MECHANICAL IMPEDANCE
OF BIOLOGICAL SOFT TISSUES

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Measuring means
Experimental study
Spectral measurements
Single-frequency measurements
Physical models
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E-mail: eugene@appl.sci-nnov.ru
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Radiophysics in medicine
IAP RAS

MEASURING MEANS

The first experiments with registration of impedance characteristics of biological tissues were performed on the stationary laboratory setup, based on vibration-exciting and vibration-measuring equipment of the Bruel & Kjer company (fig.1), firstly by the method of single-frequency vibration excitement, then by the method of noise-type vibration excitement and registration of frequency dependencies by the facilities of spectra analyzer. For the expansion of the experimental studies outside of laboratory the portable electronic devices (fig.2) were built subsequently, realizing the method of single-frequency measurement of impedance characteristics and their temporal dynamics monitoring in the course of various processes. This method was named as “Vibrational Viscoelastometry”. Else later the PC-based devices were built, realizing such measurements by the facilities of specialized programs.

Fig.1. “Vibrostend” Laboratory set	Fig.2. Vibrational Viscoelastometer VVEM-03	Fig.3. Myoviscoelastometer

The PC-based device of the first generation (fig.3) used the gauge VD-1 (fig.4a), the ISA interface card and operated in the MS DOS. The PC-based device of the second generation (fig.5) used the modified gauge VD-2 (fig.4b) and modified algorithms of signals processing, but the same ISA interface card, restricting its operation by the desktops with ISA bus and by Windows 95/98/ME.

Fig.4a. Gauge VD-1	Fig.4b. Gauge VD-2	Fig.4c. Gauge VD-3M

On the base of VD-2 signals acquisition through the Line IN input of the standard sound card the PC-based device “Spectra Recorder” (fig.6) was built, realizing the method of measurement of frequency dependencies of impedance characteristics.

Fig.5. Viscoelastograph VEM-2	Fig.6. Spectra Recorder

The modern PC-based devices of the third generation for the “Temporal Dynamics Recording of Mechanical Impedance and Dynamic Stiffness” (fig.7) and for the “Spectra Recording of Mechanical Impedance and Dynamic Stiffness” (fig.8) use the gauge VD-3M (fig.4c) and USB or Line IN interfaces, providing their operation on portable computers in any Windows.

Fig.7. Viscoelastograph “TDR MIDS”	Fig.8. Spectra Recorder “SpR MIDS”

The measurements by the devices of the first generation were performed by direct placing the gauge on the horizontal tissue surface and the pressure batching by the gauge weight. The measurements by the devices of the second generation were performed when the pressure batching was realized by the external mechanical devices – spring-based (Fig.5.) or lever-based (Fig.6.). The essential advantage of the third generation devices is availability of electronic system for pressure batching of the gauge to tissue, providing possibility of the stable measurements by the hand-held gauge.