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2015 ; 9
(2
): 0210011-210018
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Design of Bioimpedance Spectroscopy Instrument With Compensation Techniques for
Soft Tissue Characterization
#MMPMID26029317
Dodde RE
; Kruger GH
; Shih AJ
J Med Device
2015[Jun]; 9
(2
): 0210011-210018
PMID26029317
show ga
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 ?V through 100 kHz while maintaining an
output impedance of 1 M? 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.