Abstract
The optical properties of brain tissues have been evaluated by measuring the phase velocity and attenuation of harmonically modulated light. The phase velocity for photon density waves at 650-nm wavelength has been found to be in the range of 5 to 12% of the corresponding velocity in a nonscattering medium, and the optical penetration depth was in the range 2.9 to 5.2 mm. These results are used to predictthe resolution of optical imaging of deep tissue structures by diffusely propagating incoherent photons. The results indicate that structures of a few millimeters in linear dimension can be identified at 10 mm depth provided that proper wavelength and time resolution are selected. This depth can possibly be enlarged to 30 mm in the case of tissues with very low scattering such as in the case of the neonatal human brain.
Highlights
Optical techniques represent a valuable tool for in vivo analysis of tissue properties and for imaging of tissue structures . ,2 Recent developments have emphasized dynamic measurements where either an ultrashort laser pulse or highfrequency amplitude-modulated laser light is launched into the tissue.[38]
The phase velocity for photon density waves at 650-nm wavelength has been found to be in the range of 5 to 12% of the corresponding velocity in a nonscattering medium, and the optical penetration depth was in the range 2.9 to 5.2 mm
The results indicate that structures of a few millimeters in linear dimension can be identified at 10 mm depth provided that proper wavelength and time resolution are selected
Summary
Optical techniques represent a valuable tool for in vivo analysis of tissue properties and for imaging of tissue structures . ,2 Recent developments have emphasized dynamic measurements where either an ultrashort laser pulse or highfrequency amplitude-modulated laser light is launched into the tissue.[38]. This paper considers the advantages as well as the limitations of using diffusely propagating incoherently scattered light for evaluation of tissue properties and for imaging.6'7'9. Irridiation with harmonically modulated optical beams will initiate density waves of diffusely propagating photons. The velocity of these waves, which is strongly dependent on the modulation frequency, can typically vary from the velocity of light as an upper limit, down to about 5% of. We will demonstrate that image resolution in the time domain can be significantly improved by receiving only the first part of the diffuse transmitted light and that the resolution can be further improved by using an optical wavelength that is optimally selected with respect to the scattering and absorption coefficient.3'1012 This paper, will be limited to the diffusion approximation. Diffusion theory only accounts for heavily scattered photons that propagate with a reduced effective velocity
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
