Seeing beyond the bronchoscope to increase the diagnostic yield of bronchoscopic biopsy

Assessing Lung Fibrosis with ML-Assisted Minimally Invasive OCT Imaging

This paper presents a combined optical coherence tomography (OCT) imaging/machine learning (ML) technique for real-time analysis of lung tissue morphology to determine the presence and level of invasiveness of idiopathic lung fibrosis (ILF). This is an important clinical problem as misdiagnosis is common, resulting in patient exposure to costly and invasive procedures and substantial use of healthcare resources. Therefore, biopsy is needed to confirm or rule out radiological findings. Videoscopic-assisted thoracoscopic wedge biopsy (VATS) under general anesthesia is typically necessary to obtain enough tissue to make an accurate diagnosis. This kind of biopsy involves the placement of several tubes through the chest wall, one of which is used to cut off a piece of lung to send for evaluation. The removed tissue is examined histopathologically by microscopy to confirm the presence and the pattern of fibrosis. However, VATS pulmonary biopsy can have multiple side effects, including inflammation, tissue morbidity, and severe bleeding, which further degrade the quality of life for the patient. Furthermore, the results are not immediately available, requiring tissue processing and analysis. Here, we report an initial attempt of using ML-assisted polarization sensitive OCT (PS-OCT) imaging for lung fibrosis assessment. This approach has been preliminarily tested on a rat model of lung fibrosis. Our preliminary results show that ML-assisted PS-OCT imaging can detect the presence of ILF with an average of 77% accuracy and 89% specificity.

Intraoperative application of optical coherence tomography for lung tumor

On-site instant determination of benign or malignant tumors for deciding the types of resection is crucial during pulmonary surgery. We designed a portable spectral-domain optical coherence tomography (SD-OCT) system to do real-time scanning intraoperatively for the distinction of fresh tumor specimens in the lung. A total of 12 ex vivo lung specimens from six patients were enrolled. Three patients were diagnosed with invasive adenocarcinoma (IA), while the others were benign. After OCT-imaged reconstruction, we compared the qualitative morphology of OCT and histology among malignant, benign, and normal tissues. In addition, through analysis of the quantitative data, a discrete difference in optical attenuation coefficients around the junctional surface was shown by our data processing. This study demonstrated a feasible OCT-assisted resection guide by a rapid on-site tumor diagnosis. The results indicate that future deep learning of OCT-captured image systems able to improve diagnostic and therapeutic efficiency is warranted.

Advances in bronchoscopic optical coherence tomography and confocal laser endomicroscopy in pulmonary diseases

PURPOSE OF REVIEW

Imaging techniques play a crucial role in the diagnostic work-up of pulmonary diseases but generally lack detailed information on a microscopic level. Optical coherence tomography (OCT) and confocal laser endomicroscopy (CLE) are imaging techniques which provide microscopic images in vivo during bronchoscopy. The purpose of this review is to describe recent advancements in the use of bronchoscopic OCT- and CLE-imaging in pulmonary medicine.

RECENT FINDINGS

In recent years, OCT- and CLE-imaging have been evaluated in a wide variety of pulmonary diseases and demonstrated to be complementary to bronchoscopy for real-time, near-histological imaging. Several pulmonary compartments were visualized and characteristic patterns for disease were identified. In thoracic malignancy, OCT- and CLE-imaging can provide characterization of malignant tissue with the ability to identify the optimal sampling area. In interstitial lung disease (ILD), fibrotic patterns were detected by both (PS-) OCT and CLE, complementary to current HRCT-imaging. For obstructive lung diseases, (PS-) OCT enables to detect airway wall structures and remodelling, including changes in the airway smooth muscle and extracellular matrix.

SUMMARY

Bronchoscopic OCT- and CLE-imaging allow high resolution imaging of airways, lung parenchyma, pleura, lung tumours and mediastinal lymph nodes. Although investigational at the moment, promising clinical applications are on the horizon.

Novel image features of optical coherence tomography for pathological classification of lung cancer: Results from a prospective clinical trial

Background

This study aimed to explore the characteristics of optical coherence tomography (OCT) imaging for differentiating between benign and malignant lesions and different pathological types of lung cancer in bronchial lesions and to preliminarily evaluate the clinical value of OCT.

