Cellular resolution ex vivo imaging of gastrointestinal tissues with optical coherence microscopy

Digital aberration correction enhances field of view in visible-light optical coherence microscopy

In optical coherence microscopy, optical aberrations commonly result in astigmatism-dominated wavefront errors in the peripheral regions of the optical objective, primarily elongating the microscope's point-spread function along the radial direction in the vicinity of the focal plane. We report on enhanced-field-of-view optical coherence microscopy through computational aberration correction in the visible-light range. An isotropic spatial resolution of 2.5 µm was achieved over an enhanced lateral field of view spanning 1.3 mm × 1.6 mm, as experimentally verified in a micro-bead phantom and further demonstrated in ex vivo tissue samples. The extended field of view achieved by the digital aberration correction facilitates the use of low-cost systems by averting the need for high-quality objectives.

Spectroscopic thermo-elastic optical coherence tomography for tissue characterization

Optical imaging techniques that provide free space, label free imaging are powerful tools in obtaining structural and biochemical information in biological samples. To date, most of the optical imaging technologies create images with a specific contrast and require multimodality integration to add additional contrast. In this study, we demonstrate spectroscopic Thermo-elastic Optical Coherence Tomography (TE-OCT) as a potential tool in tissue identification. TE-OCT creates images based on two different forms of contrast: optical reflectance and thermo-elastic deformation. TE-OCT uses short laser pulses to induce thermo-elastic tissue deformation and measures the resulting surface displacement using phase-sensitive OCT. In this work we characterized the relation between thermo-elastic displacement and optical absorption, excitation, fluence and illumination area. The experimental results were validated with a 2-dimensional analytical model. Using spectroscopic TE-OCT, the thermo-elastic spectra of elastic phantoms and tissue components in coronary arteries were extracted. Specific tissue components, particularly lipid, an important biomarker for identifying atherosclerotic lesions, can be identified in the TE-OCT spectral response. As a label-free, free-space, dual-contrast, all-optical imaging technique, spectroscopic TE-OCT holds promise for biomedical research and clinical pathology diagnosis.

Differentiation between normal and tumor mammary glands with depth-resolved attenuation coefficient from optical coherence tomography

Optical coherence tomography (OCT) is a well-established imaging technology for high-resolution, cross-sectional imaging of biological tissues. Imaging processing and light attenuation coefficient estimation allows to further improve the OCT diagnostic capability. In this paper we use a commercial OCT system, Telesto II-1325LR from Thorlabs, and demonstrate its ability to differentiate normal and tumor mammary mouse glands with the OCT attenuation coefficient. Using several OCT images of normal and tumor mammary mouse glands (n = 26), a statistical analysis was performed. The attenuation coefficient was calculated in depth, considering a slope of 0.5 mm. The normal glands present a median attenuation coefficient of 0.403 mm^-1, comparatively to 0.561 mm^-1obtained for tumor mammary glands. This translates in an attenuation coefficient approximately 39% higher for tumor mammary glands when compared to normal mammary glands. The OCT attenuation coefficient estimation eliminates the subjective analysis provided by direct visualization of the OCT images.

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.

Moxifloxacin based fluorescence imaging of intestinal goblet cells

Goblet cells (GCs) in the intestine are specialized epithelial cells that secrete mucins to form the protective mucous layer. GCs are important in maintaining intestinal homeostasis, and the alteration of GCs is observed in inflammatory bowel diseases (IBDs) and neoplastic lesions. In the Barrett's esophagus, the presence of GCs is used as a marker of specialized intestinal metaplasia. Various endomicroscopic imaging methods have been used for imaging intestinal GCs, but high-speed and high-contrast GC imaging has been still difficult. In this study, we developed a high-contrast endoscopic GC imaging method: fluorescence endomicroscopy using moxifloxacin as a GC labeling agent. Moxifloxacin based fluorescence imaging of GCs was verified by using two-photon microscopy (TPM) in the normal mouse colon. Label-free TPM, which could visualize GCs in a negative contrast, was used as the reference. High-speed GC imaging was demonstrated by using confocal microscopy and endomicroscopy in the normal mouse colon. Confocal microscopy was applied to dextran sulfate sodium (DSS) induced colitis mouse models for the detection of GC depletion. Moxifloxacin based GC imaging was demonstrated not only by 3D microscopies but also by wide-field fluorescence microscopy, and intestinal GCs in the superficial region were imaged. Moxifloxacin based endomicroscopy has a potential for the application to human subjects by using FDA approved moxifloxacin.

