Characterization of dysplastic tissue morphology and biochemistry in Barrett's esophagus using diffuse reflectance and light scattering spectroscopy

Endoscopic imaging of Barrett’s esophagus

The incidence of esophageal adenocarcinoma (EAC) has dramatically increased in the United States as well as Western European countries. The majority of esophageal adenocarcinomas arise from a backdrop of Barrett’s esophagus (BE), a premalignant lesion that can lead to dysplasia and cancer. Because of the increased risk of EAC, GI society guidelines recommend endoscopic surveillance of patients with BE. The emphasis on early detection of dysplasia in BE through surveillance endoscopy has led to the development of advanced endoscopic imaging technologies. These techniques have the potential to both improve mucosal visualization and characterization and to detect small mucosal abnormalities which are difficult to identify with standard endoscopy. This review summarizes the advanced imaging technologies used in evaluation of BE.

Characterizing the beam steering and distortion of Gaussian and Bessel beams focused in tissues with microscopic heterogeneities

Bessel beams have recently been investigated as a means of improving deep-tissue microscopy in highly scattering and heterogeneous media. It has been suggested that the long depth-of-field and self-reconstructing property of a Bessel beam enables an increased penetration depth of the focused beam in tissues compared to a conventional Gaussian beam. However, a study is needed to better quantify the magnitude of the beam steering as well as the distortion of focused Gaussian and Bessel beams in tissues with microscopic heterogeneities. Here, we have developed an imaging method and quantitative metrics to evaluate the motion and distortion of low-numerical-aperture (NA) Gaussian and Bessel beams focused in water, heterogeneous phantoms, and fresh mouse esophagus tissues. Our results indicate that low-NA Bessel beams exhibit reduced beam-steering artifacts and distortions compared to Gaussian beams, and are therefore potentially useful for microscopy applications in which pointing accuracy and beam quality are critical, such as dual-axis confocal (DAC) microscopy.

The use of imaging and biomarkers in diagnosing Barrett's esophagus and predicting the risk of neoplastic progression

Long-standing gastroesophageal reflux disease can result in transformation of the normal squamous lining of the esophagus into columnar epithelium (with goblet cells). This condition, Barrett's esophagus (BE), is considered a risk factor for esophageal cancer (EAC) and may be the cause of the increased incidence of EAC over the last few decades. Currently, endoscopy with biopsies revealing dysplasia is the best predictor for neoplastic progression in patients with BE. However, the use of more sophisticated imaging techniques and biomarkers with or without histological assessment may be helpful in more accurate prediction of malignant transformation in these patients. New approaches to the evaluation of BE such as epigenetics, miRNA analysis, detection of DNA content abnormalities and loss of heterozygosity have great potential to shed light on the complex gastroesophageal reflux disease -BE-EAC sequence.

In vivo optical tissue differentiation by diffuse reflectance spectroscopy: preliminary results for tissue-specific laser surgery

OBJECTIVES

Laser surgery requires feedback to avoid the accidental destruction of critically important tissues. It was the aim of the authors to identify different tissue types in vivo by diffuse reflectance spectroscopy to set the basis for tissue-specific control of laser surgery.

METHODS

Tissue differentiation was performed on in vivo tissue of rats (skin, fat, muscle, and nerve) by diffuse reflectance spectroscopy between 350 and 650 nm. Data analysis was done using principal components analysis, followed by linear discriminant analysis (LDA). The differentiation performance was evaluated by receiver operating characteristic (ROC) analysis.

RESULTS

ROC analysis showed a tissue differentiation of 100%, with a high sensitivity of more than 99%. Only the tissue pair skin/fat showed a reduced differentiation performance and specificity.

CONCLUSION

The results show the general viability of in vivo optical tissue differentiation and create a basis for the further development of a control system for tissue-specific laser surgery.

Measurement of the reduced scattering coefficient of turbid media using single fiber reflectance spectroscopy: fiber diameter and phase function dependence

This paper presents a relationship between the intensity collected by a single fiber reflectance device (R(SF)) and the fiber diameter (d(fib)) and the reduced scattering coefficient ( μs') and phase function (p(θ)) of a turbid medium. Monte Carlo simulations are used to identify and model a relationship between R(SF) and dimensionless scattering ( μs'dfib). For μs'dfib > 10 we find that R(SF) is insensitive to p(θ). A solid optical phantom is constructed with μs' ≈ 220 mm-1 and is used to convert R(SF) of any turbid medium to an absolute scale. This calibrated technique provides accurate estimates of μs' over a wide range ([0.05 - 8] mm(-1)) for a range of d(fib) ([0.2 - 1] mm).

Optical molecular imaging for detection of Barrett’s-associated neoplasia

Recent advancements in the endoscopic imaging of Barrett’s esophagus can be used to probe a wide range of optical properties that are altered with neoplastic progression. This review summarizes relevant changes in optical properties as well as imaging approaches that measures those changes. Wide-field imaging approaches include narrow-band imaging that measures changes in light scattering and absorption, and autofluorescence imaging that measure changes in endogenous fluorophores. High-resolution imaging approaches include optical coherence tomography, endocytoscopy, confocal microendoscopy, and high-resolution microendoscopy. These technologies, some coupled with an appropriate contrast agent, can measure differences in glandular morphology, nuclear morphology, or vascular alterations associated with neoplasia. Advances in targeted contrast agents are further discussed. Studies that have explored these technologies are highlighted; as are the advantages and limitations of each.

