In vivo bioimpedance changes during haemorrhagic and ischaemic stroke in rats: Towards 3D stroke imaging using electrical impedance tomography

Electrical impedance tomography (EIT) could be used as a portable non-invasive means to image the development of ischaemic stroke or haemorrhage. The purpose of this study was to examine if this was possible using time difference imaging, in the anesthetised rat using 40 spring-loaded scalp electrodes with applied constant currents of 50-150 μA at 2 kHz. Impedance changes in the largest 10% of electrode combinations were -12.8% ± 12.0% over the first 10 min for haemorrhage and +46.1% ± 37.2% over one hour for ischaemic stroke (mean ± SD, n = 7 in each group). The volume of the pathologies, assessed by tissue section and histology post-mortem, was 12.6 μl ± 17.6 μl and 12.6 μl ± 17.6 μl for haemorrhage and ischaemia respectively. In time difference EIT images, there was a correspondence with the pathology in 3/7 cases of haemorrhage and none of the ischaemic strokes. Although the net impedance changes were physiologically reasonable and consistent with expectations from the literature, it was disappointing that it was not possible to obtain reliable EIT images. The reason for this are not clear, but probably include confounding effects of secondary ischaemia for haemorrhage and tissue and cerebrospinal fluid shifts for the stroke model. With this method, it does not appear that EIT with scalp electrodes is yet ready for clinical use

Exploratory Study on the Methodology of Fast Imaging of Unilateral Stroke Lesions by Electrical Impedance Asymmetry in Human Heads

Stroke has a high mortality and disability rate and should be rapidly diagnosed to improve prognosis. Diagnosing stroke is not a problem for hospitals with CT, MRI, and other imaging devices but is difficult for community hospitals without these devices. Based on the mechanism that the electrical impedance of the two hemispheres of a normal human head is basically symmetrical and a stroke can alter this symmetry, a fast electrical impedance imaging method called symmetrical electrical impedance tomography (SEIT) is proposed. In this technique, electrical impedance tomography (EIT) data measured from the undamaged craniocerebral hemisphere (CCH) is regarded as reference data for the remaining EIT data measured from the other CCH for difference imaging to identify the differences in resistivity distribution between the two CCHs. The results of SEIT imaging based on simulation data from the 2D human head finite element model and that from the physical phantom of human head verified this method in detection of unilateral stroke

A bioimpedance-based monitor for real-time detection and identification of secondary brain injury

Secondary brain injury impacts patient prognosis and can lead to long-term morbidity and mortality in cases of trauma. Continuous monitoring of secondary injury in acute clinical settings is primarily limited to intracranial pressure (ICP); however, ICP is unable to identify essential underlying etiologies of injury needed to guide treatment (e.g. immediate surgical intervention vs medical management). Here we show that a novel intracranial bioimpedance monitor (BIM) can detect onset of secondary injury, differentiate focal (e.g. hemorrhage) from global (e.g. edema) events, identify underlying etiology and provide localization of an intracranial mass effect. We found in an in vivo porcine model that the BIM detected changes in intracranial volume down to 0.38 mL, differentiated high impedance (e.g. ischemic) from low impedance (e.g. hemorrhagic) injuries (p \u3c 0.001), separated focal from global events (p \u3c 0.001) and provided coarse ‘imaging’ through localization of the mass effect. This work presents for the first time the full design, development, characterization and successful implementation of an intracranial bioimpedance monitor. This BIM technology could be further translated to clinical pathologies including but not limited to traumatic brain injury, intracerebral hemorrhage, stroke, hydrocephalus and post-surgical monitoring

Modeling Brain Using Parameters of Passive Electrical Circuits

Brain is the central and most complex organ in the human body. It controls most of the body functions, processing, integrating, and coordinating the information it receives from the organs, and sending decision instructions to the rest of the body. Brain injury may occur due to external environmental and/or internal influences. Timely diagnosing and differentiating the type of brain injury is critical. CT and MRI are often used for the diagnosis, which may not be available at a remote location or at an accident site or an emergency vehicle. This thesis contributes to the modeling of the brain from the electrical point of view, considering the structural complexity of the head composed of biological tissues with different dielectric properties. The goal of the thesis is to develop electrical models of the brain using parameters of passive electrical circuits. The models are developed for a normal brain and a brain with pathological conditions such as edema (swelling) and hemorrhage (bleeding). The circuit models are simulated at a range of frequencies from 1 Hz to 200 kHz. The experiment data is collected on a sheep brain surrounded by phantom tissue using bioimpedance analyzer at a range of frequencies from 1 Hz to 200 kHz. The simulation results are compared with experiment data

In vitro localization of intracranial haematoma using electrical impedance tomography semi-array