Automated imaging cytometry reveals dysplastic indices of colonic serrated adenomas

Aim:

Left-sided colonic serrated adenomas (L-SAs) were evaluated for aneuploidy using automated imaging cytometry to quantify DNA content and compared with normal colonic tissues (NCT), tubular adenomas (TA), left-sided hyperplastic polyps (L-HP) and adenocarcinomas.

Materials & methods:

We used standard paraffin-embedded Feulgen-stained tissue sections.

Results:

The mean DNA index (DI) of NCT was 0.95, L-HP was 1.08, TA was 1.22, L-SA was 1.11 and adenocarcinomas was 1.46. DI of L-SA was statistically higher than that of NCT, but not statistically different from L-HP.

Conclusion:

This study demonstrates that DIs correlate with the described neoplastic progression of L-SA, TA and L-SA compared with NCT and suggests that L-SA may be involved in a chromosome instability pathway of neoplastic progression.

Colon cancer remains a deadly disease, with a significant burden of illness to patients and healthcare systems. While most precursor lesions will not necessarily produce cancers, they vary in histology and potential for neoplastic progression. Aneuploidy or abnormal chromosomal content of a cell is considered a marker for chromosomal instability and neoplastic progression. However, conventional methods of assessment can be laborious, costly and may even underestimate its malignant potential if the lesion is focal, small and surrounded by normal stromal cells in the sampled tissue. We used a nuclear stain to detect and quantify aneuploidy on conventionally prepared colonic precancerous histological slides and in particular assessed serrated and hyperplastic polyps of the left colon. When compared with normal tissues, we determined that there was aneuploidy in these lesions, which supports the underappreciated assumption that these lesions manifest chromosomal instability.

Understanding optical reflectance contrast for real-time characterization of epithelial precursor lesions

Detecting early-stage epithelial cancers and their precursor lesions are challenging as lesions could be subtle and focally or heterogeneously distributed over large mucosal areas. Optical coherence tomography (OCT) that enables wide-field imaging of subsurface microstructures in vivo is a promising screening tool for epithelial diseases. However, its diagnostic capability has not been fully appreciated since the optical reflectance contrast is poorly understood. We investigated the back-scattered intensities from clustered or packed nanometer scale intracellular scatterers using finite-difference time-domain method and 1-μm resolution form of OCT, and uncovered that there existed correlations between the reflectance contrasts and the ultrastructural clustering or packing states of these scatterers, which allows us to interpret the physiological state of the cells. Specifically, both polarized goblet cells and foveolar cells exhibited asymmetric reflectance contrast, but they could be differentiated by the optical intensity of the mucin cup due to the different ultrastructural make-ups of the mucin granules; keratinocytes could demonstrate varied cytoplasmic intensity and their cytoplasmic contrast was closely correlated with the packing state of keratin filaments. Further preliminary study demonstrated that these new understandings of OCT image contrast enables the characterization of precancerous lesions, which could complement the current morphology-based criteria in realizing "virtual histology" and would have a profound impact for the screening and surveillance of epithelial cancers.

Volumetric laser endomicroscopy and optical coherence tomography in Barrett's esophagus: a systematic review and meta-analysis

