Near-infrared Diffusion Spectroscopy And Its Application In Medicine

Diffuse optical techniques include diffuse optical spectroscopy(DOS)and diffuse correlation spectroscopy(DCS),which use near-infrared light(650nm-950nm)to investigate tissue physiology millimeters to centimeters below tissue surface non-invasively.DOS is a static technique that analyzes multispectral tissue-scattered light intensity signals with a photon diffusion approach or a Modified Beer-Lambert law approach to derive tissue oxy-hemoglobin,deoxy-hemoglobin,water,lipid,concentrations,etc,which are in turn used to compute tissue oxygen saturation and blood volume.DCS is a dynamic technique that analyzes rapid temporal fluctuations in tissue-scattered light with a correlation diffusion approach to derive tissue blood flow.Diffuse optical tomography(DOT)and diffuse correlation tomography(DCT)use high spatial density of source-detector pairs measure the distribution of tissue physiology.Since diffuse optical techniques have many advantages over tradition medical diagnose,such as noninvasive,safe,cheap,portable and continuous monitoring,they have been used to study brain diseases,brain imaging,cancers and muscle diseases.These works may improve modern medical diagnose greatly.This thesis concentrated on the studies of diffuse optical techniques and their novel medical applications.The main works include:1.The theory,instrument development,and clinic applications of diffuse optical techniques are reviewed.The popular clinic applications are breast cancer,brain diseases,and brain imaging,etc.2.The principle of DCS and DOS are fully demonstrated,including Monte Carlo method,diffuse light equation,and Modified Beer-Lambert law approach,which will help new researchers to conduct similar study.3.The calibration method of frequency-domain DOS is investigated.The results show the different control voltage of PMT and different PMT itself will influence the detection signal.The first step of calibration is getting the linear range of detection channel.The second step is using the diffuse theory and standard diffuse phantom to calibrate every detection channel.4.A novel DCS system based on software correlator is developed,which is validated by comparing with traditional DCS system using forearm cuff experiment.The blood flow index of normal forearm flexor tissue and artery occlusion forearm flexor tissue are measured which are 6.6x 10-9 cm2/s and 5.3x10-10 cm2/s respectively.These great difference of blood flow index may provide a way to differential the status of tissue ischemia.5.The cardiac pulse are clearly resolved by novel DCS system.Tissue blood flow from tissue absorption/scattering dynamics are separated by Modified Beer-Lambert law and thereby show that the origin of the pulsatile DCS signal is primarily blood flow(>90%).Through the SNR analysis,the time resolution of the novel DCS system is as quick as 200 Hz,which show the potential of novel DCS to study quick hemodynamic phenomenon.6.The cerebral autoregulation dynamics in one healthy volunteer is investigated by novel DCS system and noninvasive artery pressure monitor simultaneously.The rate of regulation is 0.66 sec;i.e.,a 66%change in resistance is required per second in order to autoregulate a 1%change in blood pressure.This may provide new way to monitor cerebral autoregulation dynamics and thereby diagnose brain diseases.7.The blood flow of exercising muscle is investigated by novel DCS system.The results show the moving muscle fiber will overestimate the blood flow index greatly.Novel DCS system can resolve the blood flow of static muscle in the exercise with high time resolution.The blood flow of dynamometer holding and dynamometer griping increase up to-2-3 times during exercise.This may be helpful to study muscle hemodynamics and sports medicine.