Abstract
We describe the development of a rapid, noncontact imaging method, modulated imaging (MI), for quantitative, wide-field characterization of optical absorption and scattering properties of turbid media. MI utilizes principles of frequency-domain sampling and model-based analysis of the spatial modulation transfer function (s-MTF). We present and compare analytic diffusion and probabilistic Monte Carlo models of diffuse reflectance in the spatial frequency domain. Next, we perform MI measurements on tissue-simulating phantoms exhibiting a wide range of l values (0.5 mm to 3 mm) and (micro(s) (')micro(a)) ratios (8 to 500), reporting an overall accuracy of approximately 6% and 3% in absorption and reduced scattering parameters, respectively. Sampling of only two spatial frequencies, achieved with only three camera images, is found to be sufficient for accurate determination of the optical properties. We then perform MI measurements in an in vivo tissue system, demonstrating spatial mapping of the absorption and scattering optical contrast in a human forearm and dynamic measurements of a forearm during venous occlusion. Last, metrics of spatial resolution are assessed through both simulations and measurements of spatially heterogeneous phantoms.
Highlights
Light transport in tissues is a complex process due to multiple scattering and absorption
We describe a new imaging method, modulated imaging (MI), for quantitation and wide-field mapping of turbid media in the spatial frequency domain (SFD)
We present two homogeneous forward models of diffuse reflectance in the spatial frequency domain—the first, an analytic diffusion-based approach, and the second, a transport-based approach using Monte Carlo simulations
Summary
Light transport in tissues is a complex process due to multiple scattering and absorption. At the core of every optical technique for quantitative tissue characterization is the ability to separate optical absorption from optical scattering effects by the detection of a remitted or transmitted light field. This remission (or transmission) is a function of time and space, yielding two general classes of quantitative techniques: time-resolved and spatially resolved measurements, respectively (see Fig. 1). Spatially resolved measurements have been generally limited to the real spatial domain. The spatial point-spread function (s-PSF) is typically characterized by “multidistance” measurements,[6,7] tracking the spatial dependence of a reflected or transmitted light field generated from a point-like illumination. While recent work has shown the use of spatially structured illumination techniques for manipulating diffractive optical systems, 8 little has been reported for its use in characterization of diffusive systems. 9–11
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
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.