Background and study aims  Endoscopic imaging of Barrett's esophagus (BE) with advanced technologies, such as optical coherence tomography (OCT) and volumetric laser endomicroscopy (VLE), allows targeted biopsies and may reduce the number of random biopsies to detect esophageal neoplasia in the early stages during endoscopic BE surveillance. The aim of this study was to evaluate the accuracy of OCT and VLE in diagnosis of intestinal metaplasia, dysplasia, and high-grade dysplasia (HGD), and intramucosal carcinoma (IMC) in BE. Patients and methods  In this systematic review and meta-analysis, the primary outcome measure was diagnostic accuracy of OCT and VLE, in comparison with the gold standard. In the meta-analysis, we calculated sensitivity, specificity, positive likelihood ratio (LR+), negative likelihood ratio (LR-), and diagnostic odds ratio (DOR) for both methods. We performed analyses by patient and by lesion. Results  We evaluated 14 studies involving a collective total of 721 patients and 1565 lesions. In the analysis by lesion, VLE showed a pooled sensitivity, specificity, LR+, LR-, DOR, and SROC AUC of 85 %, 73 %, 3.2, 0.21, 15.0, and 0.87, respectively, for detection of HGD/IMC. In the analysis by lesion for detection of HGD/EAC, OCT showed a pooled sensitivity, specificity, LR+, LR-, DOR, and summary receiver operating characteristic area under the curve of 89 %, 91 %, 9.6, 0.12, 81.0, and 0.95, respectively. The accuracy of OCT in identifying intestinal metaplasia showed a pooled sensitivity, specificity, LR+, LR-, and DOR of 92 %, 81 %, 5.06, 0.091, and 55.58, respectively. Conclusion  OCT- and VLE-guided targeted biopsies could improve detection of dysplasia and neoplasia. Further studies could determine whether the use of such biopsies might replace the current protocol.

High-spatial-resolution deep tissue imaging with spectral-domain optical coherence microscopy in the 1700-nm spectral band

We present three-dimensional (3-D) high-resolution spectral-domain optical coherence microscopy (SD-OCM) by using a supercontinuum (SC) fiber laser source with 300-nm spectral bandwidth (full-width at half-maximum) in the 1700-nm spectral band. By using low-coherence interferometry with SC light and a confocal detection scheme, we realized lateral and axial resolutions of 3.4 and 3.8  μm in tissue (n  =  1.38), respectively. This is, to the best of our knowledge, the highest 3-D spatial resolution reported among those of Fourier-domain optical coherence imaging techniques in the 1700-nm spectral band. In our SD-OCM, to enhance the imaging depth, a full-range method was implemented, which suppressed the formation of a coherent ghost image and allowed us to set the zero-delay position inside the samples. We demonstrated the 3-D high-resolution imaging capability of 1700-nm SD-OCM through the measurement of an interference signal from a mirror surface and imaging of a single 200-nm polystyrene bead and a pig thyroid gland. Deep tissue imaging at a depth of up to 1.8 mm was also demonstrated. This is the first demonstration of 3-D high-resolution SD-OCM in the 1700-nm spectral band.

Review of optical coherence tomography in oncology

The application of optical coherence tomography (OCT) in the field of oncology has been prospering over the past decade. OCT imaging has been used to image a broad spectrum of malignancies, including those arising in the breast, brain, bladder, the gastrointestinal, respiratory, and reproductive tracts, the skin, and oral cavity, among others. OCT imaging has initially been applied for guiding biopsies, for intraoperatively evaluating tumor margins and lymph nodes, and for the early detection of small lesions that would often not be visible on gross examination, tasks that align well with the clinical emphasis on early detection and intervention. Recently, OCT imaging has been explored for imaging tumor cells and their dynamics, and for the monitoring of tumor responses to treatments. This paper reviews the evolution of OCT technologies for the clinical application of OCT in surgical and noninvasive interventional oncology procedures and concludes with a discussion of the future directions for OCT technologies, with particular emphasis on their applications in oncology.

Integrated local binary pattern texture features for classification of breast tissue imaged by optical coherence microscopy

