In electrical impedance tomography (EIT), it is difficult to obtain the intracranial impedance due to the highly resistive skull enclosing the brain. Therefore, a high-precision data acquisition system is required for brain EIT. In this paper, we used a high-precision digital synthesis method and a digital demodulation technique with high noise immunity to eliminate random errors. Moreover, we focused on two problems encountered during EIT data acquisition: 1) the shunt effect on the excitation current due to the distributed capacitance between electrodes and ground and 2) high common-mode voltages in the boundary measurements. We designed a new electrode interface to reduce the influence of the distributed capacitance and a programmable current source to accurately compensate for the excited current. We also proposed a new voltmeter circuit with improved CMRR. Overall, this EIT data acquisition system can produce a programmable current with SNR greater than 89 dB. It can also measure the voltage difference precisely with CMRR higher than 75 dB with a 1-kQ impedance imbalance. The results on a calibration model show that this system has a high SNR of 83 dB and a low reciprocity error of 0.125%. In addition, EIT imaging results were acquired using a brain physical phantom. The system can detect small disturbances of 0.35% in volume (1.99% of the cross-sectional area) and 17% in resistivity. Experiments on healthy volunteers also suggest that small intracranial impedance variations due to temporary occlusion and reperfusion of the unilateral carotid artery may be monitored by the system.

Variations of conductive fluid content in brain tissue (e.g. cerebral edema) change tissue impedance and can potentially be measured by Electrical Impedance Tomography (EIT), an emerging medical imaging technique. The objective of this work is to establish the feasibility of using EIT as an imaging tool for monitoring brain fluid content. a prospective study. In this study EIT was used, for the first time, to monitor variations in cerebral fluid content in a clinical model with patients undergoing clinical dehydration treatment. The EIT system was developed in house and its imaging sensitivity and spatial resolution were evaluated on a saline-filled tank. 23 patients with brain edema. The patients were continuously imaged by EIT for two hours after initiation of dehydration treatment using 0.5 g/kg intravenous infusion of mannitol for 20 minutes. Overall impedance across the brain increased significantly before and after mannitol dehydration treatment (p = 0.0027). Of the all 23 patients, 14 showed high-level impedance increase and maintained this around 4 hours after the dehydration treatment whereas the other 9 also showed great impedance gain during the treatment but it gradually decreased after the treatment. Further analysis of the regions of interest in the EIT images revealed that diseased regions, identified on corresponding CT images, showed significantly less impedance changes than normal regions during the monitoring period, indicating variations in different patients' responses to such treatment. EIT shows potential promise as an imaging tool for real-time and non-invasive monitoring of brain edema patients.

The dielectric properties of human liver were determined by characterization of tissue absorption and coupling of electromagnetic energy in the electromagnetic field. In this study the ex-vivo dielectric properties of human hepatocellular carcinoma (well and moderately differentiated), liver hemangioma, hepatic fibrosis (stages S1 and S2), and normal liver tissue were measured and analyzed over the frequency range of 10 Hz to 100 MHz. The dielectric properties over the frequency range can reflect tissue information including biological macromolecules, vesicles, and cellular membrane; these information aids in distinguishing different physiological states and lesions. The ex-vivo conductivity, permittivity, resistivity, as well as the characteristic parameters between the lesions and normal liver were analyzed and their differences were also verified. The data can contribute to developing bioelectric applications for tissue diagnostics and creating more accurate computer models for medical applications.

ACUTE AORTIC DISSECTION type A is a lethal disease, and its natural mortality rate within 48 hours is over 50%.¹ x 1 MéSzáRos, I.N., MóRocz, J.Z., SzláVi, J.Z. et al. Epidemiology and clinicopathology of aortic dissection. (Available at)Chest. 2000; 117: 1271–1278 https://doi.org/10.1378/chest.117.5.1271 Abstract | Full Text | Full Text PDF | PubMed | Scopus (531) | Google Scholar See all References Total aortic arch replacement (TAAR) under cardiopulmonary bypass (CPB) is one of the conventional surgical treatments. Although brain protection strategies such as hypothermic circulatory arrest (HCA) and selective antegrade cerebral perfusion have been used during TAAR, neurological dysfunction (ND) remains a common complication.² x 2 Hogue, C.W., Palin, C.A., and Arrowsmith, J.E. Cardiopulmonary bypass management and neurologic outcomes: An evidence-based appraisal of current practices. Anesth Analg. 2006; 103: 21–37 https://doi.org/10.1213/01.ANE.0000220035.82989.79 Crossref | PubMed | Scopus (171) | Google Scholar See all References A 2012 retrospective review of patients following a type A dissection showed transient ND in 33.6% and stroke in 16.4% of the 122 patients followed for 30 days after surgery.³ x 3 Haldenwang, P.L., Wahlers, T., Himmels, A. et al. Evaluation of risk factors for transient neurological dysfunction and adverse outcome after repair of acute type A aortic dissection in 122 consecutive patients. Eur J Cardiothorac Surg. 2012; 42: e115–e120 https://doi.org/10.1093/ejcts/ezs412 Crossref | PubMed | Scopus (21) | Google Scholar See all References