Endoscopic evaluation and advanced imaging of Barrett's esophagus

Enhanced visualization techniques are available for Barrett's esophagus and have promise in the detection of dysplasia and cancer. Several of these techniques, such as narrow band imaging and chromoendoscopy, are being applied clinically. These techniques will allow the endoscopist to screen the surface of the Barrett's esophagus to detect areas of neoplasia. Once detected, it is hoped that either magnification techniques, such as confocal laser endomicroscopy, or spectroscopic techniques can be of value in allowing in vivo real-time diagnostic capabilities.

Diffuse reflectance spectroscopy for optical soft tissue differentiation as remote feedback control for tissue-specific laser surgery

BACKGROUND AND OBJECTIVE

Laser surgery does not provide haptic feedback for operating layer-by-layer and thereby preserving vulnerable anatomical structures like nerve tissue or blood vessels. Diffuse reflectance spectra can facilitate remote optical tissue differentiation. It is the aim of the study to use this technique on soft tissue samples, to set a technological basis for a remote optical feedback system for tissue-specific laser surgery.

MATERIALS AND METHODS

Diffuse reflectance spectra (wavelength range: 350-650 nm) of ex vivo types of soft tissue (a total of 10,800 spectra) of the midfacial region of domestic pigs were remotely measured under reduced environmental light conditions and analyzed in order to differentiate between skin, mucosa, muscle, subcutaneous fat, and nerve tissue. We performed a principal components (PC) analysis (PCA) to reduce the number of variables. Linear discriminant analysis (LDA) was utilized for classification. For the tissue differentiation, we calculated the specificity and sensitivity by receiver operating characteristic (ROC) analysis and the area under curve (AUC).

RESULTS

Six PCs were found to be adequate for tissue differentiation with diffuse reflectance spectra using LDA. All of the types of soft tissue could be differentiated with high specificity and sensitivity. Only the tissue pairs nervous tissue/fatty tissue and nervous tissue/mucosa showed a decline of differentiation due to bio-structural similarity. However, both of these tissue pairs could still be differentiated with a specificity and sensitivity of more than 90%.

CONCLUSIONS

Analyzing diffuse reflectance spectroscopy with PCA and LDA allows for remote differentiation of biological tissue. Considering the limitations of the ex vivo conditions, the obtained results are promising and set a basis for the further development of a feedback system for tissue-specific laser surgery.

New technologies for human cancer imaging

Despite technical advances in many areas of diagnostic radiology, the detection and imaging of human cancer remains poor. A meaningful impact on cancer screening, staging, and treatment is unlikely to occur until the tumor-to-background ratio improves by three to four orders of magnitude (ie, 10(3)- to 10(4)-fold), which in turn will require proportional improvements in sensitivity and contrast agent targeting. This review analyzes the physics and chemistry of cancer imaging and highlights the fundamental principles underlying the detection of malignant cells within a background of normal cells. The use of various contrast agents and radiotracers for cancer imaging is reviewed, as are the current limitations of ultrasound, x-ray imaging, magnetic resonance imaging (MRI), single-photon emission computed tomography, positron emission tomography (PET), and optical imaging. Innovative technologies are emerging that hold great promise for patients, such as positron emission mammography of the breast and spectroscopy-enhanced colonoscopy for cancer screening, hyperpolarization MRI and time-of-flight PET for staging, and ion beam-induced PET scanning and near-infrared fluorescence-guided surgery for cancer treatment. This review explores these emerging technologies and considers their potential impact on clinical care. Finally, those cancers that are currently difficult to image and quantify, such as ovarian cancer and acute leukemia, are discussed.

Advanced imaging and technology in gastrointestinal neoplasia: summary of the AGA-NCI Symposium October 4-5, 2004

Imaging and other advanced technologies for detection of gastrointestinal cancers are undergoing a major revolution on several fronts. This is facilitated by convergence of key technologies including advanced endoscopic-detection systems, more specific contrast agents, rapid and high-resolution cross-sectional imaging, and miniaturization of construction systems for making all imaging equipment smaller and less invasive. This convergence is occurring along traditional translational research pathways (clinical medicine-molecular biology) as well as nontraditional lines (clinical medicine-optical physics/engineering and molecular biology-optical physics/engineering). These new efforts are producing a wide array of technologies aimed at improving detection, classification, and monitoring of gastrointestinal neoplasia, especially for colorectal and esophageal cancer because of easier accessibility. A critical goal is to detect lesions at their premalignant stages, thereby permitting meaningful intervention. Inspired by these advances, the American Gastroenterological Association and the National Cancer Institute sponsored a symposium held in Bethesda, MD, from October 4-5, 2004, bringing together leading investigators with diverse backgrounds in imaging technology. The aims of this symposium were to summarize the state of the art and priorities for research in the coming decade in the field of imaging and advanced technology for gastrointestinal neoplasia. In this overview, we summarize the salient results of that symposium. The initial sections discuss the major technologies in each area of endoluminal imaging and molecular imaging followed by applications to specific diseases such as Barrett's esophagus and colon neoplasia. Each section focuses on the current state of the art then lists major priorities for research in the field.