This paper proposes a texture analysis technique that can effectively classify different types of human breast tissue imaged by Optical Coherence Microscopy (OCM). OCM is an emerging imaging modality for rapid tissue screening and has the potential to provide high resolution microscopic images that approach those of histology. OCM images, acquired without tissue staining, however, pose unique challenges to image analysis and pattern classification. We examined multiple types of texture features and found Local Binary Pattern (LBP) features to perform better in classifying tissues imaged by OCM. In order to improve classification accuracy, we propose novel variants of LBP features, namely average LBP (ALBP) and block based LBP (BLBP). Compared with the classic LBP feature, ALBP and BLBP features provide an enhanced encoding of the texture structure in a local neighborhood by looking at intensity differences among neighboring pixels and among certain blocks of pixels in the neighborhood. Fourty-six freshly excised human breast tissue samples, including 27 benign (e.g. fibroadenoma, fibrocystic disease and usual ductal hyperplasia) and 19 breast carcinoma (e.g. invasive ductal carcinoma, ductal carcinoma in situ and lobular carcinoma in situ) were imaged with large field OCM with an imaging area of 10 × 10 mm² (10, 000 × 10, 000 pixels) for each sample. Corresponding H&E histology was obtained for each sample and used to provide ground truth diagnosis. 4310 small OCM image blocks (500 × 500 pixels) each paired with corresponding H&E histology was extracted from large-field OCM images and labeled with one of the five different classes: adipose tissue (n = 347), fibrous stroma (n = 2,065), breast lobules (n = 199), carcinomas (pooled from all sub-types, n = 1,127), and background (regions outside of the specimens, n = 572). Our experiments show that by integrating a selected set of LBP and the two new variant (ALBP and BLBP) features at multiple scales, the classification accuracy increased from 81.7% (using LBP features alone) to 93.8% using a neural network classifier. The integrated feature was also used to classify large-field OCM images for tumor detection. A receiver operating characteristic (ROC) curve was obtained with an area under the curve value of 0.959. A sensitivity level of 100% and specificity level of 85.2% was achieved to differentiate benign from malignant samples. Several other experiments also demonstrate the complementary nature of LBP and the two variants (ALBP and BLBP features) and the significance of integrating these texture features for classification. Using features from multiple scales and performing feature selection are also effective mechanisms to improve accuracy while maintaining computational efficiency.

Optical coherence microscopy in 1700 nm spectral band for high-resolution label-free deep-tissue imaging

Optical coherence microscopy (OCM) is a label-free, high-resolution, three-dimensional (3D) imaging technique based on optical coherence tomography (OCT) and confocal microscopy. Here, we report that the 1700-nm spectral band has the great potential to improve the imaging depth in high-resolution OCM imaging of animal tissues. Recent studies to improve the imaging depth in OCT revealed that the 1700-nm spectral band is a promising choice for imaging turbid scattering tissues due to the low attenuation of light in the wavelength region. In this study, we developed high-resolution OCM by using a high-power supercontinuum source in the 1700-nm spectral band, and compared the attenuation of signal-to-noise ratio between the 1700-nm and 1300-nm OCM imaging of a mouse brain under the condition of the same sensitivity. The comparison clearly showed that the 1700-nm OCM provides larger imaging depth than the 1300-nm OCM. In this 1700-nm OCM, the lateral resolution of 1.3 μm and the axial resolution of 2.8 μm, when a refractive index was assumed to be 1.38, was achieved.

Preliminary study of optical coherence tomography imaging to identify microscopic extrathyroidal extension in patients with papillary thyroid carcinoma

BACKGROUND AND OBJECTIVES

We evaluated the feasibility of using optical coherence tomography (OCT), to identify microscopic extrathyroidal extension (mETE) in ex vivo thyroidectomy specimens of patients who underwent thyroidectomy for the treatment of papillary thyroid carcinoma (PTC).

METHODS

A total of 170 ex vivo OCT images of the tumor, were acquired just after completion of thyroidectomy in 17 patients. The OCT images of each patient were separately evaluated by two blinded investigators, and the outcomes were compared with the histopathology reports.

RESULTS

The sensitivity and specificity of mETE identification from the OCT images were 81.4% and 86.0%, respectively, for the first investigator, and 82.9% and 87.0%, respectively, for the second investigator. Substantial agreement between the investigators was verified by Cohen's κ (Cohen's κ = 0.772).

CONCLUSION

In this preliminary study of a limited series of ex vivo thyroidectomy specimens, we verified the feasibility of OCT as a method of identifying mETE in patients with PTC.

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.

