Font Size: a A A

Research On The Improvement Of Sensitivity Of Continuous-wave Functional Near-infrared Spectroscopy

Posted on:2016-09-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:L ZhangFull Text:PDF
GTID:1108330467998545Subject:Biomedical engineering
Abstract/Summary:PDF Full Text Request
Noninvasive functional neuroimaging methods provide important tools for brain research. Compared with other functional neuroimaging methods, functional near-infrared spectroscopy (fNIRS) can provide high temporal resolution and reasonable spatial resolution. Besides, fNIRS places fewer limitations on the subjects and environment. So fNIRS is very suitable for brain-healthy studies. However, the current application of fNIRS is just the tip of the iceberg; the potential of fNIRS is far from fully exploited. The improvement of detection sensitivity will be the critical factor for promoting the application of fNIRS. This thesis focused on the improvement of sensitivity of continuous-wave functional near-infrared spectroscopy, and the main contents are as follows:(1) Studying these key issues affecting the quality of in vivo signal acquisition. This study analyzed the signal feature of the small regular fluctuation during measurement and deduced the production mechanism through mathematical methods, finding out the small regular fluctuation was resulted from frequency deviation of modulation frequency or sampling frequency. And the small regular fluctuation was eliminated by means of electric methods. This study analyzed the relationship between the numerical aperture of source/detector optical fiber and the quality of in vivo signal acquisition, concluded that the bigger the numerical aperture of source fiber or the smaller the numerical aperture of detector fiber, the better the quality of in vivo signal acquisition. This result can be used to guide the instrument design. The probe cap is one of the most important considerations for in vivo fNIRS signal acquisition. This study analyzed the design requirement of fNIRS cap carefully, and proposed two types optical fiber fastening methods for situations involving head movement or not and a practical fNIRS cap base material solution. Besides, this study proposed cap designs for multi-modality functional brain research combining fNIRS and other technology. (2) Developing a continuous wave fNIRS instrument with0.1pW noise equivalent power and more than100Hz temporal resolution, and verifying the brain activity measurement capability and the in vivo detection sensitivity. The instrument’s designing scheme involved simplifying instrument integration, digital lock-in detection with big sampling number, high-speed simultaneous sampling, improving control software (producer-consumer pattern, trading-space-for-time strategy, LABVIEW and MATLAB mixed programming), proposing design rules for modulation frequency and sampling frequency, design of ground and power supply, and so on. The vascular occlusion experiment validated the ability of the instrument to measure hemoglobin signal in vivo. The hemoglobin signal response for the reversing checkerboard visual task validated the ability to monitors brain activity noninvasively, and the detection result of optical neuronal signals in the visual cortex indicated that the instrument has excellent in vivo detection sensitivity.(3) Studying the brain’s functional architecture during an executive control task through fNIRS-based connectivity. A variety of data analysis methods were employed to establish the data analysis scheme to extract the information of the activity of the brain more comprehensively and effectively. The bilateral prefrontal cortex functional connectivity result during the color-word matching Stroop task validated the feasibility of fNIRS-based connectivity in high-level and complex cognitive tasks. The hemispheric lateralization was analyzed from multiple perspectives, including functional connectivity, activation, behavioral performance, as well as effective connectivity, which can describe the dynamic interaction of information of different brain regions. The results demonstrated that, with development of data analysis methods, fNIRS can detect brain functional information more sensitively.This study can help to exploit the capabilities of fNIRS effectively, promoting the application of fNIRS in neuroscience study, especially in clinical research.
Keywords/Search Tags:Functional near-infrared spectroscopy, Small regular fluctuation, Probe cap, Optical fiber, Functional connectivity, Effective connectivity
PDF Full Text Request
Related items