Swept source optical coherence microscopy for pathological assessment of cancerous tissues

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.Includes bibliographical references.Optical coherence microscopy (OCM) combines optical coherence tomography (OCT) with confocal microscopy and enables depth resolved visualization of biological specimens with cellular resolution. OCM offers a suitable alternative to confocal imaging by providing enhanced contrast due to the additional coherence gate to the inherent confocal gate, increasing the field of view and imaging depth, and eliminating the need of external contrast agents. In the past, development of OCT systems have been focused on time domain and spectral/Fourier domain methods which offer high axial resolution and imaging speeds. However, recent advances in the OCT technology have pushed the development into the direction of swept source OCT technologies, and development of the OCM technology is likely to follow this path. This thesis describes construction, characterization and preliminary imaging results of a swept source OCM (SS-OCM) system utilizing a novel light source, Vertical Cavity Surface-Emission Laser (VCSEL). This swept source laser can reach sweep rates exceeding 1 MHz and provide wide tuning ranges, which will enable both imaging speeds approaching to time domain OCM (TD-OCM) systems, and axial resolution approaching to spectral/Fourier domain OCM (SD-OCM) systems. Several other advantages of SS-OCM compared to TD-OCM and SD-OCM that make this technology a promising alternative to the latter imaging methods are presented. Furthermore, practical concepts in the system development and signal processing, such as compensation for the scan curvatures, methods for calibration of the spectrums, selection of suitable color maps for display, and other related topics are also discussed in the text. In addition to technical description of the OCM system development, an in depth analysis of several clinical applications that will be likely to benefit from this imaging modality is also presented. Real time intraoperative feedback is required in order to reduce the morbidity and the rate of additional operations for the surgical management of several forms of cancer, where a benchtop OCM system residing in the pathology laboratory can be immensely beneficial. Furthermore, with the novel scanning mechanisms that have been developed in the recent years it is possible to translate this imaging modality to an in vivo setting where an OCM probe can be inserted through the working channel of an endoscope and generate cellular resolution images in real time without the need of external contrast agents. Endoscopic management and clinical challenges for a spectrum of lower gastrointestinal (GI) diseases is discussed where an in vivo OCM imaging probe can play an important role in the diagnosis and evaluation of the extend of the particular disease. A review of alternative imaging modalities, such as chromoendoscopy, narrow band imaging (NBI) and confocal laser endomicroscopy (CLE) is also included which outlines the relative strengths and limitations of these imaging modalities for the clinical management of lower GI diseases.by Osman Oguz Ahsen.S.M

Optical Imaging Techniques for the Detection of Esophageal Neoplasia in Barrett’s Esophagus

The main objective of this research was to develop a two-stage optical imaging platform to improve detection of cancer in Barrett’s esophagus (BE). BE caused by chronic reflux and patients with BE are at a higher risk for developing esophageal adenocarcinoma (EAC). However, neoplasia in BE is often unidentifiable under standard endoscopy, and studies have shown nearly half of early cancers can go unidentified by this method. Widefield imaging (resolves ~100 microns) allows efficient surveillance of large BE segments. Two widefield imaging techniques were identified to improve contrast between benign and abnormal lesions during an ex vivo 15 patient feasibility study. Cross-polarized imaging (CPI) reduced specular reflection and improved vascular contrast. Vital-dye fluorescence imaging (VFI) using topically-applied proflavine improved visualization of glandular pattern. Moreover, relevant pathologic features visible during VFI were seen in corresponding histology slides as well as high resolution images of the same sites. Based on these results, a cap-based Multispectral Digital Endoscope (MDE) was designed and built. The MDE can image in three different imaging modes: white light imaging, CPI, and VFI. Modifications to a Pentax EPK-i video processor and a Pentax endoscope were made to incorporate these imaging modes into one system. A 21 patient in vivo pilot study with 65 pathologically correlated sites demonstrated the feasibility of using this system in vivo; image criteria were developed to classify neoplasia with a sensitivity and specificity of 100% and 76% respectively. High resolution imaging (resolves ~2-5 micron) may verify the disease presence in suspicious areas identified using widefield techniques. 2-NBDG, a fluorescent metabolic marker, was used as to identify neoplastic biopsies. In a study with 21 patients yielding 38 pathologically correlated biopsies and 158 image sites, 2-NBDG imaging allowed classification of cancerous biopsies with a sensitivity of 96% and specificity of 90%. The unique contributions of these results is the development of a multimodal cap-based endoscopic system to identify suspicious areas in BE, and using a metabolic marker to verify the presence of disease. This application extends beyond esophageal cancer detection and may be explored for cancer detection in other organ sites characterized by columnar epithelium