Capturing structure and function in an embryonic heart with biophotonic tools

Disturbed cardiac function at an early stage of development has been shown to correlate with cellular/molecular, structural as well as functional cardiac anomalies at later stages culminating in the congenital heart defects (CHDs) that present at birth. While our knowledge of cellular and molecular steps in cardiac development is growing rapidly, our understanding of the role of cardiovascular function in the embryo is still in an early phase. One reason for the scanty information in this area is that the tools to study early cardiac function are limited. Recently developed and adapted biophotonic tools may overcome some of the challenges of studying the tiny fragile beating heart. In this chapter, we describe and discuss our experience in developing and implementing biophotonic tools to study the role of function in heart development with emphasis on optical coherence tomography (OCT). OCT can be used for detailed structural and functional studies of the tubular and looping embryo heart under physiological conditions. The same heart can be rapidly and quantitatively phenotyped at early and again at later stages using OCT. When combined with other tools such as optical mapping (OM) and optical pacing (OP), OCT has the potential to reveal in spatial and temporal detail the biophysical changes that can impact mechanotransduction pathways. This information may provide better explanations for the etiology of the CHDs when interwoven with our understanding of morphogenesis and the molecular pathways that have been described to be involved. Future directions for advances in the creation and use of biophotonic tools are discussed.

Toward the guidance of transbronchial biopsy: identifying pulmonary nodules with optical coherence tomography

BACKGROUND

Solitary pulmonary nodules (SPNs) frequently require transbronchial needle aspiration (TBNA) or biopsy to determine malignant potential, but have variable diagnostic yields. Confirming needle placement within SPNs during TBNA could significantly increase diagnostic yield. Optical coherence tomography (OCT) provides nondestructive, high-resolution, microstructural imaging with potential to distinguish SPN from parenchyma. We have developed needle-based OCT probes compatible with TBNA. Before OCT can play any significant role in guiding clinical TBNA, OCT interpretation criteria for differentiating SPN from lung parenchyma must be developed and validated.

METHODS

OCT of SPN and parenchyma was performed on 111 ex vivo resection specimens. OCT criteria for parenchyma and SPN were developed and validated in a blinded assessment. Six blinded readers (two pulmonologists, two pathologists, and two OCT experts) were trained on imaging criteria in a 15-min training session prior to interpreting the validation data set.

RESULTS

OCT of lung parenchyma displayed evenly spaced signal-void alveolar spaces, signal-intense backreflections at tissue-air interfaces, or both. SPNs lacked both of these imaging features. Independent validation of OCT criteria by the six blinded readers demonstrated sensitivity and specificity of 95.4% and 98.2%, respectively.

CONCLUSIONS

We have developed and validated OCT criteria for lung parenchyma and SPN with sensitivity and specificity > 95% in this ex vivo study. We anticipate that OCT could be a useful complementary imaging modality to confirm needle placement during TBNA to potentially increase diagnostic yield.

Optical coherence tomography imaging during thyroid and parathyroid surgery: a novel system of tissue identification and differentiation to obviate tissue resection and frozen section

BACKGROUND

Optical coherence tomography (OCT) allows tissue histologic-like evaluation, but without tissue fixation or staining. We investigated OCT images from tissues obtained at thyroid and parathyroid surgeries to provide a preliminary assessment as to whether these images contain sufficient information for recognition and differentiation of normal neck tissues.

METHODS

Normal tissues were obtained from patients undergoing surgical treatment. Two new-generation OCT systems, including optical frequency domain imaging (OFDI) and μOCT, were compared to representative hematoxylin-eosin histology.

RESULTS

Thyroid, fat, muscle, lymph nodes, and parathyroid tissues were evaluated. Histologic-like microscopic characteristics sufficient for tissue type identification was realized using both systems for all tissue types examined.

CONCLUSION

This pilot study demonstrated that new-generation OCT systems are capable of recognizing and differentiating neck tissues encountered during thyroid and parathyroid surgeries. Further advances in OCT miniaturization and development of sterile intraoperative probe formats may allow OCT to offer an intraoperative "optical biopsy" without fixation, staining, or tissue resection.

