gms | German Medical Science

Objective: Reported brain tissue resistivity to date is usually obtained from sample investigation in vitro. There is also a lack of information regarding conductivity of brain tumors. This is a pilot study to investigate the feasibility of a new technique to perform an in-vivo measurement of electrical resistivity of intracranial tissue and brain tumors.

Methods: Patients who were admitted at our institute between November 2017 and August 2019 for operative treatment of brain tumor were screened for the study. Intraoperative measurement of tissue resistivity was performed using a bipolar probe with a defined distance between the two poles applying an alternating current of 0.7 µA with a frequency of 140 Hz. The measurement was conducted on the dura, cortex and the exposed solid tumor tissue subsequently as well as white matter when possible. Impedance values were expressed in ohm (Ω). Resistivity values expressed in Ω.m were extrapolated through calibration of the measurement device and calculation of the geometrical factor of the measurement probe. Resistivity values were compared between different intracranial tissues and brain tumors.

Results: Eighty-one patients were included in the study. Median of resistivity values of the dura was 15.9 Ω.m (5.51-34.6), brain cortex 10.01 Ω.m (3.78-23.17), white matter 12.75 Ω.m (11.2-15.14), peritumoral edema 8.39 Ω.m (6.7-10.08) and tumor 5.01 Ω.m (1.64-10.64). Values of dura were the highest followed by white matter, cortex, peritumoral edema and tumor, p<0.001. Mean of resistivity values of WHO grade II tumors was 6.75±2.12 Ω.m, WHO grade III tumors 6.76±1.42 Ω.m, WHO grade IV tumors 4.44±1.41 Ω.m and metastases 4.99±1.57 Ω.m. The measurement made at different three points within the tumors showed significant differences, p<0.05. Resistivity values of metastases were similar to those of glioblasoma , p=0.199. Values of glioblastoma were higher than those of anaplastic and low grade glioma, p<0.001, while the difference between anaplastic and low grade gliomas was not significant, P=0.993.

Conclusion: The new technique enables in-vivo measurement of electrical resistivity of brain tissue and brain tumors with reproducible results and without damaging brain tissue. First results showed significant differences in tissue resistivity between brain tumors and white matter as well as between different subtypes of brain tumors. Further studies will be necessary to investigate the clinical application of the new technique.