State of the art in advanced endoscopic imaging for the detection and evaluation of dysplasia and early cancer of the gastrointestinal tract

Ideally, endoscopists should be able to detect, characterize, and confirm the nature of a lesion at the bedside, minimizing uncertainties and targeting biopsies and resections only where necessary. However, under conventional white-light inspection – at present, the sole established technique available to most of humanity – premalignant conditions and early cancers can frequently escape detection. In recent years, a range of innovative techniques have entered the endoscopic arena due to their ability to enhance the contrast of diseased tissue regions beyond what is inherently possible with standard white-light endoscopy equipment. The aim of this review is to provide an overview of the state-of-the-art advanced endoscopic imaging techniques available for clinical use that are impacting the way precancerous and neoplastic lesions of the gastrointestinal tract are currently detected and characterized at endoscopy. The basic instrumentation and the physics behind each method, followed by the most influential clinical experience, are described. High-definition endoscopy, with or without optical magnification, has contributed to higher detection rates compared with white-light endoscopy alone and has now replaced ordinary equipment in daily practice. Contrast-enhancement techniques, whether dye-based or computed, have been combined with white-light endoscopy to further improve its accuracy, but histology is still required to clarify the diagnosis. Optical microscopy techniques such as confocal laser endomicroscopy and endocytoscopy enable in vivo histology during endoscopy; however, although of invaluable assistance for tissue characterization, they have not yet made transition between research and clinical use. It is still unknown which approach or combination of techniques offers the best potential. The optimal method will entail the ability to survey wide areas of tissue in concert with the ability to obtain the degree of detailed information provided by microscopic techniques. In this respect, the challenging combination of autofluorescence imaging and confocal endomicroscopy seems promising, and further research is awaited

An Investigation of the Diagnostic Potential of Autofluorescence Lifetime Spectroscopy and Imaging for Label-Free Contrast of Disease

The work presented in this thesis aimed to study the application of fluorescence lifetime spectroscopy (FLS) and fluorescence lifetime imaging microscopy (FLIM) to investigate their potential for diagnostic contrast of diseased tissue with a particular emphasis on autofluorescence (AF) measurements of gastrointestinal (GI) disease. Initially, an ex vivo study utilising confocal FLIM was undertaken with 420 nm excitation to characterise the fluorescence lifetime (FL) images obtained from 71 GI samples from 35 patients. A significant decrease in FL was observed between normal colon and polyps (p = 0.024), and normal colon and inflammatory bowel disease (IBD) (p = 0.015). Confocal FLIM was also performed on 23 bladder samples. A longer, although not significant, FL for cancer was observed, in paired specimens (n = 5) instilled with a photosensitizer. The first in vivo study was a clinical investigation of skin cancer using a fibre-optic FL spectrofluorometer and involved the interrogation of 27 lesions from 25 patients. A significant decrease in the FL of basal cell carcinomas compared to healthy tissue was observed (p = 0.002) with 445 nm excitation. A novel clinically viable FLS fibre-optic probe was then applied ex vivo to measure 60 samples collected from 23 patients. In a paired analysis of neoplastic polyps and normal colon obtained from the same region of the colon in the same patient (n = 12), a significant decrease in FL was observed (p = 0.021) with 435 nm excitation. In contrast, with 375 nm excitation, the mean FL of IBD specimens (n = 4) was found to be longer than that of normal tissue, although not statistically significant. Finally, the FLS system was applied in vivo in 17 patients, with initial data indicating that 435 nm excitation results in AF lifetimes that are broadly consistent with ex vivo studies, although no diagnostically significant differences were observed in the signals obtained in vivo.Open Acces

