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List of Research Abstracts
Dhalla, Al-Hafeez - Novel calibration techniques for frequency-domain diffuse optical spectroscopy in a side-firing geometry
Title: Novel calibration techniques for frequency-domain diffuse optical spectroscopy in a side-firing geometry
Al-Hafeez Dhalla
BME 2007
Supervising Professor: Dr. Nimmi Ramanjum
Abstract:
Previous research in this laboratory has described a side-firing fiber optic sensor based
on near-infrared spectroscopy for guiding core needle breast biopsy procedures. A
frequency-domain photon migration infrared instrument is used to measure optical
properties of breast tissue through an aperture in the biopsy needle before the tissue is
removed for histology. Real-time algorithms provide quantitative tissue physiology
measurements (hemoglobin saturation, tissue scattering, etc.) to aid a radiologist in
needle positioning. Two new calibration methods have been developed to improve the
accuracy of these measurements. Both methods require the use of an array of large volume
tissue phantoms with well characterized absorption (ma) and reduced scattering (ms') In
this study, India ink and Intralipid were used to fabricate the phantoms after being
separately characterized by a spectrometer and custom designed diffuse reflectance
measurement apparatus, respectively. Both calibration methods apply corrections to the
measured data and can be used in tandem. The first calibration is performed by deriving
three correction factors that are applied to the separated frequency-dependant amplitude
attenuation and phase delay measurements. Specifically, these are additive and
multiplicative corrections to the amplitude attenuation measurement and an additive
frequency dependant ramp of variable slope to the phase delay measurement. The second
correction involves placing different relative weights on the amplitude and phase data in
the fitting and extraction algorithms. This weighting was applied both as a constant
across all modulation frequencies and as a frequency dependant linear function. Using
these calibration techniques, mean extraction accuracies of 5% for absorption and 2% for
reduced scattering were realized in tissue phantoms.
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