Experimental Research Of Cerebral Blood Flow Detection Based On Magnetic Induction Phase Shift Technology

Cerebrovascular diseases are that all kinds of brain diseases caused by abnormalities of cerebral blood flow. It is seriously threatened human health and life, with high percent of incidence, recurrence, disability and mortality. It is also one cause of disability and death in the elderly major diseases. The number of worldwide people who have been died from cerebrovascular disease is about 4.6 million and it is the second leading reason of human death. Due to vigorous metabolism and complex physiological function, brain needs a large number of oxygen and has not reserve energy source, so it is strongly dependent on blood. When the cerebral blood flow was interrupted 1~30s, the brain cells would be damaged, it could be recovered. When the blood flow was interrupted 3~5min, the brain cells would be seriously damaged, and less could be able to recover normal. If the cerebral blood flow was interrupted constantly 30 min, then the brain cells would be severely necrosis and loss of function. Currently, there was no clinical methods and technique of real-time continuous monitoring cerebral blood flow. Therefore, the development of a real-time continuous monitoring of cerebral blood flow techniques is important and significant to the early prevention and diagnosis of cerebrovascular disease.Firstly, the paper studies the basic principles of magnetic induction phase shift and fundamental electromagnetic characteristics of cerebral blood flow. To overcome the shortcomings of existing equipments and methods of monitoring cerebral blood flow, we established a non-invasive and non-contact CBF measurement system based on magnetic induction phase shift technology. We applied an excited signal generated by a high phase stability generator to self-designed planar coil sensor, and the measured head was placed in the center of the sensor. Due to the exciting magnetic field from the exciting coil in the sensor, the periodically changing of CBF generated a disturbed magnetic field. It was received by receiving coil. The exciting and received signals were acquired by NI-PXI through data acquisition. Then phase shift data were calculated, stored and displayed by using Lab VIEW software in NI-PXI. Meanwhile,in order to calibrate the human heart condition, synchronous acquiring ECG signal. In the course of CBF signal processing, we used wavelet transform, high-pass filter and cubic spline interpolation method to remove baseline drift. The CBF signal after processing was preferable and propitious to feature extraction and statistical analysis.In order to clarify the physical meaning of detected signals by this system, a physical model experiment was carried out. A miniature pumps and a rubber tube were used to simulate heart and blood vessel. To further validate the feasibility and stability of this experimental system for cerebral blood flow measuring, phase shift data from 10 healthy volunteers were acquired. The data were processed and analyzed by using Wavelet analysis to remove the whole baseline drift, high-pass filter to remove the breathing interference, spectrum analysis and the Cubic Spline to remove the local baseline drift. The physical experiment result showed that the MIPS signal represented the diastolic and systolic of rubber tube. The volunteers experiment results showed that the MIPS signal represents cyclical changes in cerebral blood flow. By statistical analysis of the value of waveform area, we found that the second volunteer’s areas of experimental results are 0.0254 ± 0.0005266. It indicated the system is repeatability for the same subject. Meanwhile, by multiple comparisons between 10 volunteers’ areas of experimental results, we found that it have obvious differences between 10 volunteers’ experimental results.The experiment results show that the system can detect the changes of cerebral blood flow and has advantage of non-contact, high-precision, high sensitivity, continuous monitoring, etc. As a new method of cerebral blood flow detecting the magnetic induction phase shift has potential application value.