High-resolution optical molecular imaging has become a vital tool for understanding and measuring physiologically
important biometrics on the cellular and subcellular level. In spite of significant recent advances in microscopy,
molecular imaging of most endogenous biomolecular species remains elusive. Directly imaging endogenous
biomolecules without the aid of exogenous tags is highly desirable. We developed pump-probe optical coherence
microscopy (PPOCM) based on our previous success in integrating pump-probe absorption spectroscopy with
optical coherence tomography. A fixed human skin tissue with melanoma was imaged by the PPOCM system. The
preliminary results show that PPOCM can provide better can clear contrast between normal tissue and melanoma
than OCM. This system also can be used to image other chromophores.
The overall goal for this project is the development and study of a quantitative fluorescence sensor for in vivo detection
of β-amyloid (Aβ), the primary protein component of senile plaques in Alzheimer's disease (AD). Toward achieving
that goal a Monte Carlo simulation has been developed to model photon propagation through the human head and a
phantom model of the human head has been built and tested. In both cases a four layer model that included the skin,
skull, fluorescent biosensor, and gray matter was used. A sensitivity study was performed to investigate the influence on
the fluorescent output intensity of changes in concentration of the sensor. The results show that the fluorescent output
intensity is detectable with a reasonable fluorescent sensor concentration and increases nearly linearly with increases in
fluorescent concentration in the sensor. These results imply that the sensor would be detectable through the head using a
reasonable optical system. The overall results are being used to aid in the design of the fluorescent sensor and the
optical system for early detection of AD.
The increasing prevalence of diabetes in the United States has led many to pursue methods for non-invasive glucose detection using various optical approaches such as NIR absorption spectroscopy, Raman spectroscopy, fluorescence spectroscopy, and polarization. Polarization approaches using the aqueous humor as the sensing site have been previously shown to achieve 5 mg/dl accuracy in vitro, however accuracy in vivo has yet to be obtained due to motion induced birefringence changes in the cornea. A dual-wavelength close-looped system was developed to compensate for motion artifact. This method has shown 15 mg/dl accuracy in the presence of birefringence changes in the optical path in vitro similar to those that occur in the cornea -- something previous systems were not capable of doing.
In a continuing effort to develop a noninvasive means of monitoring glucose levels using the aqueous humor of the eye, a dual-wavelength system is developed to show that varying birefringence, similar to what is seen with a moving cornea, can be compensated. In this work, a dual-wavelength, closed-loop system is designed and a model is developed to extract the glucose concentration information. The system and model are tested using various concentrations of glucose in a birefringent test cell subject to motion artifact. The results show that for a static, nonmoving sample, glucose can be predicted to within 10 mg/dl for the entire physiologic range (0 to 600 mg/dl) for either laser wavelength (523 or 635 nm). In the presence of moving birefringence, each individual wavelength produces standard errors on the order of a few thousand mg/dL. However, when the two wavelengths are combined into the developed model, this error is less than 20 mg/dL. The approach shows that multiple wavelengths can be used to drastically reduce the error in the presence of a moving birefringent sample and thus may have the potential to be used to noninvasively monitor glucose levels in vivo in the presence of moving corneal birefringence.