is now utilized in everyday clinical practice in intensive care and nutritional medicine, in the measurement of fluid volumes and determination of body composition [4,5]. It has also been found to be an affordable solution to investigate pathological tissue alterations such as skin cancer [6] and breast cancer [7]. Despite this, attempts to assess oral mucosa health status or oral mucosal diseases by using BIS have been rare [3,[8][9][10].…”

The feasibility of using compression bioimpedance measurements to quantify peripheral edema

“…3) was based on the tetrapolar BIS circuit designed and developed by Dodde et al [25,27,28,29]. Our system consisted of a BIS circuit, four platinum leaf probes, an oscilloscope (DSO7032B, Agilent Technologies, Santa Clara, CA), a single-axis programmable mechanical test stand (ESM301L, Mark-10, Copiague, NY), and a computer for automation and data acquisition.…”