Methods

Patients who underwent bronchoscopy biopsy and OCT between February 2019 and December 2019 at the Chinese PLA General Hospital were enrolled in this study. White-light bronchoscopy (WLB), auto-fluorescence bronchoscopy (AFB), and OCT were performed at the lesion location. The main characteristics of OCT imaging for the differentiation between benign and malignant lesions and the prediction of the pathological classification of lung cancer in bronchial lesions were identified, and their clinical value was evaluated.

Results

A total of 135 patients were included in this study. The accuracy of OCT imaging for differentiating between benign and malignant bronchial lesions was 94.1%, which was significantly higher than that of AFB (67.4%). For the OCT imaging of SCC, adenocarcinoma, and small-cell lung cancer, the accuracies were 95.6, 94.3, and 92%, respectively. The accuracy, sensitivity, and specificity of OCT were higher than those of WLB. In addition, these main OCT image characteristics are independent influencing factors for predicting the corresponding diseases through logistic regression analysis between the main OCT image characteristics in the study and the general clinical features of patients (p<0.05).

Conclusion

As a non-biopsy technique, OCT can be used to improve the diagnosis rate of lung cancer and promote the development of non-invasive histological biopsy.

Polarization mode dispersion correction in endoscopic polarization-sensitive optical coherence tomography with incoherent polarization input states

The incorporation of polarization sensitivity into optical coherence tomography (PS-OCT) imaging can greatly enhance utility by allowing differentiation via intrinsic contrast of many types of tissue. In fiber-based OCT systems such as those employing endoscopic imaging probes, however, polarization mode dispersion (PMD) can significantly impact the ability to obtain accurate polarization data unless valuable axial resolution is sacrificed. In this work we present a new technique for compensating for PMD in endoscopic PS-OCT with minimal impact on axial resolution and without requiring mutually coherent polarization inputs, needing only a birefringent structure with known orientation in view (such as the catheter sheath). We then demonstrate the advantages of this technique by comparing it against the current state of the art approach.

Polarization Sensitive Imaging with Qubits

We compare reconstructed quantum state images of a birefringent sample using direct quantum state tomography and inverse numerical optimization technique. Qubits are used to characterize birefringence in a flat transparent plastic sample by means of polarization sensitive measurement using density matrices of two-level quantum entangled photons. Pairs of entangled photons are generated in a type-II nonlinear crystal. About half of the generated photons interact with a birefringent sample, and coincidence counts are recorded. Coincidence rates of entangled photons are measured for a set of sixteen polarization states. Tomographic and inverse numerical techniques are used to reconstruct the density matrix, the degree of entanglement, and concurrence for each pixel of the investigated sample. An inverse numerical optimization technique is used to obtain a density matrix from measured coincidence counts with the maximum probability. Presented results highlight the experimental noise reduction, greater density matrix estimation, and overall image enhancement. The outcome of the entanglement distillation through projective measurements is a superposition of Bell states with different amplitudes. These changes are used to characterize the birefringence of a 3M tape. Well-defined concurrence and entanglement images of the birefringence are presented. Our results show that inverse numerical techniques improve overall image quality and detail resolution. The technique described in this work has many potential applications.

Optical coherence tomography

Optical coherence tomography (OCT) is a non-contact method for imaging the topological and internal microstructure of samples in three dimensions. OCT can be configured as a conventional microscope, as an ophthalmic scanner, or using endoscopes and small diameter catheters for accessing internal biological organs. In this Primer, we describe the principles underpinning the different instrument configurations that are tailored to distinct imaging applications and explain the origin of signal, based on light scattering and propagation. Although OCT has been used for imaging inanimate objects, we focus our discussion on biological and medical imaging. We examine the signal processing methods and algorithms that make OCT exquisitely sensitive to reflections as weak as just a few photons and that reveal functional information in addition to structure. Image processing, display and interpretation, which are all critical for effective biomedical imaging, are discussed in the context of specific applications. Finally, we consider image artifacts and limitations that commonly arise and reflect on future advances and opportunities.

