Joon S. You

Perturbation Monte Carlo methods to solve inverse photon migration problems in heterogeneous tissues

We introduce a novel and efficient method to provide solutions to inverse photon migration problems in heterogeneous turbid media. The method extracts derivative information from a single Monte Carlo simulation to permit the rapid determination of rates of change in the detected photon signal with respect to perturbations in background tissue optical properties. We then feed this derivative information to a nonlinear optimization algorithm to determine the optical properties of the tissue heterogeneity under examination. We demonstrate the use of this approach to solve rapidly a two-region inverse problem of photon migration in the transport regime, for which diffusion-approximation-based approaches are not applicable.

Perturbation and differential Monte Carlo methods for measurement of optical properties in a layered epithelial tissue model.

The use of perturbation and differential Monte Carlo (pMC/dMC) methods in conjunction with nonlinear optimization algorithms were proposed recently as a means to solve inverse photon migration problems in regionwise heterogeneous turbid media. We demonstrate the application of pMC/dMC methods for the recovery of optical properties in a two-layer extended epithelial tissue model from experimental measurements of spatially resolved diffuse reflectance. The results demonstrate that pMC/dMC methods provide a rapid and accurate approach to solve two-region inverse photon migration problems in the transport regime, that is, on spatial scales smaller than a transport mean free path and in media where optical scattering need not dominate absorption. The pMC/dMC approach is found to be effective over a broad range of absorption (50 to 400%) and scattering (70 to 130%) perturbations. The recovery of optical properties from spatially resolved diffuse reflectance measurements is examined for different sets of source-detector separation. These results provide some guidance for the design of compact fiber-based probes to determine and isolate optical properties from both epithelial and stromal layers of superficial tissues.

Use of the δ-P 1 approximation for recovery of optical absorption, scattering, and asymmetry coefficients in turbid media

We introduce a robust method to recover optical absorption, reduced scattering, and single-scattering asymmetry coefficients (microa, micros, g1) of infinite turbid media over a range of (micros/microa) spanning 3 orders of magnitude. This is accomplished through the spatially resolved measurement of irradiance at source-detector separations spanning 0.25-8 transport mean free paths (l*). These measurements are rapidly processed by a multistaged nonlinear optimization algorithm in which the measured irradiances are compared with predictions given by the delta-P1 variant of the diffusion approximation to the Boltzmann transport equation. The ability of the delta-P1 model to accurately describe radiative transport within media of arbitrary albedo and on spatial scales comparable to l* is the key element enabling the separation of g1 from micros.

Spatial-Frequency-Domain Imaging for quality assessment of apples

Spatial-Frequency-Domain Imaging (SFDI) is applied for the first time to the quality assessment of apples. The optical properties obtained are correlated to the physical and chemical properties.

Towards Functional Optical Imaging in Layered Tissues Using Modulated Imaging

We present forward modeling and measurement of spatially modulated illumination in layered turbid tissue systems to provide quantitative, depth-resolved functional information in tissues including cortex, retina and skin.

Quantitative determination of blood volume, oxygenation, and edema in port wine stain lesions

Clinical results suggest that quantiative mapping of vascular physiology and structures determined with Modulated imaging technique may be useful guide for effective treatments of Port-wine stains.

Towards 3D Mapping and Correction of Optical Properties in Turbid Media Based on Spatially Modulated Illumination

A simple technique for 3D mapping and correction of the absorption and reduced scattering coefficients in turbid media is suggested based on spatial patterns. Experimental results demonstrate the suggested technique.

Use of Perturbation Monte Carlo for Measurement of Optical Properties in an Extended Epithelial Tissue Model

A pMC based inverse solution for the determination of optical properties in an extended epithelial tissue model is experimentally validated.

Noninvasive imaging of oral premalignancy and malignancy

Objectives: Early detection of cancer and its curable precursors remains the best way to ensure patient survival and quality of life. Despite significant advances in treatment, oral cancer still results in 10,000 U.S. deaths annually, mainly due to the late detection of most oral lesions. Specific aim was to use a combination of non-invasive optical in vivo technologies to test a multi-modality approach to non-invasive diagnostics of oral premalignancy and malignancy. Methods: In the hamster cheek pouch model (120 hamsters), in vivo optical coherence tomography (OCT) and optical Doppler tomography (ODT) mapped epithelial, subepithelial and vascular change throughout carcinogenesis in specific, marked sites. In vivo multi-wavelength multi-photon (MPM) and second harmonic generated (SHG) fluorescence techniques provided parallel data on surface and subsurface tissue structure, specifically collagen presence and structure, cellular presence, and vasculature. Images were diagnosed by 2 blinded, pre-standardized investigators using a standardized scale from 0-6 for all modalities. After sacrifice, histopathological sections were prepared and pathology evaluated on a scale of 0-6. ANOVA techniques compared imaging diagnostics with histopathology. 95% confidence limits of the sensitivity and specificity were established for the diagnostic capability of OCT/ODT+ MPM/SHG using ROC curves and kappa statistics. Results: Imaging data were reproducibly obtained with good accuracy. Carcinogenesis-related structural and vascular changes were clearly visible to tissue depths of 2mm. Sensitivity (OCT/ODT alone: 71-88%; OCT+MPM/SHG: 79-91%) and specificity (OCT alone: 62-83%;OCT+MPM/SHG: 67-90%) compared well with conventional techniques. Conclusions: OCT/ODT and MPM/SHG are promising non-invasive in vivo diagnostic modalities for oral dysplasia and malignancy. Supported by CRFA 30003, CCRP 00-01391V-20235, NIH (LAMMP) RR01192, DOE DE903-91ER 61227, NIH EB-00293 CA91717, NSF BES-86924, AFOSR FA 9550-04-1-0101.