Angle-resolved low-coherence interferometry: an optical biopsy technique for clinical detection of dysplasia in Barrett's esophagus

Next-generation endoscopic probe for detection of esophageal dysplasia using combined OCT and angle-resolved low-coherence interferometry

Angle-resolved low-coherence interferometry (a/LCI) is an optical technique that enables depth-specific measurements of nuclear morphology, with applications to detecting epithelial cancers in various organs. Previous a/LCI setups have been limited by costly fiber-optic components and large footprints. Here, we present a novel a/LCI instrument incorporating a channel for optical coherence tomography (OCT) to provide real-time image guidance. We showcase the system's capabilities by acquiring imaging data from in vivo Barrett's esophagus patients. The main innovation in this geometry lies in implementing a pathlength-matched single-mode fiber array, offering substantial cost savings while preserving signal fidelity. A further innovation is the introduction of a specialized side-viewing probe tailored for esophageal imaging, featuring miniature optics housed in a custom 3D-printed enclosure attached to the tip of the endoscope. The integration of OCT guidance enhances the precision of tissue targeting by providing real-time morphology imaging. This novel device represents a significant advancement in clinical translation of an enhanced screening approach for esophageal precancer, paving the way for more effective early-stage detection and intervention strategies.

Advanced endoscopic imaging for detecting and guiding therapy of early neoplasias of the esophagus

Esophageal cancers, largely adenocarcinoma in Western countries and squamous cell cancer in Asia, present a significant burden of disease and remain one of the most lethal of cancers. Key to improving survival is the development and adoption of new imaging modalities to identify early neoplastic lesions, which may be small, multifocal, subsurface, and difficult to detect by standard endoscopy. Such advanced imaging is particularly relevant with the emergence of ablative techniques that often require multiple endoscopic sessions and may be complicated by bleeding, pain, strictures, and recurrences. Assessing the specific location, depth of involvement, and features correlated with neoplastic progression or incomplete treatment may optimize treatments. While not comprehensive of all endoscopic imaging modalities, we review here some of the recent advances in endoscopic luminal imaging, particularly with surface contrast enhancement using virtual chromoendoscopy, highly magnified subsurface imaging with confocal endomicroscopy, optical coherence tomography, elastic scattering spectroscopy, angle-resolved low-coherence interferometry, and light scattering spectroscopy. While there is no single ideal imaging modality, various multimodal instruments are also being investigated. The future of combining computer-aided assessments, molecular markers, and improved imaging technologies to help localize and ablate early neoplastic lesions shed hope for improved disease outcome.

Spatial scanning of a sample with two-dimensional angle-resolved low-coherence interferometry for analysis of anisotropic scatterers

Angle-resolved low-coherence interferometry (a/LCI) measures depth-resolved angular scattering for cell nuclear morphology analysis. 2D a/LCI, developed to collect across two scattering planes, is currently limited by the lack of spatial scanning. Here we demonstrate 2D a/LCI scanning across a three-dimensional volume using an image rotation scheme and a scanning mirror. Validation using various optical phantoms demonstrated excellent scatterer size determination over a 7.5 mm linear range, for a total accessible area of ∼44 mm². Measurements from anisotropic scatterers allowed accurate determination of sizes and computation of aspect ratios. This scanning system will facilitate analysis of scatterer structure across wider tissue areas.

Reconstruction of angle-resolved backscattering through a multimode fiber for cell nuclei and particle size determination

We demonstrate reconstruction of angle-resolved optical backscattering after transmission through a multimode fiber. Angle-resolved backscattering is an important tool for particle sizing, and has been developed as a diagnostic modality for detecting epithelial precancer. In this work, we fully characterized the transfer function of a multimode fiber using a plane-wave illumination basis across two dimensions. Once characterized, angle-resolved scattering information which has been scrambled by multimodal propagation can be easily and accurately reconstructed. Our technique was validated using a Mie theory-based inverse light scattering analysis (ILSA) algorithm on polystyrene microsphere phantoms of known sizes. To demonstrate the clinical potential of this approach, nuclear morphology was determined from the reconstructed angular backscattering from MCF-10A human mammary epithelial cell samples and validated against quantitative image analysis (QIA) of fluorescence microscopy images.

