M. Itkis et al., THE SQUARE-WAVE APPROACH TO IMPEDANCE MEASUREMENT OF BRAIN-TISSUE WATER DYNAMICS, Journal of neuroscience methods, 59(2), 1995, pp. 237-244
Electrical properties of living soft tissue have been used to analyze
their structure and function. Presently, the 'admittance locus' method
, with the sine-wave signal of changing frequency, is the most informa
tive continuous method for analyzing extra- and intracellular water co
ntent in brain tissue. Using the square-wave signal in lieu of the sin
e-wave signal, we can avoid cumbersome and costly measurements and fac
ilitate real-time data processing. An isolation-calibration device was
developed for the present study in order to condition and stabilize e
lectrical current through the brain cortex. This device was also used
for impedance calibration before and after the experiments. We propose
a simple algorithm for data analysis on the basis of equivalent circu
it approach, which allows to develop a computer program for data proce
ssing. Preliminary experiments on rat brains were carried out with a 0
.2-0.5 mm stainless-steel tetrapolar electrode system. These studies s
howed good linearity between stimulating currents (L = 5-30 mu A) thro
ugh the external electrodes in the brain cortex and a drop in voltage
which was measured by 2 inner electrodes. The results of the device an
d the program accuracy tests allow us to choose the optimal range for
the working current. We can recommend this method for usage in animal
experiments.