Tyler K. Drake

Evaluation of hybrid algorithm for analysis of scattered light using ex vivo nuclear morphology measurements of cervical epithelium.

We evaluate a new hybrid algorithm for determining nuclear morphology using angle-resolved low coherence interferometry (a/LCI) measurements in ex vivo cervical tissue. The algorithm combines Mie theory based and continuous wavelet transform inverse light scattering analysis. The hybrid algorithm was validated and compared to traditional Mie theory based analysis using an ex vivo tissue data set. The hybrid algorithm achieved 100% agreement with pathology in distinguishing dysplastic and non-dysplastic biopsy sites in the pilot study. Significantly, the new algorithm performed over four times faster than traditional Mie theory based analysis.

Multiplexed low coherence interferometry instrument for measuring microbicide gel thickness distribution

We present a Fourier-domain, multiplexed low coherence interferometry (LCI) instrument designed for application to intravaginal measurement of microbicidal gel distribution. Microbicide gels are topical products developed to combat sexually transmitted diseases, such as HIV/AIDS, by acting as delivery vehicles for active drugs and barrier layers to vaginal tissue. Measuring microbicide gel vaginal distribution is key to understanding the gels biological effectiveness. This study presents a new LCI system for measuring gel distribution that uses six multiplexed channels to achieve broad area scanning without the need for a mechanical scanner. The presented results characterize the performance of the Fourier-domain multiplexed LCI system in measuring gel thickness distribution. The system demonstrates good optical signal-to-noise ratio, steady performance across all channels, negligible cross talk, and accurate measurement with micrometer scale resolution. The potential impact of using a multiplexed LCI system for in vivo measurements is also discussed.

Wavelet transform fast inverse light scattering analysis for size determination of spherical scatterers

We present a fast approach for size determination of spherical scatterers using the continuous wavelet transform of the angular light scattering profile to address the computational limitations of previously developed sizing techniques. The potential accuracy, speed, and robustness of the algorithm were determined in simulated models of scattering by polystyrene beads and cells. The algorithm was tested experimentally on angular light scattering data from polystyrene bead phantoms and MCF-7 breast cancer cells using a 2D a/LCI system. Theoretical sizing of simulated profiles of beads and cells produced strong fits between calculated and actual size (r(2) = 0.9969 and r(2) = 0.9979 respectively), and experimental size determinations were accurate to within one micron.

Time-resolved imaging refractometry of microbicidal films using quantitative phase microscopy.

Quantitative phase microscopy is applied to image temporal changes in the refractive index (RI) distributions of solutions created by microbicidal films undergoing hydration. We present a novel method of using an engineered polydimethylsiloxane structure as a static phase reference to facilitate calibration of the absolute RI across the entire field. We present a study of dynamic structural changes in microbicidal films during hydration and subsequent dissolution. With assumptions about the smoothness of the phase changes induced by these films, we calculate absolute changes in the percentage of film in regions across the field of view.

Feasibility of clinical detection of cervical dysplasia using angle‐resolved low coherence interferometry measurements of depth‐resolved nuclear morphology

This study sought to establish the feasibility of using in situ depth‐resolved nuclear morphology measurements for detection of cervical dysplasia. Forty enrolled patients received routine cervical colposcopy with angle‐resolved low coherence interferometry (a/LCI) measurements of nuclear morphology. a/LCI scans from 63 tissue sites were compared to histopathological analysis of co‐registered biopsy specimens which were classified as benign, low‐grade squamous intraepithelial lesion (LSIL), or high‐grade squamous intraepithelial lesion (HSIL). Results were dichotomized as dysplastic (LSIL/HSIL) versus non‐dysplastic and HSIL versus LSIL/benign to determine both accuracy and potential clinical utility of a/LCI nuclear morphology measurements. Analysis of a/LCI data was conducted using both traditional Mie theory based processing and a new hybrid algorithm that provides improved processing speed to ascertain the feasibility of real‐time measurements. Analysis of depth‐resolved nuclear morphology data revealed a/LCI was able to detect a significant increase in the nuclear diameter at the depth bin containing the basal layer of the epithelium for dysplastic versus non‐dysplastic and HSIL versus LSIL/Benign biopsy sites (both p < 0.001). Both processing techniques resulted in high sensitivity and specificity (>0.80) in identifying dysplastic biopsies and HSIL. The hybrid algorithm demonstrated a threefold decrease in processing time at a slight cost in classification accuracy. The results demonstrate the feasibility of using a/LCI as an adjunctive clinical tool for detecting cervical dysplasia and guiding the identification of optimal biopsy sites. The faster speed from the hybrid algorithm offers a promising approach for real‐time clinical analysis.

