Experimental Investigations On Determination Of Optical Properties In Tissues And Diffuse Light Imaging Based On Time-resolved Detection

The determination of tissue optical properties, such as absorption and reduced scattering coefficientsμa andμs'has drawn much attention in the biomedical optical field, for it will offer an important guidance of optical applications into clinic. The methodology that applies to determination of tissue optical properties and imaging with diffuse light currently includes three main measuring modes: continuous-wave, frequency-domain and time-resolved, of which, time-correlated single photon counting (TCSPC) has a lot of advantages that can provide more information than frequency-domain, such as it can separate contributions from the absorption coefficient and the sacttering one. In addition, compared with other imaging technique (such as MRI, X-CT), the Near-infrared (NIR) optical imaging is a no-invasive and on-line method. Moreover, the time-resolved measurements present an efficiency and high sensitivity in deriving more function information. TCSPC has been demonstrated a powerful technology for extracting the optical properties in tissues and for NIR optical imaging diagnosis.We briefly described a TCSPC system specifically designed for extracting the optical properties in tissues. Firstly, calibration of the time scale. Secondly, based on the mean time of flight and the variance of temporal profile measured by the TCSPC system, we used a simple and fast method to obtain the absorption coefficientμa and reduced scattering coefficientμs'of the turbid medium. The method could be applied for on-line monitoring of optical properties in tissues.Thirdly, this system and method were evaluated liquid tissue-simulating phantoms and solid phantoms. Furthermore, in vivo measurements were performed on several healthy volunteers to extract the optical properties and the oxygen saturation (SaO2) in forearm muscle. From our phantoms and in-vivo experiments, we concluded that the optical properties of tissue can be derived reasonably by the TCSPC system and the relevant inversion method.Finally, the featured parameters (such as the peak value, the intensity, the mean time of flight, the variance) of the temporal profile measured by the TCSPC system were very sensitive featured-data to monitor changes of the absorption and scattering occurring in the turbid medium. Chapter 5 of the thesis introduces these parameters in detail and study experimentally the imaging effect through phantoms. It is shown that the application of TCSPC to 2D imaging seems to be viable. It was also a fundamental of diffuse optical tomography and fluorescence molecular imaging.