Endoscopic detection of early upper GI cancers

The detection of early-stage neoplastic lesions in the upper GI tract is associated with improved survival and the potential for complete endoscopic resection that is minimally invasive and less morbid than surgery. Despite technological advances in standard white-light endoscopy, the ability of the endoscopist to reliably detect dysplastic and early cancerous changes in the upper GI tract remains limited. In conditions such as Barrett's oesophagus, practice guidelines recommend periodic endoscopic surveillance with multiple biopsies, a methodology that is hindered by random sampling error, inconsistent histopathological interpretation, and delay in diagnosis. Early detection may be enhanced by several promising diagnostic modalities such as chromoendoscopy, magnification endoscopy, and optical spectroscopic/imaging techniques, as these modalities offer the potential to identify in real-time lesions that are inconspicuous under conventional endoscopy. The combination of novel diagnostic techniques and local endoscopic therapies will provide the endoscopist with much needed tools that can considerably enhance the detection and management of early stage lesions in the upper GI tract.

Optical spectroscopy for the detection of dysplasia in Barrett's esophagus

Patients with Barrett's esophagus (BE) undergo periodic endoscopic surveillance with multiple biopsy examinations in an attempt to identify dysplastic and early cancerous lesions at a time when intervention can be beneficial. However, this surveillance approach is hindered by low sampling yield, random sampling error, pathology-associated costs, and delay in diagnosis. Optical spectroscopy offers the potential to identify tissue pathology accurately in real time. The technique uses diagnostic molecular and/or microstructural information contained in light-tissue interactions such as fluorescence, elastic scattering, and inelastic (Raman) scattering. As an adjunct to endoscopy, optical spectroscopy has the capacity to enhance lesion detection in premalignant conditions such as BE. This article highlights the current status and future prospects of optical spectroscopy in BE.

Endoscopic treatment of high-grade dysplasia and early cancer in Barrett's oesophagus

Barrett's oesophagus is the premalignant precursor of oesophageal adenocarcinoma. Non-dysplastic metaplasia can progress to low-grade dysplasia, high-grade dysplasia, and finally to invasive cancer. Although the frequency of adenocarcinoma in patients with Barrett's oesophagus is low, surveillance is justified because the outcome of adenocarcinoma is poor. Oesophagectomy remains the standard treatment for patients with high-grade dysplasia and superficial carcinoma. However, it has been associated with substantial morbidity and mortality and some patients are judged unfit for surgery. In this review, the present status of less invasive procedures is discussed. Endotherapy preserves the integrity of the oesophagus and allows a better quality of life to patients at low risk of developing lymph-node metastases. Opposition to endoscopic treatment is based mainly on the identification of undetected foci of cancer and high-grade dysplasia in oesophagectomy samples. The current ablative techniques used are photodynamic therapy, argon plasma coagulation, laser treatment, and endoscopic mucosal resection.

The combined use of fluorescence, reflectance, and light-scattering spectroscopy for evaluating dysplasia in Barrett's esophagus

Intrinsic fluorescence, diffuse reflectance, and light-scattering spectroscopy provide complementary information on biochemical and morphologic information extending potentially from the molecular to the tissue level. Model-based spectral analysis in each case yields results about specific tissue parameters in a quantitative manner.Preliminary studies demonstrate that these parameters can be used for the development of algorithms that can detect dysplastic changes in patients with Barrett's esophagus (BE) with high sensitivity and specificity. Studies validating tri-modal spectroscopy based algorithms and real-time spectroscopic data analysis are under way to provide a more accurate and extensive assessment of the potential of this approach as a clinical noninvasive tool that could improve the management and treatment of BE dysplasia.

Optical detection and eradication of dysplastic Barrett's esophagus

Dysplastic Barrett's esophagus is a condition that offers multiple diagnostic and therapeutic challenges. The diagnosis of dysplasia within Barrett's esophagus currently relies on periodic endoscopic surveillance with multiple biopsies, a methodology limited by random sampling error, inconsistent histopathologic interpretation and delay in diagnosis. Optical spectroscopic and imaging techniques have the potential to identify dysplastic or early neoplastic lesions in real-time. These diagnostic modalities are needed to enhance the endoscopic surveillance of Barrett's esophagus in the future as well as help to define lesions for endoscopic therapy. Esophagectomy has been the standard of care for Barrett's esophagus with high-grade dysplasia although it is a procedure associated with significant morbidity and mortality. Minimally invasive endoscopic ablative therapies are attractive and less morbid alternatives to esophagectomy, with promising results obtained from the use of light-activated drugs (i.e., photodynamic therapy). The combination of novel optical diagnostic techniques and therapies will provide the endoscopist with much needed tools that can considerably enhance the management of patients with Barrett's esophagus. This article reviews the current status and future prospects of optical-based modalities for diagnosis and therapy of dysplastic Barrett's esophagus.