Spectrum Estimation Methods for Optical Doppler TomographyMultidimensional Digital Signal Processing ProblemWade SchwartzkopfOptical Doppler Tomography (ODT) is a method to obtain high resolution, three-dimensionaltomographic images of biological tissues. This method (Fig. 1) uses a modulated light source toraster scan a target tissue. Using a method such as the Short-Time Fourier Transform to obtainfrequency information in the reflected light (ΓODT(τ)), one can obtain images of the structure ofthe target tissue and of the velocity of fluids in the image.Photoreceiver (ΓODT(τ))2 x 2 SplitterFlow SampleMirror(dτ/dt=fo)ScanSLD (λο=850 nm, ∆λ=25 nm)He-Ne 2 x 1 SplitterA/D Converterδ2δ1Phase ModulatorComputer(Spectrogram)Figure 1: Prototype instrument to measure ODT interference fringe intensity (ΓODT(τ)).Further development of ODT will require substantially higher frame rates so that the methodcan be used in real-time clinical applications. One may be able to speed up the calculations forthe velocity image by only calculating whether or not there is flow and the direction of the flowrather than calculating the magnitude of the flow. However, there is a theoretical maximum limitof the frame rate dictated by physiological constraints from the blood flow velocity in the tissue.Using the interference fringe intensity (ΓODT(τ)) as input data, I will identify and evaluateseveral spectrum estimation procedures in the context of the flow hypothesis testing problemdescribed above; that is, how well they detect flow and the direction of flow. To accommodatetesting of spectrogram estimation procedures, simulated data will be provided. Once aninstrument is constructed in Dr. Milner’s laboratory at the University of Texas at Austin, thespectrogram estimation procedure and hypothesis testing may be applied using real input datarecorded from in vivo tissue samples.References Cited1. X. J. Wang, T.E. Milner, and J.S. Nelson. “Characterization of fluid flow velocity byoptical Doppler tomography,” Optics Letters, vol. 20, pp. 1337-1339, 1995.2. Z. Chen, T.E. Milner, D. Dave, and J.S. Nelson, “Optical Doppler tomographic imaging offluid flow velocity in highly scattering media,” Optics Letters, vol. 22, pp. 64-66, 1997.3. W.V. Sorin and D.M. Baney. “A simple noise reduction technique for optical low-coherence reflectometry,” IEEE Photonics Technology Letters, vol. 4, pp. 1404-1406,1992.4. J. Ramanathan and P. Topiwala. “Time-frequency localization and the spectrogram,”Applied and Computational Harmonic Analysis, vol. 1, pp. 209-215, 1994.5. F. Hlawatsch and G. F. Boudreaux-Bartels. “Linear and quadratic time-frequencyrepresentations,” IEEE Signal Processing Magazine, vol. 9, pp. 21-67,
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