Detection Technique And Preliminary Experimental Study On Bioimpedance Of The Intracranial Hematoma And Edema

Cerebral infarct, intracranial hematoma and edema are deadly diseases, which can cause high deformity and death rate. Better prognosis can be induced by early detection and treatment. But at present, no such monitoring technique or device is available for detecting the intracranial pathological changes early and non-invasively.The former researchers had indicated that the bioimpedance of intracranial issues may be changed by intracranial diseases. And there are high research worthiness and application potential of using bioimpedance technique to detect intracranial diseases. But, the resistivity of skull is much higher than that of the brain and scalp, and only weak impedance change can be detected non-invasively. So it is difficult to detect intracranial impedance change non-invasively.Based on the analysis of the latest research works in recent years, aimed at the demand of early detection of the intracranial pathological changes and the key problems in brain non-invasive bioimpedance technique research works, for the need and actuality of our research group, this paper mainly fulfilled following research works.1. Aimed at the bilateral bioimpedance measurement of brain, two electrode placement schemes are designed and simulated. There are six electrodes used in the first scheme. The drive electrodes are placed on the midline, the bilateral measurement electrodes are placed symmetrically and respectively on the left and right side of the midline. There are four electrodes used in the second scheme. The bilateral electrodes are placed symmetrically and respectively on either side of head. The electrodes acted as the drive and measurement electrode synchronously. The simulation result showed that the first scheme is more sensitive in detecting impedance change in the measurement region. And because of the using of tetrapolar measurement, the impact of interface impedance between electrode and skin can be reduced. So the first scheme is adopted in this study to detect bilateral impedance of head.2. Based on the tetrapolar measurement method, a high performance, double measurement channels and multi-frequency impedance measurement system was designed. The following features were implemented in this system:1) With its two measurement channels, bilateral bioimpedance of brain can be measured.2) The direct digital frequency synthesis technique is used to design stimulation source. The orthogonal sequential demodulation method is used to demodulate bioimpedance information.3) The frequency of stimulation source can be selected in the range of 5 ~ 300 kHz. The drive current can be selected in a range of 0 ~ 1mA.4) In the full range of working frequencies, the CMRR of this system is higher than 80dB.5) As all the system is integrated in one box, it is easy to move the system or use it in clinical monitor. Along with its special application software, this system has strong practicability.3. With this bioimpedance measurement system, two animal experiments were done using rabbit as the experiment animal.1) Experiment on intracranial hematoma animal modelBilateral non-invasive cerebral impedance was measured using scalp electrode by the system. Intracranial hematoma animal model was induced by injecting self blood. Impedance change was observed in the experiment. The result showed that the impedance of"injecting side"rose about 0.91%, while that of"opposite side"rose about 0.45%.2) Experiment on cerebral edema animal modelBilateral non-invasive cerebral impedance was measured using scalp electrode by the system. Intracranial hematoma animal model was induced by photochemical induction method. Impedance change was observed while cerebral infarct and the following cerebral edema course. The impedance began to rise 15 minute after turning on the light. The light was kept for 30 minutes. The impedance raised about 1.5% when the light was turned off. The impedance kept rising after light off, and another 90 minute later, a total increase of about 4% of the original impedance was found. Impedance of the opposite side also raised about half of that of operated side.The first experiment proved that intracranial impedance changes can be measured non-invasively using scalp electrode. The intracranial hematoma and edema experiments indicated that cerebral impedance may rise while there is a cerebral pathological change. It is possible to detect cerebral pathological change using non-invasive bioimpedance technology. 4. Preliminary experiment on healthy human brain impedance monitoring was implemented using this impedance measurement system. It was proved by experiments that the brain impedance changes could be detected by this measurement system. As healthy human does not have intracranial hematoma and edema, it was not observed directly that the impedance change caused by intracranial hematoma and edema. But, impedance changes, caused by heartbeat and deep inspiration, could be measured by this system.The main innovations of this paper include the following points:Simulation study on electrodes configuration was performed. An electrodes configuration, which is suitable for brain impedance measurement, was presented.Based on the tetrapolar measurement method, aimed at the need of intracranial hematoma and edema monitoring, a high performance, double measurement channels and multi-frequency impedance measurement system was designed. A dynamic adjustment method of analog gain and a calibration method of impedance measurement result were put forward.Based on the simulation study, two data analysis parameters were presented. It was proved by the animal experiments that intracranial hematoma and edema could be these parameters evaluated by these two indexes and proper standard.In this paper, based on simulation study, a suitable electrodes configuration and two data analysis indexes were presented. Based on the tetrapolar measurement method, aimed at the need of intracranial hematoma and edema monitoring, a high performance, double measurement channels and multi-frequency impedance measurement system was designed. It was proved by the animal model experiments that impedance changes, caused by intracranial hematoma and edema, can be measured non-invasively by the system we developed. In the health human experiments, impedance fluctuations caused by heartbeat and deep inspiration were observed. So the non-invasive impedance measurement technique can also be used in the impedance measurement on the human head. The works in this paper have made a foundation for using non-invasive bioimpedance technique to monitor cerebral pathological changes.