Swept source optical coherence microscopy using a 1310 nm VCSEL light source

We demonstrate high speed, swept source optical coherence microscopy (OCM) using a MEMS tunable vertical cavity surface-emitting laser (VCSEL) light source. The light source had a sweep rate of 280 kHz, providing a bidirectional axial scan rate of 560 kHz. The sweep bandwidth was 117 nm centered at 1310 nm, corresponding to an axial resolution of 13.1 µm in air, corresponding to 8.1 µm (9.6 µm spectrally shaped) in tissue. Dispersion mismatch from different objectives was compensated numerically, enabling magnification and field of view to be easily changed. OCM images were acquired with transverse resolutions between 0.86 µm - 3.42 µm using interchangeable 40X, 20X and 10X objectives with ~600 µm x 600 µm, ~1 mm x 1 mm and ~2 mm x 2 mm field-of-view (FOV), respectively. Parasitic variations in path length with beam scanning were corrected numerically. These features enable swept source OCM to be integrated with a wide range of existing scanning microscopes. Large FOV mosaics were generated by serially acquiring adjacent overlapping microscopic fields and combining them in post-processing. Fresh human colon, thyroid and kidney specimens were imaged ex vivo and compared to matching histology sections, demonstrating the ability of OCM to image tissue specimens.

Volumetric optical frequency domain imaging of pulmonary pathology with precise correlation to histopathology

BACKGROUND

Lung cancer is the leading cause of cancer-related mortality. Radiology and bronchoscopy techniques do not have the necessary resolution to evaluate lung lesions on the microscopic scale, which is critical for diagnosis. Bronchial biopsy specimens can be limited by sampling error and small size. Optical frequency domain imaging (OFDI) provides volumetric views of tissue microstructure at near-histologic resolution and may be useful for evaluating pulmonary lesions to increase diagnostic accuracy. Bronchoscopic OFDI has been evaluated in vivo, but a lack of correlated histopathology has limited the ability to develop accurate image interpretation criteria.

METHODS

We performed OFDI through two approaches (airway-centered and parenchymal imaging) in 22 ex vivo lung specimens, using tissue dye to precisely correlate imaging and histology.

RESULTS

OFDI of normal airway allowed visualization of epithelium, lamina propria, cartilage, and alveolar attachments. Carcinomas exhibited architectural disarray, loss of normal airway and alveolar structure, and rapid light attenuation. Squamous cell carcinomas showed nested architecture. Atypical glandular formation was appreciated in adenocarcinomas, and uniform trabecular gland formation was seen in salivary gland carcinomas. Mucinous adenocarcinomas showed alveolar wall thickening with intraalveolar mucin. Interstitial fibrosis was visualized as signal-dense tissue, with an interstitial distribution in mild interstitial fibrotic disease and a diffuse subpleural pattern with cystic space formation in usual interstitial pneumonitis.

CONCLUSIONS

To our knowledge, this study is the first demonstration of volumetric OFDI with precise correlation to histopathology in lung pathology. We anticipate that OFDI may play a role in assessing airway and parenchymal pathology, providing fresh insights into the volumetric features of pulmonary disease.

Three-dimensional multiphoton/optical coherence tomography for diagnostic applications in dermatology

A preliminary clinical trial using state-of-the-art multiphoton tomography (MPT) and optical coherence tomography (OCT) for three-dimensional (3D) multimodal in vivo imaging of normal skin, nevi, scars and pathologic skin lesions has been conducted. MPT enabled visualization of sub-cellular details with axial and transverse resolutions of <2 μm and <0.5 μm, respectively, from a volume of 0.35 × 0.35 × 0.2 mm(3) at a frame rate of 0.14 Hz (512 × 512 pixels). State-of-the-art OCT, operating at a center wavelength of 1300 nm, was capable of acquiring 3D images depicting the layered architecture of skin with axial and transverse resolutions ~8 μm and ~20 μm, respectively, from a volume of 7 × 3.5 × 1.5 mm(3) at a frame rate of 46 Hz (1024 × 1024 pixels). This study demonstrates the clinical diagnostic potential of MPT/OCT for pre-screening relatively large areas of skin using 3D OCT to identify suspicious regions at microscopic level and subsequently using high resolution MPT to obtain zoomed in, sub-cellular level information of the respective regions.