Polarization-sensitive optical coherence tomography in end-stage lung diseases: an ex vivo pilot study

A non-invasive diagnostic tool to assess remodeling of the lung airways caused by disease is currently missing in the clinic. Measuring key features such as airway smooth muscle (ASM) thickness would increase the ability to improve diagnosis and enable treatment evaluation. In this research, polarization-sensitive optical coherence tomography (PS-OCT) has been used to image a total of 24 airways from two healthy lungs and four end-stage diseased lungs ex vivo, including fibrotic sarcoidosis, chronic obstructive pulmonary disease (COPD), fibrotic hypersensitivity pneumonitis, and cystic fibrosis. In the diseased lungs, except COPD, the amount of measured airway smooth muscle was increased. In COPD, airway smooth muscle could not be distinguished from surrounding collagen. COPD lungs showed increased alveolar size. 3D pullbacks in the same lumen provided reproducible assessment of airway smooth muscle (ASM). Image features such as thickened ASM and size/presence of alveoli were recognized in histology. The results of this study are preliminary and must be confirmed with further ex vivo and in vivo studies. PS-OCT is applicable for in vivo assessment of peribronchial and peribronchiolar lung structures and may become a valuable tool for diagnosis in pulmonology.

Rapid non-destructive volumetric tumor yield assessment in fresh lung core needle biopsies using polarization sensitive optical coherence tomography

Adequate tumor yield in core-needle biopsy (CNB) specimens is essential in lung cancer for accurate histological diagnosis, molecular testing for therapeutic decision-making, and tumor biobanking for research. Insufficient tumor sampling in CNB is common, primarily due to inadvertent sampling of tumor-associated fibrosis or atelectatic lung, leading to repeat procedures and delayed diagnosis. Currently, there is no method for rapid, non-destructive intraprocedural assessment of CNBs. Polarization-sensitive optical coherence tomography (PS-OCT) is a high-resolution, volumetric imaging technique that has the potential to meet this clinical need. PS-OCT detects endogenous tissue properties, including birefringence from collagen, and degree of polarization uniformity (DOPU) indicative of tissue depolarization. Here, PS-OCT birefringence and DOPU measurements were used to quantify the amount of tumor, fibrosis, and normal lung parenchyma in 42 fresh, intact lung CNB specimens. PS-OCT results were compared to and validated against matched histology in a blinded assessment. Linear regression analysis showed strong correlations between PS-OCT and matched histology for quantification of tumors, fibrosis, and normal lung parenchyma in CNBs. PS-OCT distinguished CNBs with low tumor content from those with higher tumor content with high sensitivity and specificity. This study demonstrates the potential of PS-OCT as a method for rapid, non-destructive, label-free intra-procedural tumor yield assessment.

Examination of a Chinese-made cryptococcal glucuronoxylomannan antigen test in serum and bronchoalveolar lavage fluid for diagnosing pulmonary cryptococcosis in HIV-negative patients

BACKGROUND

We presented the performance of a Chinese-made cryptococcal glucuronoxylomannan (GXM) antigen test using serum and bronchoalveolar lavage fluid (BALF) samples in the HIV-negative Chinese population.

METHODS

Between February 2017 and January 2019, HIV-negative patients with pulmonary cryptococcosis were recruited and followed-up every three months, including completion of a chest CT examination and collection of serum and BALF samples.

RESULTS

Here, thirty-seven confirmed and ten clinically diagnosed patients were recruited. Furthermore, samples from 174 noncryptococcosis patients that may cause false positives were also collected. The sensitivity of a lateral flow assay (LFA) for detecting cryptococcal GXM antigen in serum and BALF samples from confirmed cases was 97% and 95%, respectively, and the specificity was 98.2% and 93%, respectively, and the differences in these values between the BALF and serum samples were not significant. The serum cryptococcal GXM antigen value showed a positive correlation (r: 0.581, p < 0.001) with pulmonary lesion size, while the BALF value showed no correlation (r: 0.253, p: 0.13). The positivity rate of BALF was higher than that of serum when the diameter of the pulmonary lesion was small (diameter less than 20 mm). Moreover, the serum cryptococcal GXM antigen levels showed an overall decreasing trend with the decrease in pulmonary lesion size after antifungal therapy in patient follow-up.

