In vivo identification of colonic dysplasia using fluorescence endoscopic imaging

Detection of high-grade dysplasia in Barrett's esophagus by spectroscopy measurement of 5-aminolevulinic acid-induced protoporphyrin IX fluorescence

BACKGROUND

Preliminary studies with qualitative detection methods suggest that 5-aminolevulinic acid-induced protoporphyrin IX fluorescence might improve the detection of dysplastic Barrett's epithelium. This study used quantitative methods to determine whether aminolevulinic acid-induced protoporphyrin IX fluorescence can differentiate between Barrett's mucosa with and without dysplasia.

METHODS

Patients were given 10 mg/kg of aminolevulinic acid orally 3 hours before endoscopy. Quantitative fluorescence spectra were acquired by using a nitrogen-pumped dye laser (l 400 nm) spectrograph system. The protoporphyrin IX fluorescence intensity at 635 nm was compared with the histopathologic diagnosis for mucosal biopsy specimens taken immediately after the fluorescence measurements.

RESULTS

Ninety-seven spectra were obtained from 20 patients. The mean (+/- standard error) standardized protoporphyrin IX fluorescence intensity was significantly greater (p < 0.05) for high-grade dysplastic Barrett's epithelium (0.29 +/- 0.07, n = 13) than for nondysplastic Barrett's epithelium (0.11 +/- 0.02, n = 43). By using protoporphyrin IX fluorescence alone, high-grade dysplasia was distinguished from nondysplastic tissue types with 77% sensitivity and 71% specificity. Decreased autofluorescence was particularly found in nodular high-grade dysplasia. By using the fluorescence intensity ratio of 635 nm/480 nm, nodular high-grade dysplasia could be differentiated from nondysplastic tissue with 100% sensitivity and 100% specificity.

CONCLUSION

Protoporphyrin IX fluorescence may be useful for identifying areas of high-grade dysplasia in Barrett's esophagus and for targeting of biopsies.

Gastrointestinal epithelial dysplasia: detection with new endoscopic techniques

Endoscopic detection of dysplasia currently requires either the presence of a visible lesion (such as a polyp) or the serendipitous sampling of a dysplastic focus during "blind" surveillance biopsies. To accurately and efficiently examine large areas of mucosa during surveillance endoscopy, new methods are required to render dysplasia visible. Spectroscopy and optical coherence tomography are two technologies under active investigation for this purpose. This review presents the basic concepts behind these technologies and discusses their utility in the detection of gastrointestinal dysplasia.

Enhanced endoscopy in inflammatory bowel disease

Spectroscopy and OCT are two new methods for imaging the gastrointestinal mucosa. They both rely on the interaction of light within a tissue and have been adapted for use with endoscopes. It is unlikely that any one type of imaging modality will be able to reliably diagnose the presence of microscopic dysplasia. However, combining different methods may prove to be extremely accurate for detecting dysplasia and may therefore obviate a need for taking tissue biopsies. For instance, LSS may be most helpful in detecting early dysplasia because it is sensitive to changes in nuclear size and crowding. As more cells become dysplastic, fluorescence may play a role in defining changes in content of collagen or markers of metabolism (i.e. NADH). Finally, reflectance spectroscopy becomes useful in detecting characteristic changes in the tissue architecture as dysplasia progresses to invasive cancer. Using all three types of spectroscopy at once ("tri-modal spectroscopy") has proven to be extremely accurate for classifying Barrett's mucosa as either dysplastic or nondysplastic [9]. Our current method for detecting microscopic dysplasia relies upon random biopsies and interpretation of histology by pathologists. Interobserver agreement among even experienced pathologists regarding the presence or absence and degree of dysplasia in histologic specimens is not consistent [50]. Spectroscopy and OCT may ultimately provide new methods for accurately diagnosing dysplasia in real-time, without the need for tissue processing, and without the interobserver variations of histologic interpretation.

New technology in the endoscopy center

The boundaries of endoscopy will continue to expand. Imaging modalities, such as high-resolution and high magnification endoscopy, tissue spectroscopy, optical coherence tomography, and wireless endoscopy, will continue to evolve. New therapeutic modalities, such as endoscopic antireflux procedures, are making endoscopic surgery a reality. In the increasingly restrictive reimbursement environment, however, it is critical to establish the cost-effectiveness of these new technologies to integrate them into daily practice.