Ultrahigh speed spectral-domain optical coherence microscopy

We demonstrate a compact, ultrahigh speed spectral-domain optical coherence microscopy (SD-OCM) system for multiscale imaging of specimens at 840 nm. Using a high speed 512-pixel line scan camera, an imaging speed of 210,000 A-scans per second was demonstrated. Interchangeable water immersion objectives with magnifications of 10×, 20×, and 40× provided co-registered en face cellular-resolution imaging over several size scales. Volumetric OCM data sets and en face OCM images were demonstrated on both normal and pathological human colon and kidney specimens ex vivo with an axial resolution of ~4.2 µm, and transverse resolutions of ~2.9 µm (10×), ~1.7 µm (20×), and ~1.1 µm (40×) in tissue. In addition, en face OCM images acquired with high numerical aperture over an extended field-of-view (FOV) were demonstrated using image mosaicking. Comparison between en face OCM images among different transverse and axial resolutions was demonstrated, which promises to help the design and evaluation of imaging performance of Fourier domain OCM systems at different resolution regimes.

Review of advanced imaging techniques

Pathology informatics encompasses digital imaging and related applications. Several specialized microscopy techniques have emerged which permit the acquisition of digital images (“optical biopsies”) at high resolution. Coupled with fiber-optic and micro-optic components, some of these imaging techniques (e.g., optical coherence tomography) are now integrated with a wide range of imaging devices such as endoscopes, laparoscopes, catheters, and needles that enable imaging inside the body. These advanced imaging modalities have exciting diagnostic potential and introduce new opportunities in pathology. Therefore, it is important that pathology informaticists understand these advanced imaging techniques and the impact they have on pathology. This paper reviews several recently developed microscopic techniques, including diffraction-limited methods (e.g., confocal microscopy, 2-photon microscopy, 4Pi microscopy, and spatially modulated illumination microscopy) and subdiffraction techniques (e.g., photoactivated localization microscopy, stochastic optical reconstruction microscopy, and stimulated emission depletion microscopy). This article serves as a primer for pathology informaticists, highlighting the fundamentals and applications of advanced optical imaging techniques.

Improved Detection Sensitivity of Line-Scanning Optical Coherence Microscopy

Optical coherence microscopy (OCM) is a promising technology for high-resolution cellular-level imaging in human tissues. Line-scanning OCM is a new form of OCM that utilizes line-field illumination for parallel detection. In this study, we demonstrate improved detection sensitivity by using an achromatic design for line-field generation. This system operates at 830-nm wavelength with 82-nm bandwidth. The measured axial resolution is 3.9 μm in air (corresponding to ~2.9 μm in tissue), and the transverse resolutions are 2.1 μm along the line-field illumination direction and 1.7 μm perpendicular to line illumination direction. The measured sensitivity is 98 dB with 25 line averages, resulting in an imaging speed of ~2 frames/s (516 lines/s). Real-time, cellular-level imaging of scattering tissues is demonstrated using human-colon specimens.

Integrated optical coherence tomography and optical coherence microscopy imaging of ex vivo human renal tissues

PURPOSE

We evaluated the feasibility of using optical coherence tomography and optical coherence microscopy technology to assess human kidney morphology.

MATERIALS AND METHODS

A total of 35 renal specimens from 19 patients, consisting of 12 normal tissues and 23 tumors (16 clear cell renal cell carcinomas, 5 papillary renal cell carcinomas and 2 oncocytomas) were imaged ex vivo after surgical resection. Optical coherence tomography and optical coherence microscopy images were compared to corresponding hematoxylin and eosin histology to identify characteristic features of normal and pathological renal tissues. Three pathologists blinded to histology evaluated the sensitivity and specificity of optical coherence microscopy images to differentiate normal from neoplastic renal tissues.

RESULTS

Optical coherence tomography and optical coherence microscopy images of normal kidney revealed architectural features, including glomeruli, convoluted tubules, collecting tubules and loops of Henle. Each method of imaging renal tumors clearly demonstrated morphological changes and decreased imaging depth. Optical coherence tomography and microscopy features matched well with the corresponding histology. Three observers achieved 88%, 100% and 100% sensitivity, and 100%, 88% and 100% specificity, respectively, when evaluating normal vs neoplastic specimens using optical coherence microscopy images with substantial interobserver agreement (κ = 0.82, p <0.01).