CONCLUSIONS

The Chinese-made cryptococcal GXM antigen test has better sensitivity and specificity for diagnosing pulmonary cryptococcosis in the HIV-negative Chinese population, and it could be used to diagnose and to monitor this disease.

Novel input polarisation independent endoscopic cross-polarised optical coherence tomography probe

Lead by the original idea to perform noninvasive optical biopsies of various tissues, optical coherence tomography found numerous medical applications within the last two decades. The interference based imaging technique opens the possibility to visualise subcellular morphology up to an imaging depth of 3 mm and up to micron level axial and lateral resolution. The birefringence properties of the tissue are visualised with enhanced contrast using polarisation sensitive or cross-polarised optical coherence tomography (OCT) techniques. Although, it requires strict control over the polarisation states, resulting in several polarisation controlling elements. In this work, we propose a novel input-polarisation independent endoscopic system based on cross-polarised OCT. We tested the feasibility of our approach by measuring the polarisation change from a quarter-wave plate for different rotational angles. Further performance tests reveal a lateral resolution of 30 μm and a sensitivity of 103 dB. Images of the human nail bed and cow muscle tissue demonstrate the potential of the system to measure structural and birefringence properties of the tissue endoscopically.

Recent developments in advanced diagnostic bronchoscopy

The field of bronchoscopy is advancing rapidly. Minimally invasive diagnostic approaches are replacing more aggressive surgical ones for the diagnosis and staging of lung cancer. Evolving diagnostic modalities allow early detection and serve as an adjunct to early treatment, ideally influencing patient outcomes. In this review, we will elaborate on recent bronchoscopic developments as well as some promising investigational tools and approaches in development. We aim to offer a concise overview of the significant advances in the field of advanced bronchoscopy and to put them into clinical context. We will also address potential complications and current diagnostic challenges associated with sampling central and peripheral lung lesions.

Distinguishing Tumor from Associated Fibrosis to Increase Diagnostic Biopsy Yield with Polarization-Sensitive Optical Coherence Tomography

PURPOSE

With recent advancements in personalized medicine, biopsies must contain sufficient tumor for histologic diagnosis and molecular testing. However, inadvertent biopsy of tumor-associated fibrosis compromises tumor yield, resulting in delayed diagnoses and/or repeat procedures when additional tumor is needed. The ability to differentiate tumor from fibrosis intraprocedurally during biopsy could significantly increase tumor yield. Polarization-sensitive optical coherence tomography (PS-OCT) is an imaging modality that is endoscope- and/or needle-compatible, and provides large volumetric views of tissue microstructure with high resolution (∼10 μm) while simultaneously measuring birefringence of organized tissues such as collagen. We aim to determine whether PS-OCT can accurately detect and distinguish tumor-associated fibrosis from tumor.

EXPERIMENTAL DESIGN

PS-OCT was obtained ex vivo in 64 lung nodule samples. PS-OCT birefringence was measured and correlated to collagen content in precisely matched histology, quantified on picrosirius red (PSR) staining.

RESULTS

There was a strong positive correlation between PS-OCT measurement of birefringent fibrosis and total collagen content by PSR (r = 0.793; P < 0.001). In addition, PS-OCT was able to accurately classify tumor regions with >20% fibrosis from those with low fibrosis (≤20%) that would likely yield higher tumor content (P < 0.0001).

CONCLUSIONS

PS-OCT enables accurate fibrosis detection and can distinguish tumor regions with low fibrosis. PS-OCT has significant potential for clinical impact, as the ability to differentiate tumor from fibrosis could be used to guide intraprocedural tissue sampling in vivo, or for rapid biopsy adequacy assessment ex vivo, to increase diagnostic tumor yield essential for patient care and research.

