Molecular imaging using fluorescence spectroscopy-based techniques is
generally inefficient due to the low quantum yield of most naturally occurring
biomolecules. Current fluorescence imaging techniques tag these biomolecules
chemically or through genetic manipulation, increasing the complexity of the system. A
technique capable of imaging these biomolecules without modifying the chromophore
and/or its environment could provide vital biometric parameters and unique insights into
various biological processes at a molecular level.
Pump probe spectroscopy has been used extensively to study the molecular
properties of poorly fluorescing biomolecules, because it utilizes the known absorption
spectrum of these chromophores. Optical Coherence Tomography (OCT) is an optical
imaging modality that harnesses the power of low coherence interferometry to measure
the 3-D spatially resolved reflectivity of a tissue sample. We plan to develop a new
molecular imaging modality that combines these techniques to provide 3-D, highresolution
molecular images of various important biomolecules. The system uses a Fourier domain OCT setup with a modified sample arm that
combines the "pump" and "probe" beams. The pump beam drives the molecules from
the ground state to excited state and the probe interrogates the population change due to
the pump and is detected interferometrically. The pump and the probe beam
wavelengths are optimized to maximize absorption at the pump wavelength and
maximize the penetration depth at the probe wavelength. The pump-probe delay can be
varied to measure the rate at which the excited state repopulates the ground state, i.e., the
ground state recovery time. The ground state recovery time varies for different
chromophores and can potentially be used to identify different biomolecules.
The system was designed and optimized to increase the SNR of the PPOCT
signals. It was tested by imaging hemoglobin and melanin samples and yielded
encouraging results. Potential applications of imaging hemoglobin using this technique
include the mapping of tissue microvasculature and measuring blood-oxygen saturation
levels. These applications could be used to identify hypoxic areas in tissue. Melanin
imaging can provide means of demarcation of melanoma in various organs such as skin,
eye and intestines.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-05-796 |
| Date | 16 January 2010 |
| Creators | Jacob, Desmond |
| Contributors | Applegate, Brian E. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis |
| Format | application/pdf |
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