CONCLUSIONS

Integrated optical coherence tomography and optical coherence microscopy imaging provides coregistered, multiscale images of renal pathology in real time without exogenous contrast medium or histological processing. High sensitivity and specificity were achieved using optical coherence microscopy to differentiate normal from neoplastic renal tissues, suggesting possible applications for guiding renal mass biopsy or evaluating surgical margins.

Multiscale multimodal imaging with multiphoton microscopy and optical coherence tomography

A multiscale multiphoton microscopy (MPM) and optical coherence tomography (OCT) system has been developed using a sub-10 fs Ti:sapphire laser. The system performs cross-sectional OCT imaging over millimeter field-of-view and en-face high-resolution MPM imaging with submicrometer resolution from the same sample location. With fish cornea, we have demonstrated cross-sectional imaging of cornea tissue layers using OCT, and the zoom-in imaging of cells and collagen fibers in each layer using MPM. The multiscale MPM/OCT system shows the potential of a rapid coarse scan to search for abnormal regions and the subsequent fine zoom-in imaging for diagnosis.

Quantitative imaging of cochlear soft tissues in wild-type and hearing-impaired transgenic mice by spectral domain optical coherence tomography

Human hearing loss often occurs as a result of damage or malformations to the functional soft tissues within the cochlea, but these changes are not appreciable with current medical imaging modalities. We sought to determine whether optical coherence tomography (OCT) could assess the soft tissue structures relevant to hearing using mouse models. We imaged excised cochleae with an altered tectorial membrane and during normal development. The soft tissue structures and expected anatomical variations were visible using OCT, and quantitative measurements confirmed the ability to detect critical changes relevant to hearing.

Combined two-photon microscopy and optical coherence tomography using individually optimized sources

The combination of two-photon microscopy (TPM) and optical coherence tomography (OCT) is useful in conducting in-vivo tissue studies, because they provide complementary information regarding tissues. In the present study, we developed a new combined system using separate light sources and scanners for individually optimal imaging conditions. TPM used a Ti-Sapphire laser and provided molecular and cellular information in microscopic tissue regions. Meanwhile, OCT used a wavelength-swept source centered at 1300 nm and provided structural information in larger tissue regions than TPM. The system was designed to do simultaneous imaging by combining light from both sources. TPM and OCT had the field of view values of 300 μm and 800 μm on one side respectively with a 20x objective. TPM had resolutions of 0.47 μm and 2.5 μm in the lateral and axial directions respectively, and an imaging speed of 40 frames/s. OCT had resolutions of 5 μm and 8 μm in lateral and axial directions respectively, a sensitivity of 97dB, and an imaging speed of 0.8 volumes per second. This combined system was tested with simple microsphere specimens, and was then applied to image small intestine and ear tissues of mouse models ex-vivo. Molecular, cellular, and structural information of the tissues were visualized using the proposed combined system.

Integrated optical coherence tomography and microscopy for ex vivo multiscale evaluation of human breast tissues

Three-dimensional (3D) tissue imaging methods are expected to improve surgical management of cancer. In this study, we examined the feasibility of two 3D imaging technologies, optical coherence tomography (OCT) and optical coherence microscopy (OCM), to view human breast specimens based on intrinsic optical contrast. Specifically, we imaged 44 ex vivo breast specimens including 34 benign and 10 malignant lesions with an integrated OCT and OCM system developed in our laboratory. The system enabled 4-μm axial resolution (OCT and OCM) with 14-μm (OCT) and 2-μm (OCM) transverse resolutions, respectively. OCT and OCM images were compared with corresponding histologic sections to identify characteristic features from benign and malignant breast lesions at multiple resolution scales. OCT and OCM provide complimentary information about tissue microstructure, thus showing distinctive patterns for adipose tissue, fibrous stroma, breast lobules and ducts, cysts and microcysts, as well as in situ and invasive carcinomas. The 3D imaging capability of OCT and OCM provided complementary information to individual 2D images, thereby allowing tracking features from different levels to identify low-contrast structures that were difficult to appreciate from single images alone. Our results lay the foundation for future in vivo optical evaluation of breast tissues, using OCT and OCM, which has the potential to guide core needle biopsies, assess surgical margins, and evaluate nodal involvement in breast cancer.