Study On Key Technology Of Cerebral Hemodynamics Detection Based On CWNIRS And ICG Densitometry

Brain is the largest oxygen-consuming neurophysiological organ,and its metabolism depends on the adequate oxygen supply from the blood circulation.O nce the blood and oxygen supply can not meet the compensation of the brain tissue microcirculation,the irreversible tissue damage to the neurons will be caused due to insufficient energy intaking.Specifically,the brain tissue consumes a lot of energy,b ut it barely has any oxygen reserve function,which makes a extremely low tolerability of cerebral ischemia-hypoxia injury.For now,cerebral hemodynamics parameters are taken as the diangnosis indexes of the local cerebrovascular circulation and the compensatory function in clinical practice.Cerebral hemodynamics parameters mainly include regional blood flow,blood flow velocity,perfusion pressure,oxygen saturation and others,which centre on the dynamic cerebral blood perfusion characteristics of brain tissue.Cerebral hemodynamics parameters are considered as the most important clinical diagnosis indexes of stroke,cerebral embolism or other typical cerebrovascular disease caused by the ischemia and hypoxia.The detections to them are used to locate the brain injury and assess the severity of the disease,etc.At present,the clinical routine examination techniques of cerebral hemodynamics parameters include digital subtraction angiography(DSA),positron emission tomography(PET),magnetic resonance to mography angiography(MRTA)and so on.Although they all have the high spatial resolution,there are the characteristics of radioactive radiation,complicated operation and high cost cause reproducible bedside detection of the cerebral hemodynamic parameters for a long time could not be implemented.Near Infrared Spectroscopy(NIRS),as a non-contact measurement technique based on the principle of light diffusion,has a working wavelength range of 780-1100 nm,being in line with the ‘biological window’ of the absorbance measurement to shallow tissue.That will avoid the influence of absorbance caused by water,fat and other material with a strong absorption of light and significantly improve the spectral data of the signal-to-noise ratio.Under the irradiatio n of the near infrared light source,the internal chromophore Hemoglobin(Hb)and other components of the body will lead to absorption and scattering and other physical reactions.By establishing a mathematical model of the spectral response of biological tissue,hemodynamic parameters such as blood flow and blood volume can be qualitatively and quantitatively analyzed.The near infrared spectroscopy has a high temporal resolution.In recent years,it has been paid more and more attention in the field of brain science.And at present,NIRS has been applied in the field of cerebral blood flow monitoring and neuroimaging.The continuous wave near-infrared spectroscopy is a kind of NIRS that take advantage of the constant intensity modulated light sourse.The CWNIRS,with a wide developing prospect for clinical monitoring and wearable medical,has many advantages like simple structured,convenient used and low cost.Indocyanine Green(IC G),as a no n-toxic or side effect dye,has ideal absorption properties in near-infrared wave band.According to its pharmacokinetic characteristics,ICG is regarded as an indicator in medical diagnosis.At the same time optical methods are used to measure its concentration changes to reflect the cardiovascular blood supply,liver reserve function and other physiological functions.A non-invasive detection method of cerebral hemodynamics parameters based on CWNIRS and IC G densitometry,CWNIRS-ICG,is put forward from the clinical demand of non-invasive and real-time detection of cerebral hemodynamic,which is built on CWNIRS absorption theory in tissue and dye dilution theory for ICG.O n the basis of the theoretical foundations,the establishment of the model,the optimization of the method,the system realization and the experimenta l verification,the paper studies the accurate construction of the chromatin concentration spectrum of the ICG in the brain tissue and the cerebral artery.And based on this,completes the detection system design of cerebral hemodynamics and experimental test analysis.The concrete research includes following contents:1、Study on the anti-fluctuate of subcutaneous blood flow measure ment method ofICG densitogram in cerebral tissue: On the basis of adsorption and scattering characteristics of CWNIRS,light transportation model in cerebral tissue is established.With modified Lambert-Beer law,a tri-wavelength photodetection method based on the detection depth difference principle was studied.To investigate the influence of the skin blood flow and tissue background light on the concentration spectrum of the brain tissue,a three-wavelength photoelectric detection method for detecting