Dielectric spectrogram for instantaneous evaluation of ischemic injury of the liver

Electrical properties of tissues sensitively reflect structural and physiologic changes. The authors examined the use of a dielectric spectrogram for instantaneous evaluation of ischemic injury of the liver. Wistar rats, which had enough collateral circulation for portal bypass with subcutaneous transposition of the spleen, were used. Four ischemic periods (15, 30, 60, and 120 min) were examined and followed by reflow. Permittivity and conductivity were measured at 39 frequency points in the 20 Hz-1 MHz range using an LCR meter system. They were then expressed in a loss tangent (LT) plot to clear their behavior. The maximum LT value (max-LT) and the minimum LT value (min-LT) of the normal liver were 3.98 ± 0.28 and 2.98 ± 0.22, and appeared in 15-20 kHz and 150-300 kHz, respectively. During the first 30 min after ischemia, max-LT decreased to 3.25 ± 0.14 (p < 0.005) and its range shifted to 0.3-0.6 kHz, and min-LT decreased to 1.35 ± 0.06 (p < 0.001) without shifting of range. Max-LT then decreased gradually and min-LT began to increase. After reflow, max-LT increased and higher max-LT was observed in the longer ischemic cases. Max-LT at 1 hr after reflow correlated negatively with recovery rate of bile flow at that time (y = -0.238x + 1.84, r² = 0.82). Additionally, the difference between max-LT and min-LT at just before reflow (dif-LT) showed a significant correlation coefficient with recovery rate of bile flow at 1 hr after reflow (y = 2.22x - 3.32, r² = 0.92).