In vivo multifunctional optical coherence tomography at the periphery of the lungs

Remodeling of tissue, such as airway smooth muscle (ASM) and extracellular matrix, is considered a key feature of airways disease. No clinically accepted diagnostic method is currently available to assess airway remodeling or the effect of treatment modalities such as bronchial thermoplasty in asthma, other than invasive airway biopsies. Optical coherence tomography (OCT) generates cross-sectional, near-histological images of airway segments and enables identification and quantification of airway wall layers based on light scattering properties only. In this study, we used a custom motorized OCT probe that combines standard and polarization sensitive OCT (PS-OCT) to visualize birefringent tissue in vivo in the airway wall of a patient with severe asthma in a minimally invasive manner. We used optic axis uniformity (OAxU) to highlight the presence of uniformly arranged fiber-like tissue, helping visualizing the abundance of ASM and connective tissue structures. Attenuation coefficient images of the airways are presented for the first time, showing superior architectural contrast compared to standard OCT images. A novel segmentation algorithm was developed to detect the surface of the endoscope sheath and the surface of the tissue. PS-OCT is an innovative imaging technique that holds promise to assess airway remodeling including ASM and connective tissue in a minimally invasive, real-time manner.

In Vivo and Ex Vivo Microscopy: Moving Toward the Integration of Optical Imaging Technologies Into Pathology Practice

The traditional surgical pathology assessment requires tissue to be removed from the patient, then processed, sectioned, stained, and interpreted by a pathologist using a light microscope. Today, an array of alternate optical imaging technologies allow tissue to be viewed at high resolution, in real time, without the need for processing, fixation, freezing, or staining. Optical imaging can be done in living patients without tissue removal, termed in vivo microscopy, or also in freshly excised tissue, termed ex vivo microscopy. Both in vivo and ex vivo microscopy have tremendous potential for clinical impact in a wide variety of applications. However, in order for these technologies to enter mainstream clinical care, an expert will be required to assess and interpret the imaging data. The optical images generated from these imaging techniques are often similar to the light microscopic images that pathologists already have expertise in interpreting. Other clinical specialists do not have this same expertise in microscopy, therefore, pathologists are a logical choice to step into the developing role of microscopic imaging expert. Here, we review the emerging technologies of in vivo and ex vivo microscopy in terms of the technical aspects and potential clinical applications. We also discuss why pathologists are essential to the successful clinical adoption of such technologies and the educational resources available to help them step into this emerging role.

Needle-based Optical Coherence Tomography to Guide Transbronchial Lymph Node Biopsy

BACKGROUND

Transbronchial needle aspiration (TBNA), often used to sample lymph nodes for lung cancer staging, is subject to sampling error even when performed with endobronchial ultrasound. Optical coherence tomography (OCT) is a high-resolution imaging modality that rapidly generates helical cross-sectional images. We aim to determine if needle-based OCT can provide microstructural information in lymph nodes that may be used to guide TBNA, and improve sampling error.

METHODS

We performed ex vivo needle-based OCT on thoracic lymph nodes from patients with and without known lung cancer. OCT imaging features were compared against matched histology.

RESULTS

OCT imaging was performed in 26 thoracic lymph nodes, including 6 lymph nodes containing metastatic carcinoma. OCT visualized lymphoid follicles, adipose tissue, pigment-laden histiocytes, and blood vessels. OCT features of metastatic carcinoma were distinct from benign lymph nodes, with microarchitectural features that reflected the morphology of the carcinoma subtype. OCT was also able to distinguish lymph node from adjacent airway wall.

CONCLUSIONS

Our results demonstrate that OCT provides critical microstructural information that may be useful to guide TBNA lymph node sampling, as a complement to endobronchial ultrasound. In vivo studies are needed to further evaluate the clinical utility of OCT in thoracic lymph node assessment.

The clinical usefulness of optical coherence tomography during cancer interventions

INTRODUCTION

Tumor detection and visualization plays a key role in the clinical workflow of a patient with suspected cancer, both in the diagnosis and treatment. Several optical imaging techniques have been evaluated for guidance during oncological interventions. Optical coherence tomography (OCT) is a technique which has been widely evaluated during the past decades. This review aims to determine the clinical usefulness of OCT during cancer interventions focussing on qualitative features, quantitative features and the diagnostic value of OCT.

METHODS

A systematic literature search was performed for articles published before May 2018 using OCT in the field of surgical oncology. Based on these articles, an overview of the clinical usefulness of OCT was provided per tumor type.

RESULTS

A total of 785 articles were revealed by our search, of which a total of 136 original articles were available for analysis, which formed the basis of this review. OCT is currently utilised for both preoperative diagnosis and intraoperative detection of skin, oral, lung, breast, hepatobiliary, gastrointestinal, urological, and gynaecological malignancies. It showed promising results in tumor detection on a microscopic level, especially using higher resolution imaging techniques, such as high-definition OCT and full-field OCT.