Detection of dysplastic intestinal adenomas using enzyme-sensing molecular beacons in mice

BACKGROUND & AIMS

Proteases play key roles in the pathogenesis of tumor growth and invasion. This study assesses the expression of cathepsin B in dysplastic adenomatous polyps.

METHODS

Aged Apc(Min/+) mice served as an experimental model for familial adenomatous polyposis. The 4 experimental groups consisted of (a) animals injected with a novel activatable, cathepsin B sensing near infrared fluorescence (NIRF) imaging probe; (b) animals injected with a nonspecific NIRF; (c) uninjected control animals; and (d) non-APC(Min/+) mice injected with the cathepsin B probe. Lesions were analyzed by immunohistochemistry, Western blotting, reverse transcription-polymerase chain reaction, and optical imaging.

RESULTS

Cathepsin B was consistently overexpressed in adenomatous polyps. When mice were injected intravenously with the cathepsin reporter probe, intestinal adenomas became highly fluorescent indicative of high cathepsin B enzyme activity. Even microscopic adenomas were readily detectable by fluorescence, but not light, imaging. The smallest lesion detectable measured 50 microm in diameter. Adenomas in the indocyanine green and/or noninjected group were only barely detectable above the background.

CONCLUSIONS

The current experimental study shows that cathepsin B is up-regulated in a mouse model of adenomatous polyposis. Cathepsin B activity can be used as a biomarker to readily identify such lesions, particularly when contrasted against normal adjacent mucosa. This detection technology can be adapted to endoscopy or tomographic optical imaging methods for screening of suspicious lesions and potentially for molecular profiling in vivo.

Relationship between depth of a target in a turbid medium and fluorescence measured by a variable-aperture method

The relationship between the depth of a target in a turbid medium and the fluorescence ratio profile measured by use of illumination and collection apertures with variable diameters and the same optical path is shown. The forward problem was studied by Monte Carlo simulations of the propagation of fluorescent light through a theoretical model of a biologically relevant system for a range of aperture diameters. The curve of the fluorescence ratio as a function of the aperture diameter is characterized by a maximum/minimum point whose position shifts linearly with the depth of the target. Furthermore, the position of the maximum/minimum is observed to be insensitive to variations in the fluorescence efficiency and to the optical properties of the target layer or the entire medium.

Fluorescence spectroscopy of epithelial tissue throughout the dysplasia-carcinoma sequence in an animal model: spectroscopic changes precede morphologic changes

BACKGROUND AND OBJECTIVE

The hamster cheek pouch carcinogenesis model, using chronic treatments of dimethylbenz[alpha]anthracene (DMBA) was used as a model system to investigate changes in epithelial tissue autofluorescence throughout the dysplasia-carcinoma sequence.

STUDY DESIGN/MATERIALS AND METHODS

Fluorescence emission spectra were measured weekly from 42 DMBA-treated animals and 20 control animals at 337, 380, and 460 nm excitation. A subset of data in which histopathology was available was used to develop diagnostic algorithms to separate neoplastic and non-neoplastic tissue. The change in fluorescence intensity over time was examined in all samples at excitation-emission wavelength pairs identified as diagnostically useful.

RESULTS

Algorithms based on autofluorescence can separate neoplastic and non-neoplastic tissue with 95% sensitivity and 93% specificity. Greatest contributions to diagnostic algorithms are obtained at 380 nm excitation, and 430, 470, and 600 nm emission. Changes in fluorescence intensity are apparent as early as 3 weeks after initial treatment with DMBA, whereas morphologic changes associated with dysplasia occur on average at 7.5-12.5 weeks after initial treatment.

CONCLUSIONS

Fluorescence spectroscopy provides a potential tool to identify biochemical changes associated with dysplasia and hyperplasia, which precede morphologic changes observed in histologically stained sections.

