An insight into electrical resistivity of white matter and brain tumors.

BACKGROUND: There is a lack of information regarding electrical properties of white matter and brain tumors. OBJECTIVE: To investigate the feasibility of in-vivo measurement of electrical resistivity during brain surgery and establish a better understanding of the resistivity patterns of brain tumors in correlation to the white matter. METHODS: A bipolar probe was used to measure electrical resistivity during surgery in a prospective cohort of patients with brain tumors. For impedance measurement, the probe applied a constant current of 0.7 µA with a frequency of 140 Hz. The measurement was performed in the white matter within and outside peritumoral edema as well as in non-enhancing, enhancing and necrotic tumor areas. Resistivity values expressed in ohmmeter (Ω∗m) were compared between different intracranial tissues and brain tumors. RESULTS: Ninety-two patients (gliomas WHO II:16, WHO III:10, WHO IV:33, metastasis:33) were included. White matter outside peritumoral edema had higher resistivity values (13.3 ± 1.7 Ω∗m) than within peritumoral edema (8.5 ± 1.6 Ω∗m), and both had higher values than brain tumors including non-enhancing (WHO II:6.4 ± 1.3 Ω∗m, WHO III:6.3 ± 0.9 Ω∗m), enhancing (WHO IV:5 ± 1 Ω∗m, metastasis:5.4 ± 1.3 Ω∗m) and necrotic tumor areas (WHO IV:3.9 ± 1.1 Ω∗m, metastasis:4.3 ± 1.3 Ω∗m), p=<0.001. No difference was found between low-grade and anaplastic gliomas, p = 0.808, while resistivity values in both were higher than the highest values found in glioblastomas, p = 0.003 and p = 0.004, respectively. CONCLUSIONS: The technique we applied enabled us to measure electrical resistivity of white matter and brain tumors in-vivo presumably with a significant effect with regard to dielectric polarization. Our results suggest that there are significant differences within different areas and subtypes of brain tumors and that white matter exhibits higher electrical resistivity than brain tumors.

Electrical impedance tomography is able to track changes in respiratory function in endotoxin-challenged rodents.

BACKGROUND AND OBJECTIVE: In order to assess and optimize the effect of new therapies for acute lung injury (ALI) in rodent models, a monitoring technique that continuously assesses the functional state of the lung is mandatory. Electrical impedance tomography (EIT) has been suggested as a technique for quantifying lung inflammation in ALI. However, EIT has not been evaluated in a rodent model of ALI. METHODS: EIT measurements were compared in ventilated Sprague-Dawley rats (n = 14), randomly subjected to intratracheal administration of endotoxin (LPS) or saline (control). Lung mechanics, lung weight wet/dry ratio and inflammatory markers in bronchoalveolar lavage fluid were also evaluated. RESULTS: LPS caused a significant decrease in lung compliance and TLC as compared with control (-42.0%, P = 0.04, and -27.9%, P = 0.02, respectively). These changes were paralleled by differences in mean impedance changes as detected by EIT (Spearman's rank correlation coefficient: rho = 0.66 and 0.73, respectively, P < 0.01). LPS increased the lung weight wet/dry ratio (6.35 +/- 0.42 vs 5.15 +/- 0.07, P = 0.003), and the bronchoalveolar lavage total WCC (8.96 +/- 1.87 vs 1.16 +/- 0.10 x 10(9)/L, P = 0.002) as compared with control. The lung weight wet/dry ratio was inversely related to the mean impedance change (rho = -0.76, P < 0.01). CONCLUSIONS: This study has demonstrated for the first time that eight-electrode EIT readily tracks the inflammatory response of lung tissue in a rodent model of ALI. EIT may thus provide a promising, non-invasive technique for monitoring the time-course of ALI in rodent models, and for testing novel pharmacological strategies to counter it.