CONCLUSION

In the near future, OCT could be used as an additional tool during bronchoscopic or endoscopic interventions and could also be implemented in margin assessment during (laparoscopic) cancer surgery if a laparoscopic or handheld OCT device will be further developed to make routine clinical use possible.

Processing-based approach for resolving the sample optic axis in endoscopic polarization-sensitive optical coherence tomography

Fiber-based polarization-sensitive optical coherence tomography (PS-OCT) that utilizes a rotationally-scanning catheter has a variety of potential biomedical applications in luminal organ systems due to its ability to provide intrinsic contrast for birefringent tissue. Incorporating the optic axis (OA) of the tissue greatly enhances this potential by also permitting information about the orientation of the tissue to be extracted; however, measurement distortion that occurs has up to this point made it impossible to obtain accurate sample OA measurements. In this paper we present a straightforward calibration technique that allows the sample OA to be recovered. This technique requires no hardware modifications making it generally applicable, and as a result has tremendous potential in improving the utility of endoscopic PS-OCT image data.

Nano-optic endoscope for high-resolution optical coherence tomography in vivo

Acquisition of high-resolution images from within internal organs using endoscopic optical imaging has numerous clinical applications. However, difficulties associated with optical aberrations and the trade-off between transverse resolution and depth-of-focus significantly limit the scope of applications. Here, we integrate a metalens, with the ability to modify the phase of incident light at sub-wavelength level, into the design of an endoscopic optical coherence tomography catheter (termed nano-optic endoscope) to achieve near diffraction-limited imaging through negating non-chromatic aberrations. Remarkably, the tailored chromatic dispersion of the metalens in the context of spectral interferometry is utilized to maintain high-resolution imaging beyond the input field Rayleigh range, easing the trade-off between transverse resolution and depth-of-focus. We demonstrate endoscopic imaging both in resected human lung specimens and in sheep airways in vivo. The combination of the superior resolution and higher imaging depth-of-focus of the nano-optic endoscope will likely increase the clinical utility of endoscopic optical imaging.

Optimal endobronchial tool sizes for targeting lung lesions based on 3D modeling

Background

For patients with suspicious lung lesions found on chest x-ray or CT, endo/trans- bronchial biopsy of the lung is the preferred method for obtaining a diagnosis. With the addition of new screening programs, a higher number of patients will require diagnostic biopsy which will prove even more challenging due to the small size of lesions found with screening. There are many endobronchial tools available on the market today and a wide range of new tools under investigation to improve diagnostic yield. However, there is little information available about the optimal tool size required to reach the majority of lesions, especially peripheral ones. In this manuscript we investigate the percentage of lesions that can be reached for various diameter tools if the tools remain inside the airways (i.e. endobronchial biopsy) and the distance a tool must travel “off-road” (or outside of the airways) to reach all lesions.

Methods and findings

To further understand the distribution of lung lesions with respect to airway sizes and distances from the airways, six 3D models of the lung were generated. The airways were modeled at two different respiratory phases (inspiration and expiration). Three sets of 1,000 lesions were randomly distributed throughout the lung for each respiratory phase. The simulations showed that the percentage of reachable lesions decreases with increasing tool diameter and decreasing lesion diameter. A 1mm diameter tool will reach <25% of 1cm lesions if it remains inside the airways. To reach all 1cm lesions this 1mm tool would have to navigate through the parenchyma up to 8.5mm. CT scans of 21 patient lesions confirm these results reasonably well.

Conclusions

The smaller the tool diameter the more likely it will be able to reach a lung lesion, whether it be for diagnostic biopsy, ablation, or resection. However, even a 1mm tool is not small enough to reach the majority of small (1-2cm) lesions. Therefore, it is necessary for endobronchial tools to be able to navigate through the parenchyma to reach the majority of lesions.

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.

