The detection of brain ischaemia in rats by inductive phase shift spectroscopy

Abstract

Ischaemia in the brain is an important clinical problem that is often monitored and studied with expensive devices such as MRI and PET, which are not readily available in low economical resource parts of the world. We have developed a new less expensive tool for non-invasive monitoring of ischaemia in the brain. This is a first feasibility study describing the concept. The system is based on the hypothesis that electromagnetic properties of the tissue change during ischaemia and that measuring the electromagnetic properties of the bulk of the brain with non-contact means can detect these changes. The apparatus we have built and whose design we describe here consists of two electromagnetic coils placed around the head. The system measures the bulk change in time of the phase difference between the electromagnetic signal on the two coils in a range of frequencies. A mathematical model simulating the device and the measurement is also introduced. Ischaemia was induced in the brain of rats by occlusion of the right cerebral and carotid arteries. Experimental subjects were monitored for 24 h. Inductive phase shift measurements were made at five frequencies in the range of 0.1-50 MHz eight times during the observation period. An ex vivo estimation of the percentage of necrosis in the ischemic subjects at t = 24 h was done. The mathematical model was also applied to the experimental tested situation. The results of both experiments and theory show significant phase shifts increase as a function of frequency and ischaemia time. The theoretical and experimental results suggest that the tested technique has the potential to detect the processes and level of ischaemia in the brain by non-invasive, continuous, bulk volumetric monitoring with a simple and inexpensive apparatus.

Detection of acute cerebral hemorrhage in rabbits by magnetic induction

“…Both the ICP and the MIPS increased with the bleeding volume, and a change in the MIPS suggested a change in the ICP because the latter was directly proportional to the MIPS. A change in the MIPS might reflect changes in the cerebrospinal fluid and cerebral blood volumes, as reported previously in the literature (13). Our MIPS system is a non-invasive, non-contact method for detection of the volume of cerebral hemorrhage.…”

“…Because the phase change of current in the excitation coil was affected by the magnetic field induced by the cylinder, the phase in the excitation coil θ Ve could be estimated from the following expression (13)where Z L represents the impedance of the excitation coil and Z out is the output impedance of the excitation source. The total phase shift between the voltages in the excitation and detection coils is given by the expression …”

“…The complex electrical properties of impaired tissue are substantially different from those of normal tissue, and various non-contact systems based on electromagnetic measurements have been proposed for different medical applications (9,10). Magnetic induction tomography has been studied as a potential tool for the non-invasive detection of edema (9-12) in addition to other non-contact approaches for detecting electromagnetic changes in tissue (13). Measuring changes in the electromagnetic properties of tissue with two non-contacting induction coils placed near the tissue have been proposed as an alternative method to detect clinical changes in the tissue (14,15).…”

“…Although the information thus obtained is not in the form of an image, it can provide temporal and even gross information about local changes in tissue (16) from non-contact, volume measurements. In particular, a change in the MIPS following the occurrence of a suspected clinical episode could serve as a first-order clinical warning by detecting the presence and progression of changes in tissue (13). In previous research, we carried out experimental studies to simulate the detection of cerebral edema by using a magnetic induction method, a single detection system, and a physical model of cerebral edema (17,18).…”

Twenty-Four-Hour Real-Time Continuous Monitoring of Cerebral Edema in Rabbits Based on a Noninvasive and Noncontact System of Magnetic Induction

“…Although the sensitivity was somewhat improved, the desired result was not achieved. The volumetric induction phase-shift spectroscopy (VIPS) method presented by Gonzalez et al [20] is self-referencing and can be performed in a short time, providing instantaneous information. As reported in 2013, VIPS data can be used for diagnosis to detect brain damage and even distinguish patients with edema from those with hematoma [21].…”