Electrical Impedance Tomography is a non-invasive and portable method that has good potential as an ‎alternative to the conventional modalities for early detection of intracranial haematomas in high risk patients. ‎Early diagnosis can reduce treatment delays and most significantly can impact patient outcomes. Two eight-‎electrode layouts, a standard ring full array (FA) and a semi-array (SA), were investigated for their ability to ‎detect, localise and quantify simulated intracranial haematomas in vitro on ovine models for the purpose of ‎early diagnosis. SA layout speeds up electrode application and avoids the need to move and lift the patient's ‎head. Haematomas were simulated using gel samples with the same conductivity as blood. Both layouts, FA ‎and SA, could detect the presence of haematomas at any location within the skull. The mean of the relative ‎radial position error with respect to the brain radius was 7% for FA and 6% for SA, for haematomas close to the ‎electrodes, and 11% for SA for haematomas far from the electrodes at the back of the head. Size estimation ‎was not as good; the worst size estimation error for FA being around 30% while the best for SA was 50% for ‎simulated haematomas close to the electrodes.

Clinical Applications of Electrical Impedance Tomography in Stroke and Traumatic Brain Injury

Electrical Impedance Tomography (EIT) is a medical imaging technology which uses voltage measurements on the boundaries to reconstruct internal conductivity changes. When applied to imaging brain function, EIT is challenged by the unique geometry of the head and the high variability in the conductivities of brain tissue. Stroke and Trau-matic Brain Injury (TBI) are two of the leading causes of death and long-term disability worldwide. It has been suggested that EIT, which is already in clinical use primarily as a means of assessing lung function, could be used as a pre-hospital diagnostic tool for stroke and TBI, and for bedside monitoring for brain injury patients. The main aim of this PhD thesis is to bring the application of EIT in brain injury closer to regular clinical use. Chapter 1 introduces the concepts of EIT, stroke and TBI, and provides a comprehensive review of clinically relevant neuroimaging techniques and the current state of brain EIT. Chapter 2 presents the results of a series of lab experiments designed to investigate the characteristics and mechanisms of drift in measured boundary voltages, which is the key technical barrier to brain monitoring with EIT. Ex-periments were conducted on lab phantoms, vegetable skin, and healthy human subjects. Chapter 3 describes a feasibility study of monitoring for brain injury with EIT over several hours, using noise recorded on real healthy volunteers. This study also compares the performance of different electrode types. Chapter 4 presents a clinical pilot study performed on acute stroke patients. Multi-frequency (MF) EIT data were record-ed on patients and healthy controls to create the first of its kind clinical EIT dataset to be used as a resource for future research for the EIT community. Finally, the ability to identify stroke patients is demonstrated on the clinical EIT dataset

Zeffiro user interface for electromagnetic brain imaging: a GPU accelerated FEM tool for forward and inverse computations in Matlab

This article introduces the Zeffiro interface (ZI) version 2.2 for brain imaging. ZI aims to provide a simple, accessible and multimodal open source platform for finite element method (FEM) based and graphics processing unit (GPU) accelerated forward and inverse computations in the Matlab environment. It allows one to (1) generate a given multi-compartment head model, (2) to evaluate a lead field matrix as well as (3) to invert and analyze a given set of measurements. GPU acceleration is applied in each of the processing stages (1)-(3). In its current configuration, ZI includes forward solvers for electro-/magnetoencephalography (EEG) and linearized electrical impedance tomography (EIT) as well as a set of inverse solvers based on the hierarchical Bayesian model (HBM). We report the results of EEG and EIT inversion tests performed with real and synthetic data, respectively, and demonstrate numerically how the inversion parameters affect the EEG inversion outcome in HBM. The GPU acceleration was found to be essential in the generation of the FE mesh and the LF matrix in order to achieve a reasonable computing time. The code package can be extended in the future based on the directions given in this article

Electrical Impedance Tomography: From the Traditional Design to the Novel Frontier of Wearables

Electrical impedance tomography (EIT) is a medical imaging technique based on the injection of a current or voltage pattern through electrodes on the skin of the patient, and on the reconstruction of the internal conductivity distribution from the voltages collected by the electrodes. Compared to other imaging techniques, EIT shows significant advantages: it does not use ionizing radiation, is non-invasive and is characterized by high temporal resolution. Moreover, its low cost and high portability make it suitable for real-time, bedside monitoring. However, EIT is also characterized by some technical limitations that cause poor spatial resolution. The possibility to design wearable devices based on EIT has recently given a boost to this technology. In this paper we reviewed EIT physical principles, hardware design and major clinical applications, from the classical to a wearable setup. A wireless and wearable EIT system seems a promising frontier of this technology, as it can both facilitate making clinical measurements and open novel scenarios to EIT systems, such as home monitoring