NONINVASIVE, IN-VIVO ELECTRICAL-IMPEDANCE OF EMT-6 TUMORS DURING HYPERTHERMIA - CORRELATION WITH MORPHOLOGY AND TUMOR-GROWTH-DELAY

The electrical impedance at frequencies from 100Hz to 40MHz of EMT-6 t umours was measured non-invasively, in vivo, during hyperthermia using an apparatus constructed for this purpose. Histology and morphometry were performed on tumours harvested periodically during the heating. A ratio of conductivities at two frequencies (sigma(10MHz)/sigma(10KHz) ), which minimizes the tissue temperature-coefficient effects, was use d to correlate impedance changes with the histopathological changes. T he bulk of the cell population followed a necrotic cell death sequence during the heating. Initial increase of the sigma-ratio correlated wi th cell swelling, and a reversal of the rate of this increase correlat ed with the appearance of small membrane breaks and evidence of mitoch ondrial damage. A continued, slowing sigma-ratio increase to a maximum correlated with continued cell swelling accompanied by increasing mem brane disruption. The subsequent decrease in sigma-ratio correlated wi th continued general cell lysing. Between the appearance of the first membrane breaks (sigma-ratio rate peak) and the evidence of general ly sing (sigma-ratio peak), the tumour-growth-delay increased non-linearl y. Because the sigma-ratio consistently discerned these events, these measurements were able to predict the fate of this cell population whe n subjected to hyperthermia. Knowledge of temperature or time of heati ng was not required.