Endoscopic multimodal imaging in Barrett's oesophagus

The incidence of oesophageal adenocarcinoma (OA) has increased exponentially in the western world over the past few decades. Barrett's oesophagus (BO) is a well known precursor of OA with a risk approximately 20 times more than that of background population. Regular endoscopic surveillance in patients with BO is recommended by most of the national gastroenterological societies. The advantage of Barrett's surveillance is to identify early subtle lesions which could then be managed early to avoid symptomatic and advanced cancers. The detection of such early lesions are challenging as they could be flat and inconspicuous on routine endoscopic examination. In the absence of any lesions, four quadrant biopsies every 1-2 cm of the whole length of Barrett's oesophagus is advised. This technique would map only 5-10% of the surface area of Barrett's segment and hence it is associated with significant sampling error. The improvement in electronics over the past decade has led to the production of endoscopes with better charged coupled devices and image enhancement techniques by altering the spectrum of light. This thesis examines the role of multi modal imaging in Barrett's oesophagus with a focus on detecting dysplasia and early cancer (EC). Firstly, the role of high definition (HD) imaging in routine clinical setting was studied using data from patients who have undergone Barrett's· surveillance. The yield of dysplasia by HD endoscopy was compared to standard definition (SD) endoscopy in this study. The role of narrow band imaging (NBI) with magnification in characterising abnormal lesions detected during BO surveillance was evaluated by performing a meta- analysis of clinical studies. The role of autofluorescence imaging (AFI) in Barrett's oesophagus was examined in detail with a view to understand the biological basis of autofluorescence and to improve the specificity of this technique as it is associated with significant false positive results in clinical studies. A meta-analysis was performed to identify whether AFI has a clinical advantage over white light endoscopy in detecting Barrett's dysplasia and the inter-observer reliability of this technology was studied using AFI expert and AFI non-expert endoscopists. An objective method of measuring the autofluorescence intensity was proposed as a ratio of the red to the green colour tone (AF ratio) of the area of interest. When the AF ratio of the lesion was divided by the AF ratio of the background mucosa, an AF index is obtained. A pilot study was performed to identify a cut-off value of AF index to differentiate high grade dysplasia (HGD) and EC from non-dysplastic BO. Finally, the biological basis of AF intensity was examined using APCmin mouse colonic models. This study looked into the AF ratio of the colonic mucosal lesions and correlated it with the amount of collagen and elastin in the submucosal tissue. Collagen and elastin are known to be the strongest fluorophores of the gastrointestinal tract and the question addressed is whether the low AF intensity associated with dysplastic lesions is due to the thickening of mucosa or to a reduction of collagen and elastin