Angular range, sampling and noise considerations for inverse light scattering analysis of nuclear morphology

In recent years, significant work has been devoted to the use of angle-resolved elastic scattering for the extraction of nuclear morphology in tissue. By treating the nucleus as a Mie scattering object, techniques such as angle-resolved low-coherence interferometry (a/LCI) have demonstrated substantial success in identifying nuclear alterations associated with dysplasia. Because optical biopsies are inherently noninvasive, only a small, discretized portion of the 4π scattering field can be collected from tissue, limiting the amount of information available for diagnostic purposes. In this work, we comprehensively characterize the diagnostic impact of variations in angular sampling, range and noise for inverse light scattering analysis of nuclear morphology, using a previously reported dataset from 40 patients undergoing a/LCI optical biopsy for cervical dysplasia. The results from this analysis are applied to a benchtop scanning a/LCI system which compromises angular range for wide-area scanning capability. This work will inform the design of next-generation optical biopsy probes by directing optical design towards parameters which offer the most diagnostic utility.

Comparison of imaging fiber bundles for coherence-domain imaging

Use of imaging fiber bundles for coherence-domain imaging has remained limited to date. In this work, we provide characterization of commercially available imaging bundles for coherence-domain imaging, by evaluating their modal structure for applicability to interferometric imaging. We further examine custom fabricated bundles developed in collaboration with a corporate partner for their ability to reduce interelement optical path length variability and cross talk between elements. The results presented here will serve as a useful guide for comparing fiber bundles for coherence imaging while also offering an improved understanding of the functionality and limitations of imaging bundles for advancing coherent imaging technologies.

Scanning system for angle-resolved low-coherence interferometry

Angle-resolved low-coherence interferometry (a/LCI) detects precancer by enabling depth-resolved measurements of nuclear morphology in vivo. A significant limitation of a/LCI is the point-probe nature of the method, sampling <0.5  mm² before probe relocation is necessary. In this work, we demonstrate a scanning method capable of assessing an area >100  mm² without repositioning. By utilizing a reflection-only three-optic rotator prism and a two-axis scanning mirror, we demonstrate radial scans of a sample with a linear range of 12 mm and a full rotational range of 180°. Use of this design will improve the diagnostic utility of a/LCI for wide-area screening of tissue health.

Label-Free Classification of Bax/Bak Expressing vs. Double-Knockout Cells

We combine optical scatter imaging with principal component analysis (PCA) to classify apoptosis-competent Bax/Bak-expressing, and apoptosis resistant Bax/Bak-null immortalized baby mouse kidney cells. We apply PCA to 100 stacks each containing 236 dark-field cell images filtered with an optically implemented Gabor filter with period between 0.3 and 2.9 μm. Each stack yields an "eigencell" image corresponding to the first principal component obtained at one of the 100 Gabor filter periods used. At each filter period, each cell image is multiplied by (projected onto) the eigencell image. A Feature Matrix consisting of 236 × 100 scalar values is thus constructed with significantly reduced dimension compared to the initial dataset. Utilizing this Feature Matrix, we implement a supervised linear discriminant analysis and classify successfully the Bax/Bak-expressing and Bax/Bak-null cells with 94.7% accuracy and an area under the curve (AUC) of 0.993. Applying a feature selection algorithm further reveals that the Gabor filter period ranges most significant for the classification correspond to both large (likely nuclear) features as well as small sized features (likely organelles present in the cytoplasm). Our results suggest that cells with a genetic defect in their apoptosis pathway can be differentiated from their normal counterparts by label-free multi-parametric optical scatter data.

Depth-resolved measurements with elliptically polarized reflectance spectroscopy

The ability of elliptical polarized reflectance spectroscopy (EPRS) to detect spectroscopic alterations in tissue mimicking phantoms and in biological tissue in situ is demonstrated. It is shown that there is a linear relationship between light penetration depth and ellipticity. This dependence is used to demonstrate the feasibility of a depth-resolved spectroscopic imaging using EPRS. The advantages and drawbacks of EPRS in evaluation of biological tissue are analyzed and discussed.

Current concepts and future of noninvasive procedures for diagnosing oral squamous cell carcinoma--a systematic review

Background

Oral squamous cell carcinoma (OSCC) has a remarkably high incidence worldwide, and a fairly serious prognosis, encouraging further research into advanced technologies for noninvasive methods of making early diagnoses, ideally in primary care settings.

Objectives

Our purpose was to examine the validity of using advanced noninvasive technologies in diagnosis of OSCC by identifying and evaluating relevant published reports.

Data source

MEDLINE, EMBASE, and CINAHL were searched to identify clinical trials and other information published between 1990 and 10 June 2014; the searches of MEDLINE and EMBASE were updated to November 2014. Study selection: Studies of noninvasive methods of diagnosing OSCC, including oral brush biopsy, optical biopsy, saliva-based oral cancer diagnosis, and others were included.