Design and validation of a multiplexed low coherence interferometry instrument for in vivo clinical measurement of microbicide gel thickness distribution

We present a multiplexed, Fourier-domain low coherence interferometry (mLCI) instrument for in vivo measurement of intravaginal microbicide gel coating thickness distribution over the surface of the vaginal epithelium. The mLCI instrument uses multiple delivery fibers to acquire depth resolved reflection profiles across large scanned tissue areas. Here mLCI has been adapted into an endoscopic system with a custom imaging module for simultaneous, co-registered measurements with fluorimetric scans of the same surface. The resolution, optical signal-to-noise, and cross-talk of the mLCI instrument are characterized to evaluate performance. Validation measurements of gel thickness are made using a calibration socket. Initial results from a clinical study are presented to show the in vivo capability of the dual-modality system for assessing the distribution of microbicide gel vehicles in the lower human female reproductive tract.

Measuring Dilution of Microbicide Gels with Optical Imaging

We present a novel approach for measuring topical microbicide gel dilution using optical imaging. The approach compares gel thickness measurements from fluorimetry and multiplexed low coherence interferometry in order to calculate dilution of a gel. As a microbicide gel becomes diluted at fixed thickness, its mLCI thickness measurement remains constant, while the fluorimetry signal decreases in intensity. The difference between the two measurements is related to the extent of gel dilution. These two optical modalities are implemented in a single endoscopic instrument that enables simultaneous data collection. A preliminary validation study was performed with in vitro placebo gel measurements taken in a controlled test socket. It was found that change in slope of the regression line between fluorimetry and mLCI based measurements indicates dilution. A dilution calibration curve was then generated by repeating the test socket measurements with serial dilutions of placebo gel with vaginal fluid simulant. This methodology can provide valuable dilution information on candidate microbicide products, which could substantially enhance our understanding of their in vivo functioning.

In vivo optical imaging of human vaginal gel thickness distributions with a probe-based, dual-modality instrument.

Abstract. We used a probe-based dual-modality optical imaging instrument to measure in vivo coating thickness distributions of a gel distributed along the vaginal lumen, in a clinical study. The gel was a surrogate for one delivering an anti-HIV topical microbicide. Imaging data from Fourier-domain multiplexed low-coherence interferometry (mLCI) and fluorimetric measurements were compared to assess the feasibility and accuracy of mLCI in measuring in vivo gel coating thickness distributions. In each study session, 3.5 mL of Replens gel was inserted to the vaginal fornix while the participant was supine. The participant either: 1. remained supine (10 or 60 min); or 2. sat up (1 min), stood up (1 min), sat down (1 min) and returned to the supine position; net elapsed time was 10 or 60 min after which the gel distribution was imaged. Local coating thickness distributions were qualitatively and quantitatively similar. Here mLCI did not accurately measure thicker gel coatings (>0.8  mm), a limitation not seen with fluorimetry. However, mLCI is capable of measuring in vivo microbicide gel distributions with resolution on the order of 10 μm, without the need for exogenous contrast agents, and can accurately capture relevant summary coating measures in good agreement with fluorimetry.

Development of an integrated endoscopic device for multiplexed low coherence interferometry measurements of microbicide gel coating thickness

Microbicide gels are topical products that have recently been developed to combat sexually transmitted diseases including HIV/AIDS. The extent of gel coverage, thickness, and structure are crucial factors in gel effectiveness. It is necessary to be able to monitor gel distribution and behavior under various circumstances, such as coatis, and over an extended time scale in vivo. We have developed a multiplexed, Fourier-domain low coherence interferometry (LCI) system as a practical method of measuring microbicide gel distribution, with precision and accuracy comparable to currently used fluorometric techniques techniques. The multiplexed system achieved a broad scanning area without the need for a mechanical scanning device, typical of OCT systems, by utilizing six parallel channels with simultaneous data collection. We now propose an imaging module which will allow the integration of the multiplexed LCI system into the current fluorescence system in conjunction with an endoscope. The LCI imaging module will meet several key criteria in order to be compatible with the current system. The fluorescent system features a 4-mm diameter rigid endsoscope enclosed in a 27-mm diameter polycarbonate tube, with a water immersion tip. Therefore, the LCI module must be low-profile as well as water-resistant to fit inside the current design. It also must fulfill its primary function of delivering light from each of the six channels to the gel and collecting backscattered light. The performance of the imaging module will be characterized by scanning a calibration socket which contains grooves of known depths, and comparing these measurements to the fluorometric results.

Wavelet Transform Based Fast Inverse Light Scattering Analysis for Size Determination of Spherical Scatterers

We present a fast approach for size determination of spherical scatterers using the continuous wavelet transform of the angular scattering profile and compare its accuracy, speed, and robustness to Mie theory and T-matrix based analysis.