Wide-field modulated imaging for non-invasive quantification of tissue properties: A method development study.

摘要

Modulated Imaging (MI) is a recently reported method for rapid, non-invasive quantification of tissue optical properties (reduced scattering, micro?s and absorption, microa), which can be performed across a range of optical wavelengths to determine chromophore concentrations. In this thesis, development and characterization of a compact, low cost MI system is reported, using off-the-shelf hardware components with a custom software interface capable of easy modification for specific applications. This prototype setup consists of a color CCD camera which captures the diffusely reflected light from an object illuminated with patterns generated by a miniature projector. Broadband white light from the projector is delivered through a filter wheel containing narrowband filters for measurement at 420nm, 570nm, and 620nm wavelengths. A software application in MATLAB was written to control and synchronize the phase-shifted illumination patterns with image acquisition, and perform processing of image data into optical property maps. System accuracy was characterized by measuring a series of tissue simulating phantoms fabricated with varying micro's and microa, with both the prototype platform and a commercially available MI system as a reference. The overall error of the prototype system, for micro's ranging from 0.93-2.23mm-1 and microa ranging from 0.009-0.049mm -1, was approximately 10% and 16%, respectively. Utilizing a lookup table that requires measurements at two illumination spatial frequencies instead of performing a least-squares fit to diffuse reflectance measurements at ten frequencies reduced the acquisition and processing time by 80%, while reducing the accuracy of optical property determination by approximately 3%.;In summary, a prototype MI platform was developed and shown to be capable of quantifying the optical properties within biologically relevant micro's and microa ranges. The system was assembled for less than 10% of the cost of commercially available systems while enabling individual components to be upgraded for a wider range of accurate optical property determination. Scattering and absorption maps obtained at multiple wavelengths can subsequently be used to quantify the concentrations of various tissue chromophores including hemoglobin, water, and lipids. Non-invasive, image based acquisition of such information may have impact in medical applications, ultimately improving patient health through disease characterization and monitoring progress of treatment.