Imaging of light scattering tissues with fluorescent contrast agents

Abstract

A system and method for non-invasive biomedical optical imaging and spectroscopy with low-level light is described. The technique includes a modulated light source coupled to tissue to introduce excitation light. Fluorescent light emitted in response to the excitation light is detected with a sensor. The AC intensity and phase of the excitation and detected fluorescent light is provided to a processor operatively coupled to the sensor. A processor employs the measured emission kinetics of excitation and fluorescent light to “map” the spatial variation of one or more fluorescence characteristics of the tissue and generate a corresponding image of the tissue via an output device. The fluorescence characteristic may be provided by exogenous contrast agents, endogenous fluorophores, or both. A technique to select or design an exogenous fluorescent contrast agent to improve image contrast is also disclosed.

1 .- 33 . (canceled) 
     
     
         34 . A method, comprising:
 evaluating ability of a number of fluorescent agents to provide image contrast between different tissue types, said evaluating including determining a relationship between degree of image contrast and at least one of fluorescence lifetime or fluorescence yield of the agent;   selecting one of the agents based on said evaluating; and   providing the selected one of the agents for introduction into a biologic tissue to enhance imaging performed in accordance with a mathematical expression modeling the behavior of multiply scattered light traveling through the tissue.   
     
     
         35 . The method of  claim 34 , wherein the at least one is fluorescence lifetime. 
     
     
         36 . The method of  claim 34 , wherein the mathematical expression corresponds to a diffusion equation approximation of multiply scattered light. 
     
     
         37 . The method of  claim 36 , further comprising applying the diffusion equation approximation in a frequency domain form. 
     
     
         38 . The method of  claim 34 , further comprising generating an image of the tissue by mapping spatial variation of a level of a fluorescence characteristic of the tissue. 
     
     
         39 . The method of  claim 34 , wherein the mathematical expression is in a frequency domain form and the image contrast is provided in terms of at least one of phase shift contrast or modulation contrast. 
     
     
         40 . A method, comprising:
 exposing a biologic tissue to a first excitation light;   detecting a first emission from the tissue in response to the first excitation light;   introducing a fluorescent contrast agent into the tissue after said detecting;   exposing the tissue after said introducing to a second excitation light;   sensing a second emission in response to the second excitation light;   comparing data corresponding to the first emission with data corresponding to the second emission to evaluate contrast provided by the agent as a function of at least one of fluorescence lifetime, fluorescence yield, or quantum efficiency.   
     
     
         41 . The method of  claim 40 , wherein the at least one is fluorescence lifetime. 
     
     
         42 . The method of  claim 41 , wherein the fluorescence lifetime is in a range of about 0.1 to 10 nanoseconds. 
     
     
         43 . The method of  claim 41 , wherein the fluorescence lifetime is in a range of about 0.5 to 5 nanoseconds. 
     
     
         44 . The method of  claim 41 , wherein the fluorescence lifetime is in a range of about 0.2 to 2 nanoseconds. 
     
     
         45 . The method of  claim 40 , further comprising evaluating the first and second emissions with a mathematical expression modeling the behavior of multiply scattered light traveling through the tissue. 
     
     
         46 . The method of  claim 45 , wherein the mathematical expression corresponds to a diffusion equation approximation of multiply scattered light. 
     
     
         47 . The method of  claim 40 , further comprising generating an image of the tissue by mapping spatial variation of a level of a fluorescence characteristic of the tissue. 
     
     
         48 . The method of  claim 47 , wherein the fluorescence characteristic is at least one of fluorescence lifetime, fluorescence yield, or fluorescence quantum efficiency. 
     
     
         49 . The method of  claim 47 , wherein said generating includes determining a modulation amplitude change and a phase change of the light emission relative to the excitation light. 
     
     
         50 . The method of  claim 49 , wherein the fluorescence characteristic corresponds to the fluorescence lifetime. 
     
     
         51 . The method of  claim 40 , wherein wavelength of the first excitation light is generally the same as wavelength of fluorescent light emitted by the agent in response to the second excitation light.