In vivo electrical properties of the healthy liver and the hepatic tumor in a mouse model between 1 Hz and 1 MHz during a thermal treatment.

Objective: Understansding the changing patterns of in vivo electrical properties for the target tissue is crucial for the accurate temperature monitoring and the treatment efficacy in thermal therapy. Our research aims to investigate the changing patterns and the reversibility of in vivo electrical properties for both healthy livers and liver tumors in a mouse model over a frequency range of 1 Hz to 1 MHz at temperatures between 30 °C to 90 °C.Methods and materials: The mice were anesthetized and the target organ was exposed. An 808-nm near-infrared laser was employed as the heating source to heat the organ in vivo. The four-needle electrode, connected to an impedance analyzer, was utilized to obtain the impedance at varying temperatures, which were monitored by a thermocouple.Results: The findings indicated a gradual decline in impedance with an increase in temperature. Furthermore, the impedance was normalized to that at 30 °C, and the real part of the normalized impedance was defined as the k-values, which range from 0 to 1. The results demonstrated a linear correlation between k-values and temperatures (R2 > 0.9 for livers and R2 > 0.8 for tumors). Significant differences were observed between livers and tumors at 1, 10 and 50 kHz (p < 0.05). Additionally, it was demonstrated that the electrical properties could be reversed when the temperature was below or equal to 45 °C.Conclusion: We believe that these results will contribute to the advancement of radiofrequency ablation systems and the development of techniques for temperature monitoring during liver thermal treatment.

A preliminary study on the application of electrical impedance tomography based on cerebral perfusion monitoring to intracranial pressure changes.

Background: In intracranial pathologic conditions of intracranial pressure (ICP) disturbance or hemodynamic instability, maintaining appropriate ICP may reduce the risk of ischemic brain injury. The change of ICP is often accompanied by the change of intracranial blood status. As a non-invasive functional imaging technique, the sensitivity of electrical impedance tomography (EIT) to cerebral hemodynamic changes has been preliminarily confirmed. However, no team has conducted a feasibility study on the dynamic detection of ICP by EIT technology from the perspective of non-invasive whole-brain blood perfusion monitoring. In this study, human brain EIT image sequence was obtained by in vivo measurement, from which a variety of indicators that can reflect the tidal changes of the whole brain impedance were extracted, in order to establish a new method for non-invasive monitoring of ICP changes from the level of cerebral blood perfusion monitoring. Methods: Valsalva maneuver (VM) was used to temporarily change the cerebral blood perfusion status of volunteers. The electrical impedance information of the brain during this process was continuously monitored by EIT device and real-time imaging was performed, and the hemodynamic indexes of bilateral middle cerebral arteries were monitored by transcranial Doppler (TCD). The changes in monitoring information obtained by the two techniques were compared and observed. Results: The EIT imaging results indicated that the image sequence showed obvious tidal changes with the heart beating. Perfusion indicators of vascular pulsation obtained from EIT images decreased significantly during the stabilization phase of the intervention (PAC: 242.94 ± 100.83, p < 0.01); perfusion index which reflects vascular resistance increased significantly in the stable stage of intervention (PDT: 79.72 ± 18.23, p < 0.001). After the intervention, the parameters gradually returned to the baseline level before compression. The changes of EIT indexes in the whole process are consistent with the changes of middle cerebral artery velocity related indexes shown in TCD results. Conclusion: The EIT image combined with the blood perfusion index proposed in this paper can reflect the decrease of cerebral blood flow under the condition of increased ICP in real time and intuitively. With the advantages of high time resolution and high sensitivity, EIT provides a new idea for non-invasive bedside measurement of ICP.