Linda T. Nieman

Fiber optic probe for polarized reflectance spectroscopy in vivo: Design and performance

We present the design and construction of a fiber optic probe for elastic light scattering spectroscopy in vivo with polarized excitation and polarization sensitive detection. The performance of the fiber probe is evaluated using a suspension of polystyrene spheres placed atop a diffusely scattering substrate, and it demonstrates that the size-dependent characteristics of the scatterers can be extracted in the presence of a highly diffusely scattering background using a linear combination of forward and backward Mie scattering components of the scatterers. Subsequently, Mie theory calculations are performed over a broad range of diagnostically relevant parameters of nuclei-mean diameter, size distribution, and relative refractive index-to understand how the polarized reflectance measurements with the fiber probe can be used to extract morphological information about epithelial tissue. Finally, the feasibility of in vivo measurements with the fiber optic based polarization sensitive light scattering spectroscopy is demonstrated.

Optical sectioning using a fiber probe with an angled illumination-collection geometry: evaluation in engineered tissue phantoms

We present a fiber optic probe that combines polarized illumination and detection with an angled distal probe geometry to detect the size-dependent scattering at a specific depth within epithelium. Analysis of the scattering signal by use of Mie theory allows the extraction of scatterer size and size distribution-key parameters for precancer detection. The probe was evaluated in two tissue phantoms: polystyrene beads atop collagen gel and multiple layers of cancer cells atop collagen. We also present in vivo measurements in the oral cavity of normal volunteers. The sizes of scatterers extracted from the scattering spectra corresponded to independently measured values.

An apertureless near-field scanning optical microscope and its application to surface-enhanced Raman spectroscopy and multiphoton fluorescence imaging

We describe a home-built apertureless near-field scanning optical microscope and present preliminary results of its operation. Raman scattering from samples of polydiacetylene para-toluene sulphonate, and two-photon-induced fluorescence from crystallites of coumarin I dye are strongly enhanced in the presence of a sharp gold-coated atomic force microscope tip. We verify the dependence of the scattered intensity on the polarization of the incident beam relative to the tip axis. Finally, we show near-field fluorescence images taken in the presence of a strong far-field background whose spatial resolution is limited by the size of the tip.

Polarized Reflectance Spectroscopy for Pre-Cancer Detection

Early detection of cancer and its curable precursors remains the best way to ensure patient survival and quality of life. Thus, highly selective, sensitive and cost-effective screening and diagnostic techniques to identify curable pre-cancerous lesions are desperately needed. Precancers are characterized by increased nuclear size, increased nuclear/cytoplasmic ratio, hyperchromasia and pleomorphism, which currently can only be assessed through an invasive, painful biopsy. Here, we describe the development of a non-invasive optical technique based on polarized reflectance spectroscopy that has the potential to provide in real time diagnostically useful information for pre-cancer detection. Our results demonstrate that polarized reflectance spectroscopy can be used to selectively detect the size-dependent scattering characteristics of nuclei in vivo. We gradually progress from cell suspensions to realistic three-dimensional tissue models of epithelium, then to cervical biopsies and, finally to in vivo studies on normal volunteers and clinical patients.

Compact beveled fiber optic probe design for enhanced depth discrimination in epithelial tissues

We report the development and evaluation of a simple compact probe that incorporates multiple beveled fibers for depth sensitive detection of spectroscopic signals in vivo. We evaluated three probes with bevel angles 35, 40, and 45 degrees for their collection efficiency and depth resolution using a thin highly scattering white substrate and found that a 40 degree bevel provides the best characteristics for depth-resolved spectroscopy. The depth sensitivity of the probe with 40 degree beveled fibers was then evaluated using multilayer phantoms with scattering properties mimicking precancerous tissue and in vivo on normal human oral mucosa. The results demonstrate that the use of multiple beveled fibers has the capability to simultaneously collect scattering spectra from a range of depths within epithelial tissue that has the potential to provide further significant improvement of detection and monitorin of epithelial precancers.

AI in Clinical Decision Support: Applications in Optical Spectroscopy for Cancer Detection and Diagnosis

Optical approaches have been studied for the detection and diagnosis of epithelial cancer. Due to the biochemical and structural changes that occur in cancerous cells, malignant, benign, and normal tissues have different spectral properties. Artificial intelligence (AI) methods are being explored to detect and diagnose cancer based on optical imaging and spectra. AI is also used to optimize the design of optical spectroscopy and imaging instrumentation. In this chapter, we review the literature on AI applied to optical spectroscopy for cancer detection and diagnosis and present a detailed case study of research on oral cancer diagnosis using polarized light spectra.

Oblique polarized reflectance spectroscopy for depth sensitive measurements in the epithelial tissue

Optical spectroscopy has shown potential as a tool for precancer detection by discriminating alterations in the optical properties within epithelial tissues. Identifying depth-dependent alterations associated with the progression of epithelial cancerous lesions can be especially challenging in the oral cavity due to the variable thickness of the epithelium and the presence of keratinization. Optical spectroscopy of epithelial tissue with improved depth resolution would greatly assist in the isolation of optical properties associated with cancer progression. Here, we report a fiber optic probe for oblique polarized reflectance spectroscopy (OPRS) that is capable of depth sensitive detection by combining the following three approaches: multiple beveled fibers, oblique collection geometry, and polarization gating. We analyze how probe design parameters are related to improvements in collection efficiency of scattered photons from superficial tissue layers and to increased depth discrimination within epithelium. We have demonstrated that obliquely-oriented collection fibers increase both depth selectivity and collection efficiency of scattering signal. Currently, we evaluate this technology in a clinical trial of patients presenting lesions suspicious for dysplasia or carcinoma in the oral cavity. We use depth sensitive spectroscopic data to develop automated algorithms for analysis of morphological and architectural changes in the context of the multilayer oral epithelial tissue. Our initial results show that OPRS has the potential to improve the detection and monitoring of epithelial precancers in the oral cavity.

Adaptive spectral window sizes for feature extraction from optical spectra

We propose an approach to adaptively adjust the spectral window size used to extract features from optical spectra. Previous studies have employed spectral features extracted by dividing the spectra into several spectral windows of a fixed width. However, the choice of spectral window size was arbitrary. We hypothesize that by adaptively adjusting the spectral window sizes, the trends in the data will be captured more accurately. Our method was tested on a diffuse reflectance spectroscopy dataset obtained in a study of oblique polarization reflectance spectroscopy of oral mucosa lesions. The diagnostic task is to classify lesions into one of four histopathology groups: normal, benign, mild dysplasia, or severe dysplasia (including carcinoma). Nine features were extracted from each of the spectral windows. We computed the area (AUC) under Receiver Operating Characteristic curve to select the most discriminatory wavelength intervals. We performed pairwise classifications using Linear Discriminant Analysis (LDA) with leave-one-out cross validation. The results showed that for discriminating benign lesions from mild or severe dysplasia, the adaptive spectral window size features achieved AUC of 0.84, while a fixed spectral window size of 20 nm had AUC of 0.71, and an AUC of 0.64 is achieved with a large window size containing all wavelengths. The AUCs of all feature combinations were also calculated. These results suggest that the new adaptive spectral window size method effectively extracts features that enable accurate classification of oral mucosa lesions.

Fiber optic probe for polarized reflectance spectroscopy: oral mucosa studies

We describe a new clinical instrument based on polarized reflectance spectroscopy for the early detection of cancerous and precancerous lesions of the oral mucosa.