An insight into electrical resistivity of white matter and brain tumors

Surgical identification of brain tumour margins through impedance monitoring and electrocorticography and the potential for their combined use: A systematic review

CONTEXT

Primary central nervous system tumours have poor survival outcomes. Surgery, the first-line treatment, presents technical limitations, such as visualising the whole tumour border. Intracranial impedance monitoring and electrocorticography techniques provide insights into the local field potential characteristics, resistance and capacitance properties of brain tissue. We hypothesised that measurements obtained by either modality can distinguish between tumour and healthy brain tissue intraoperatively.

METHODS

A "Preferred Reporting Items for Systematic Reviews and Meta-Analyses" (PRISMA)-compliant systematic review was conducted, searching PubMed, Ovid, Scopus, Cochrane and Web of Science. Studies on electrocorticography and impedance monitoring in patients with brain tumours were included. Data on patient demographics, technical details, obtained results and safety were extracted and analysed in Excel.

RESULTS

Eighteen studies involving 286 patients in total were identified. Ten impedance studies showed that brain tumour tissue has significantly different values than healthy tissue, while its resistivity varies, being either higher or lower. Eight electrocorticography studies indicated increased high gamma power and altered connectivity in tumour tissue. No studies integrated impedance monitoring and electrocorticography in one device.

CONCLUSION

Impedance and electrocorticography measurements have the potential of differentiating between tumour and unaffected issues intra-operatively. Larger studies with standardised protocols are needed to validate these findings. Additionally, the combination of these two modalities has the potential for improved specificity with a single device. Future research should explore the role of these modalities in enhancing tumour margin identification across different tumour subtypes and in improving survival outcomes.

Temperature and Frequency Dependence of Human Cerebrospinal Fluid Dielectric Parameters

Accurate human cerebrospinal fluid (CSF) dielectric parameters are critical for biological electromagnetic applications such as the electromagnetic field modelling of the human brain, the localization and intensity assessment of electrical generators in the brain, and electromagnetic protection. To detect brain damage signals during temperature changes by electrical impedance tomography (EIT), the change in CSF dielectric parameters with frequency (10 Hz-100 MHz) and temperature (17-39 °C) was investigated. A Debye model was first established to capture the complex impedance frequency and temperature characteristics. Furthermore, the receiver operating characteristic (ROC) analysis based on the dielectric parameters of normal and diseased CSF was carried out to identify lesions. The Debye model's characteristic fc parameters linearly increased with increasing temperature (R2 = 0.989), and R0 and R1 linearly decreased (R2 = 0.990). The final established formula can calculate the complex impedivity of CSF with a maximum fitting error of 3.79%. Furthermore, the ROC based on the real part of impedivity at 10 Hz and 17 °C yielded an area under the curve (AUC) of 0.898 with a specificity of 0.889 and a sensitivity of 0.944. These findings are expected to facilitate the application of electromagnetic technology, such as disease diagnosis, specific absorption rate calculation, and biosensor design.

Transcranial MEPs predict clinical outcome during minimally invasive dorsal decompression for cervical spondylotic myelopathy

OBJECTIVES

Motor evoked potential (MEP) monitoring is a reliable method for real-time assessment of corticospinal tract integrity. However, the potential benefits of MEP monitoring during degenerative spine surgery remain controversial. This study aims to determine the role of MEP monitoring during surgery for cervical spondylotic myelopathy (CSM) in prediction of prognosis.

METHODS

Transcranial electrical stimulation was performed to elicit MEPs during dorsal decompression for the treatment of CSM. MEP-threshold levels were assessed separately at the beginning and end of the surgery in upper extremity muscles corresponding to nerve roots at the level of/distal to the decompression site. Clinical outcome was measured using the modified Japanese Orthopedic Association score (mJOA).

RESULTS

The study included 47 patients. 31 patients (66 %) showed improvements in neurological function at discharge. A measurable improvement in the majority of tested muscles, or in at least one muscle group, in a given patient highly correlated with mJOA score increase at discharge (p < 0.001) with an odds ratio of 10.3 (CI:2.6-34.4) and 11.4 (CI:2.8-41.3), respectively. Conversely, MEP deterioration was not associated with worse clinical outcome, nor was it predictive of failure to recover.

CONCLUSION

MEP improvement during CSM surgery seems to be highly predictive of early postoperative neurological recovery and could indicate subclinically enhanced signal conduction. This highlights the potential of MEP monitoring as an intraoperative, real-time predictive tool for clinical recovery after decompression in patients with CSM.

A System-based Approach for the Evaluation of Electromechanical Properties of Brain Tumors

We have developed a semi-automated system integrated with MEMS-based electromechanical sensors to characterize human brain tumors. The electrical impedance and elastic moduli of three types of brain tumors and six normal brain regions were evaluated using the system. The impedance and elastic modulus of glioma was found to be significantly lower than the normal region. It was also observed that the white matter tissues had higher impedance and elastic moduli compared with the grey matter of the same neuroanatomic location. There were observable differences in the electromechanical behavior of gliomas, which originate from glial cells to that of schwannoma and meningioma of different cellular origins. Clinical Relevance- The observations suggest that simultaneous electromechanical characterization of brain tumors can serve as an effective tool for tumor delineation. The developed tool can be used alongside gold standard histopathological analysis to better understand human brain tumors.

Mini Review: Impedance Measurement in Neuroscience and Its Prospective Application in the Field of Surgical Neurooncology

Impedance measurement of human tissue can be performed either in vivo or ex vivo. The majority of the in-vivo approaches are non-invasive, and few are invasive. To date, there is no gold standard for impedance measurement of intracranial tissue. In addition, most of the techniques addressing this topic are still experimental and have not found their way into clinical practice. This review covers available impedance measurement approaches in the neuroscience in general and specifically addresses recent advances made in the application of impedance measurement in the field of surgical neurooncology. It will provide an understandable picture on impedance measurement and give an overview of limitations that currently hinders clinical application and require future technical and conceptual solutions.