In vivo electrical impedance spectroscopic monitoring of the progression of radiation-induced tissue injury

This study evaluates the potential of electrical impedance spectroscopy (EI S) as a noninvasive technique for tracking the progression of radiation-ind uced damage in normal muscle tissue. Male Sprague-Dawley rats were irradiat ed locally to the gastrocnemius and biceps femoris muscle, Single doses wer e administered using a procedure that spares skin and bone. Complex impedan ce spectral measurements (taken at 50 frequency points between 1 kHz and 1 MHz) were made at monthly intervals using recessed disk electrodes applied to the skin. A histological scoring scheme was developed for evaluation of injury. A strong dose-dependent progression of injury evident in both spect ral measurements and histological scoring has been observed. Latent time al so appears to be dependent on dose with changes induced by 70 Gy evident by 2 months, changes induced by 90 Gy observed by 1 month, and dramatic chang es found within 3 weeks at 150 Gy, Injury was morphologically comparable to the type of damage that occurs in response to small, fractionated doses, b ut on a much shorter time scale. Increased spectral shift was a consistent indicator of the extent of tissue injury at the time of measurement, The us e of a targe single dose resulted in an excellent model in terms of inducin g a significant progression in tissue injury over a short post-treatment fo llow-up period in the muscle mass while also providing a consistent locatio n for ill vivo electrical impedance measurements. The results show that EIS can follow radiation-induced tissue change, suggesting that EIS has the po tential to monitor the types of injury observed in late radiation damage of muscle tissue noninvasively. (C) 1999 by Radiation Research Society.