Data extraction

Data were abstracted and evaluated in duplicate for possible relevance on two occasions at an interval of 2 months before being included or excluded.

Data synthesis

This study identified 163 studies of noninvasive methods for diagnosing OSCC that met the inclusion criteria. These included six studies of oral brush biopsy, 42 of saliva-based oral diagnosis, and 115 of optical biopsy. Sixty nine of these studies were assessed by the modified version of the QUADAS instrument. Saliva-based oral cancer diagnosis and optical biopsy were found to be promising noninvasive methods for diagnosing OSCC.

Limitation

The strength of evidence was rated low for accuracy outcomes because the studies did not report important details required to assess the risk for bias.

Conclusions

It is clear that screening for and early detection of cancer and pre-cancerous lesions have the potential to reduce the morbidity and mortality of this disease. Advances in technologies for saliva-based oral diagnosis and optical biopsy are promising pathways for the future development of more effective noninvasive methods for diagnosing OSCC that are easy to perform clinically in primary care settings.

Emerging enhanced imaging technologies of the esophagus: spectroscopy, confocal laser endomicroscopy, and optical coherence tomography

BACKGROUND

Despite advances in diagnoses and therapy, esophageal adenocarcinoma remains a highly lethal neoplasm. Hence, a great interest has been placed in detecting early lesions and in the detection of Barrett esophagus (BE). Advanced imaging technologies of the esophagus have then been developed with the aim of improving biopsy sensitivity and detection of preplastic and neoplastic cells. The purpose of this article was to review emerging imaging technologies for esophageal pathology, spectroscopy, confocal laser endomicroscopy (CLE), and optical coherence tomography (OCT).

METHODS

We conducted a PubMed search using the search string "esophagus or esophageal or oesophageal or oesophagus" and "Barrett or esophageal neoplasm" and "spectroscopy or optical spectroscopy" and "confocal laser endomicroscopy" and "confocal microscopy" and "optical coherence tomography." The first and senior author separately reviewed all articles. Our search identified: 19 in vivo studies with spectroscopy that accounted for 1021 patients and 4 ex vivo studies; 14 clinical CLE in vivo studies that accounted for 941 patients and 1 ex vivo study with 13 patients; and 17 clinical OCT in vivo studies that accounted for 773 patients and 2 ex vivo studies.

RESULTS

Human studies using spectroscopy had a very high sensitivity and specificity for the detection of BE. CLE showed a high interobserver agreement in diagnosing esophageal pathology and an accuracy of predicting neoplasia. We also found several clinical studies that reported excellent diagnostic sensitivity and specificity for the detection of BE using OCT.

CONCLUSIONS

Advanced imaging technology for the detection of esophageal lesions is a promising field that aims to improve the detection of early esophageal lesions. Although advancing imaging techniques improve diagnostic sensitivities and specificities, their integration into diagnostic protocols has yet to be perfected.

Advances in optical adjunctive AIDS for visualisation and detection of oral malignant and potentially malignant lesions

Traditional methods of screening for oral potentially malignant disorders and oral malignancies involve a conventional oral examination with digital palpation. Evidence indicates that conventional examination is a poor discriminator of oral mucosal lesions. A number of optical aids have been developed to assist the clinician to detect oral mucosal abnormalities and to differentiate benign lesions from sinister pathology. This paper discusses advances in optical technologies designed for the detection of oral mucosal abnormalities. The literature regarding such devices, VELscope and Identafi, is critically analysed, and the novel use of Narrow Band Imaging within the oral cavity is also discussed. Optical aids are effective in assisting with the detection of oral mucosal abnormalities; however, further research is required to evaluate the usefulness of these devices in differentiating benign lesions from potentially malignant and malignant lesions.

Method of detecting tissue contact for fiber-optic probes to automate data acquisition without hardware modification

We present a novel algorithm to detect contact with tissue and automate data acquisition. Contact fiber-optic probe systems are useful in noninvasive applications and real-time analysis of tissue properties. However, applications of these technologies are limited to procedures with visualization to ensure probe-tissue contact and individual user techniques can introduce variability. The software design exploits the system previously designed by our group as an optical method to automatically detect tissue contact and trigger acquisition. This method detected tissue contact with 91% accuracy, detected removal from tissue with 83% accuracy and reduced user variability by > 8%. Without the need for additional hardware, this software algorithm can easily integrate into any fiber-optic system and expands applications where visualization is difficult.