Endoscopic multimodal imaging in Barrett's oesophagus

The incidence of oesophageal adenocarcinoma (OA) has increased exponentially in the western world over the past few decades. Barrett's oesophagus (BO) is a well known precursor of OA with a risk approximately 20 times more than that of background population. Regular endoscopic surveillance in patients with BO is recommended by most of the national gastroenterological societies. The advantage of Barrett's surveillance is to identify early subtle lesions which could then be managed early to avoid symptomatic and advanced cancers. The detection of such early lesions are challenging as they could be flat and inconspicuous on routine endoscopic examination. In the absence of any lesions, four quadrant biopsies every 1-2 cm of the whole length of Barrett's oesophagus is advised. This technique would map only 5-10% of the surface area of Barrett's segment and hence it is associated with significant sampling error. The improvement in electronics over the past decade has led to the production of endoscopes with better charged coupled devices and image enhancement techniques by altering the spectrum of light. This thesis examines the role of multi modal imaging in Barrett's oesophagus with a focus on detecting dysplasia and early cancer (EC). Firstly, the role of high definition (HD) imaging in routine clinical setting was studied using data from patients who have undergone Barrett's· surveillance. The yield of dysplasia by HD endoscopy was compared to standard definition (SD) endoscopy in this study. The role of narrow band imaging (NBI) with magnification in characterising abnormal lesions detected during BO surveillance was evaluated by performing a meta- analysis of clinical studies. The role of autofluorescence imaging (AFI) in Barrett's oesophagus was examined in detail with a view to understand the biological basis of autofluorescence and to improve the specificity of this technique as it is associated with significant false positive results in clinical studies. A meta-analysis was performed to identify whether AFI has a clinical advantage over white light endoscopy in detecting Barrett's dysplasia and the inter-observer reliability of this technology was studied using AFI expert and AFI non-expert endoscopists. An objective method of measuring the autofluorescence intensity was proposed as a ratio of the red to the green colour tone (AF ratio) of the area of interest. When the AF ratio of the lesion was divided by the AF ratio of the background mucosa, an AF index is obtained. A pilot study was performed to identify a cut-off value of AF index to differentiate high grade dysplasia (HGD) and EC from non-dysplastic BO. Finally, the biological basis of AF intensity was examined using APCmin mouse colonic models. This study looked into the AF ratio of the colonic mucosal lesions and correlated it with the amount of collagen and elastin in the submucosal tissue. Collagen and elastin are known to be the strongest fluorophores of the gastrointestinal tract and the question addressed is whether the low AF intensity associated with dysplastic lesions is due to the thickening of mucosa or to a reduction of collagen and elastin

New Techniques in Gastrointestinal Endoscopy

As result of progress, endoscopy has became more complex, using more sophisticated devices and has claimed a special form. In this moment, the gastroenterologist performing endoscopy has to be an expert in macroscopic view of the lesions in the gut, with good skills for using standard endoscopes, with good experience in ultrasound (for performing endoscopic ultrasound), with pathology experience for confocal examination. It is compulsory to get experience and to have patience and attention for the follow-up of thousands of images transmitted during capsule endoscopy or to have knowledge in physics necessary for autofluorescence imaging endoscopy. Therefore, the idea of an endoscopist has changed. Examinations mentioned need a special formation, a superior level of instruction, accessible to those who have already gained enough experience in basic diagnostic endoscopy. This is the reason for what these new issues of endoscopy are presented in this book of New techniques in Gastrointestinal Endoscopy

Genetic, clinical and pathological factors in management and surveillance of patients with colorectal tumours

Numerous factors influence an individual’s risk of colorectal cancer, including pathological features such as polyp size and multiplicity, and family history of colorectal malignancy. In clinical practice polyp size can be measured at different time points, however adenoma surveillance guidelines do not define which measurement to utilise, due to variance in data source. The initial study compared the measurements of 107 polyps. Variation in surveillance intervals occurred less frequently with postfixation than in situ measurements (5.6 versus 9.5%), supporting the use of post-fixation polyp size. A further study considered the level of agreement amongst histopathologists in Wales in the reporting of colorectal polyps. Only fair agreement (k = 0.24) was observed in the reporting of the completeness of excision. A lesion with epithelial misplacement and high grade dysplasia was misclassified as adenocarcinoma by five pathologists, indicating the need for further training and potential introduction of a formal accreditation process. Individuals with a moderate family history risk of colorectal cancer are at increased risk of colorectal lesions. Pathways through the Welsh genetics service were studied. 63.4% referrals were received from primary care. The majority of patient’s were female (70.8%). 93.8% patients were advised to undergo 5-yearly surveillance. Existing referral pathways were found to be complex increasing the risk of over/under surveillance. Little is known about colonoscopic surveillance outcomes following genetic assessment. A study of 172 patients revealed an adenoma detection rate (ADR) of 11.1% and advanced ADR of 4.1% at the index procedure. Cancer was diagnosed in 0.6% cases. The majority of lesions identified were diminutive low grade adenomas. Several endoscopic modalities have been utilised to enhance polyp detection in patients with a propensity to colonic polyps. Narrow band imaging was studied in 37 high-moderate risk patients, but did not significantly increase polyp yield above high definition white light colonoscopy