Flexible needle with integrated optical coherence tomography probe for imaging during transbronchial tissue aspiration

Transbronchial needle aspiration (TBNA) of small lesions or lymph nodes in the lung may result in nondiagnostic tissue samples. We demonstrate the integration of an optical coherence tomography (OCT) probe into a 19-gauge flexible needle for lung tissue aspiration. This probe allows simultaneous visualization and aspiration of the tissue. By eliminating the need for insertion and withdrawal of a separate imaging probe, this integrated design minimizes the risk of dislodging the needle from the lesion prior to aspiration and may facilitate more accurate placement of the needle. Results from in situ imaging in a sheep lung show clear distinction between solid tissue and two typical constituents of nondiagnostic samples (adipose and lung parenchyma). Clinical translation of this OCT-guided aspiration needle holds promise for improving the diagnostic yield of TBNA.

Polarization sensitive optical coherence tomography - a review [Invited]

Optical coherence tomography (OCT) is now a well-established modality for high-resolution cross-sectional and three-dimensional imaging of transparent and translucent samples and tissues. Conventional, intensity based OCT, however, does not provide a tissue-specific contrast, causing an ambiguity with image interpretation in several cases. Polarization sensitive (PS) OCT draws advantage from the fact that several materials and tissues can change the light's polarization state, adding an additional contrast channel and providing quantitative information. In this paper, we review basic and advanced methods of PS-OCT and demonstrate its use in selected biomedical applications.

Early lung cancer detection, mucosal, and alveolar imaging

PURPOSE OF REVIEW

Lung cancer is the leading cause of cancer deaths worldwide. Early detection is essential for long-term survival. Screening of high-risk individuals with low-dose computed tomography screening has proven to increase survival. However, current radiological imaging techniques have poor specificity for lung cancer detection and poor sensitivity for detection of mucosal or alveolar preinvasive malignant lesions. Bronchoscopy allows imaging and sampling of early lung cancer, with the highest safety profile and high diagnostic accuracy.

RECENT FINDINGS

Available technologies, such as autofluorescence bronchoscopy, narrow band imaging, and radial ultrasound bronchoscopy can significantly increase the yield and diagnostic accuracy of bronchoscopy for early cancer detection in the central airways. Newer technologies such as optical coherence tomography, confocal bronchoscopy, and Raman spectroscopy may significantly increase the diagnostic yield of both central and parenchymal early cancer lesions.

SUMMARY

Although some of these technologies are still investigational and are not readily available in most centers, they may identify early mucosal and alveolar cancer lesions accurately in the least invasive manner to provide appropriate therapy and prolong patient survival from lung cancer.

Deep tissue volume imaging of birefringence through fibre-optic needle probes for the delineation of breast tumour

Identifying tumour margins during breast-conserving surgeries is a persistent challenge. We have previously developed miniature needle probes that could enable intraoperative volume imaging with optical coherence tomography. In many situations, however, scattering contrast alone is insufficient to clearly identify and delineate malignant regions. Additional polarization-sensitive measurements provide the means to assess birefringence, which is elevated in oriented collagen fibres and may offer an intrinsic biomarker to differentiate tumour from benign tissue. Here, we performed polarization-sensitive optical coherence tomography through miniature imaging needles and developed an algorithm to efficiently reconstruct images of the depth-resolved tissue birefringence free of artefacts. First ex vivo imaging of breast tumour samples revealed excellent contrast between lowly birefringent malignant regions, and stromal tissue, which is rich in oriented collagen and exhibits higher birefringence, as confirmed with co-located histology. The ability to clearly differentiate between tumour and uninvolved stroma based on intrinsic contrast could prove decisive for the intraoperative assessment of tumour margins.

Diagnosing lung carcinomas with optical coherence tomography

RATIONALE

Lung carcinoma diagnosis on tissue biopsy can be challenging because of insufficient tumor and lack of architectural information. Optical coherence tomography (OCT) is a high-resolution imaging modality that visualizes tissue microarchitecture in volumes orders of magnitude larger than biopsy. It has been proposed that OCT could potentially replace tissue biopsy.

OBJECTIVES

We aim to determine whether OCT could replace histology in diagnosing lung carcinomas. We develop and validate OCT interpretation criteria for common primary lung carcinomas: adenocarcinoma, squamous cell carcinoma (SCC), and poorly differentiated carcinoma.