difference deep was studied.The regression and difference analysis is built to process the light absorption signal carrying the subcutaneous blood flow information and the complex light absorption signals containing superficial cerebral tissue information and subcutaneous capillaries information.And then,based on the MLBL,the modified model of the concentration spectrum to obtain anti-disturbance of subcutaneous blood flow ICG densitogram da ta in brain tissue is established.2 、 Study on the anti-fluctuate of blood oxygen measurement method of ICG densitogram in cerebral artery: According to pharmacokinetics characteristic of ICG in arterial flow,pulse spectrophotometric of subcutaneous cerebral arterial branch end is modeled based on Lambert-Beer law(LBL).Indicator densitometry signal,which is carring circulation and compensation information of cerebral artery,is detected noninvasively by pulse indicator densitometry.The anti-fluctuate of blood oxygen modified ICG densitogram in cerebral artery is calculated aiming at the fluctuation of local blood oxygen and hemoglobin concentration.3、Study on the processing and feature component extraction of pulse indicator density signals: According to the frequency features of pulse indicator density signals in cerebral artery,an adoptive feature component extraction algorithm SSE-EEMD is utilized.SSE-EEMD is a optimization method of ensemble empirical mode decomposition(EEMD)on the basis of singular spectrum entropy(SSE)analysis.Pulse indicator density signals are processed in EEMD under automatically identifying the best noise intensity added into original signal with the principle of the lowest SSE of reconstructed signals.The pulse feature is contained in the corresponding reconstructed signal of the lowest SSE,the reconstruction signal is used to improve the measurement accuracy of blood oxygen and ICG densitogram in cerebral artery.4、Study on the Calculation of Cerebral He modynamic Parameters Combined withNIRS and ICG densitometry(NIRS-ICG): O n the premise that ICG densitogram in both cerebral tissue and artery are accurately calculated,the rate of accumulation of the tracer substance in organ and the the quantity of the tracer introduced in time are obtained.The model of cerebral hemodynamic parameters was constructed with the Fick’s principle to calculate the cerebral blood flow(CBF),cerebral blood volume(C BV),mean transit time(MTT),blood flow index(BFI)and other parameters reflecting local cerebral blood supply and cerebral tissue oxygen saturation(c St O2)and cerebral arterial oxygen saturation(c Sa O2)and other parameters reflecting local cerebral oxygen supply.5、The design and imple mentation on cerebral hemodynamics parameters detection system based on CWNIRS-ICG: he detection system consists of two parts: one of that is the optolectric measurement platform for synchronous measurement of cerebral hemodynamics parameters characteristics of cerebral tissue and artery,the other one is dynamic analysis system of cerebral hemodynamics parameters.The tri-wavelength optolectric measuring equipment is covered on the forehead to detect the reflected signal,and the indicator density signals for cerebral tissue and artery carrying with cerebral hemodynamics status information are conditioned and transmited to principal computer.The software analysis system of the host computer is based on the common design and implementation of C# and MATLAB,which realizes the man-made control and detection process,efficiently processes the data and calculates the parameters,automatically stores the data and analyzes the results and implements the function of displaying cerebral hemodynamics parameters,etc.6 、 Evaluation of the research result by animal substitutive experiment for hypercapnia pathological model: Different concentration ratios of CO2 mixture air are mechanical ventilated into rabbit to establishment hypercapnia pathological model which cerebral blood and oxygen supply is in abnormal condition.CWNIRS-ICG method and its detection system is used to the upper pathological model to calculate the cerebral hemodynamic parameters of experimental animals.The consistency of parameters between CWNIRS-ICG and arterial blood gas(ABG)analysis is assessed.Comparing with the partial pressure of carbon dioxide(Pa CO2),the CBF,CBV and BFI results show strongly related even same trend to the change,but MTT have no coherence of the change.In addition,with the increase of CO2 concentration,the variation of the measured value of cerebral oxygen saturation is consistent with the change of the reference value analyzed with ABG.In summary,it is proved that CWNIRS-ICG is a feasible method for not only quantitatively analyzing at abnormal condition of cerebral blood flow and oxygen supply,but also providing evidence for localizing the cerebrovascular disease lesions or evaluating the disease severity.