METHODS

A total of 82 ex vivo tumor samples were included in a blinded assessment with 3 independent readers. Readers were trained on the OCT criteria, and applied these criteria to diagnose adenocarcinoma, SCC, or poorly differentiated carcinoma in an OCT validation dataset. After a 7-month period, the readers repeated the training and validation dataset interpretation. An independent pathologist reviewed corresponding histology.

MEASUREMENTS AND MAIN RESULTS

The average accuracy achieved by the readers was 82.6% (range, 73.7-94.7%). The sensitivity and specificity for adenocarcinoma were 80.3% (65.7-91.4%) and 88.6% (80.5-97.6%), respectively. The sensitivity and specificity for SCC were 83.3% (70.0-100.0%) and 87.0% (75.0-96.5%), respectively. The sensitivity and specificity for poorly differentiated carcinoma were 85.7% (81.0-95.2%) and 97.6% (92.9-100.0%), respectively.

CONCLUSIONS

Although these results are encouraging, they indicate that OCT cannot replace histology in the diagnosis of lung carcinomas. However, OCT has potential to aid in diagnosing lung carcinomas as a complement to tissue biopsy, particularly when insufficient tissue is available for pathology assessment.

Endoscopic Doppler optical coherence tomography and autofluorescence imaging of peripheral pulmonary nodules and vasculature

We present the first endoscopic Doppler optical coherence tomography and co-registered autofluorescence imaging (DOCT-AFI) of peripheral pulmonary nodules and vascular networks in vivo using a small 0.9 mm diameter catheter. Using exemplary images from volumetric data sets collected from 31 patients during flexible bronchoscopy, we demonstrate how DOCT and AFI offer complementary information that may increase the ability to locate and characterize pulmonary nodules. AFI offers a sensitive visual presentation for the rapid identification of suspicious airway sites, while co-registered OCT provides detailed structural information to assess the airway morphology. We demonstrate the ability of AFI to visualize vascular networks in vivo and validate this finding using Doppler and structural OCT. Given the advantages of higher resolution, smaller probe size, and ability to visualize vasculature, DOCT-AFI has the potential to increase diagnostic accuracy and minimize bleeding to guide biopsy of pulmonary nodules compared to radial endobronchial ultrasound, the current standard of care.

Optical coherence tomography in respiratory science and medicine: from airways to alveoli

Optical coherence tomography is a rapidly maturing optical imaging technology, enabling study of the in vivo structure of lung tissue at a scale of tens of micrometers. It has been used to assess the layered structure of airway walls, quantify both airway lumen caliber and compliance, and image individual alveoli. This article provides an overview of the technology and reviews its capability to provide new insights into respiratory disease.

Polarization sensitive optical frequency domain imaging system for endobronchial imaging

A polarization sensitive endoscopic optical frequency domain imaging (PS-OFDI) system with a motorized distal scanning catheter is demonstrated. It employs a passive polarization delay unit to multiplex two orthogonal probing polarization states in depth, and a polarization diverse detection unit to detect interference signal in two orthogonal polarization channels. Per depth location four electro-magnetic field components are measured that can be represented in a complex 2x2 field matrix. A Jones matrix of the sample is derived and the sample birefringence is extracted by eigenvalue decomposition. The condition of balanced detection and the polarization mode dispersion are quantified. A complex field averaging method based on the alignment of randomly pointing field phasors is developed to reduce speckle noise. The variation of the polarization states incident on the tissue due to the circular scanning and catheter sheath birefringence is investigated. With this system we demonstrated imaging of ex vivo chicken muscle, in vivo pig lung and ex vivo human lung specimens.

Advances in interventional pulmonology

Interventional pulmonology (IP) remains a rapidly expanding and evolving subspecialty focused on the diagnosis and treatment of complex diseases of the thorax. As the field continues to push the leading edge of medical technology, new procedures allow for novel minimally invasive approaches to old diseases including asthma, chronic obstructive pulmonary disease and metastatic or primary lung malignancy. In addition to technologic advances, IP has matured into a defined subspecialty, requiring formal training necessary to perform the advanced procedures. This need for advanced training has led to the need for standardization of training and the institution of a subspecialty board examination. In this review, we will discuss the dynamic field of IP as well as novel technologies being investigated or employed in the treatment of thoracic disease.