Fast and noninvasive fluorescence imaging of biological tissues in vivo using a flying-spot scanner

We have developed a flying-spot scanner (FSS), for fluorescence imaging of tissues in vivo. The FSS is based on the principles of single-pixel illumination and detection via a raster scanning technique. The principal components of the scanner are a laser light source, a pair of horizontal and vertical scanning mirrors to deflect the laser light in these respective directions on the tissue surface, and a photo multiplier tube (PMT) detector. This paper characterizes the performance of the FSS for fluorescence imaging of tissues in vivo. First, a signal-to-noise ratio (SNR) analysis is presented. This is followed by characterization of the experimental SNR, linearity and spatial resolution of the FSS. Finally, the feasibility of tissue fluorescence imaging is demonstrated using an animal model. In summary, the performance of the FSS is comparable to that of fluorescence-imaging systems based on multipixel illumination and detection. The primary advantage of the FSS is the order-of-magnitude reduction in the cost of the light source and detector. However, the primary disadvantage of the FSS its significantly slower frame rate (1 Hz). In applications where high frame rates are not critical, the FSS will represent a low-cost alternative to multichannel fluorescence imaging-systems.

Autofluorescence endoscopy: feasibility of detection of GI neoplasms unapparent to white light endoscopy with an evolving technology

BACKGROUND

Case studies are presented of fluorescence endoscopy in the upper and lower GI tract to illustrate the ability to detect early-stage lesions that were not observable with white light endoscopy or those in which the assessment of the stage or extension of the lesion were equivocal.

METHODS

A new fluorescence imaging system was used in which blue light excites the naturally-occurring fluorescence of tissues (autofluorescence). The system produces real-time, false-color images that combine green and red fluorescence intensities. In general, abnormal lesions are seen to have an increase in the red-to-green fluorescence intensity compared with surrounding tissue. This system was evaluated in patients at 4 participating institutions, concurrently with standard white light endoscopy, with or without dye staining.

RESULTS

Selected cases are presented in which fluorescence imaging identified specific lesions including focal high-grade dysplasia in Barrett's mucosa, signet ring carcinoma of the stomach, and flat adenoma in the colon.

CONCLUSIONS

The capability of autofluorescence endoscopy to detect the presence and extent of occult malignant and premalignant GI lesions has been demonstrated. The future development and evaluation of this technology are discussed.

Potential new endoscopic techniques for the earlier diagnosis of pre-malignancy

Light interacts with tissue in a variety of ways, including absorption, fluorescence, elastic scattering and Raman scattering. These interactions enable a number of promising technologies for endoscopic diagnosis of pre-malignancy, including chromoscopy; fluorescence, scattering and Raman spectroscopies; and optical coherence tomography. Although still in various stages of technical development and clinical trials, these optical diagnostic techniques are demonstrating strong potential to significantly enhance the clinical endoscopist's ability to detect dysplasia in gastrointestinal mucosae.

Optimal fluorescence excitation wavelengths for detection of squamous intra-epithelial neoplasia: results from an animal model

Using the hamster cheek pouch carcinogenesis model, we explore which fluorescence excitation wavelengths are useful for the detection of neoplasia. 42 hamsters were treated with DMBA to induce carcinogenesis, and 20 control animals were treated only with mineral oil. Fluorescence excitation emission matrices were measured from the cheek pouches of the hamsters weekly. Results showed increased fluorescence near 350-370 nm and 410 nm excitation and decreased fluorescence near 450-470 nm excitation with neoplasia. The optimal diagnostic excitation wavelengths identified using this model - 350-370 nm excitation and 400-450 nm excitation - are similar to those identified for detection of human oral cavity neoplasia.

Endoscopic detection of dysplasia in patients with Barrett's esophagus using light-scattering spectroscopy

BACKGROUND & AIMS

We conducted a study to assess the potential of light-scattering spectroscopy (LSS), which can measure epithelial nuclear enlargement and crowding, for in situ detection of dysplasia in patients with Barrett's esophagus.

METHODS

Consecutive patients with suspected Barrett's esophagus underwent endoscopy and systematic biopsy. Before biopsy, each site was sampled by LSS using a fiberoptic probe. Diffusely reflected white light was spectrally analyzed to obtain the size distribution of cell nuclei in the mucosal layer, from which the percentage of enlarged nuclei and the degree of crowding were determined. Dysplasia was assigned if more than 30% of the nuclei exceeded 10 microm and the histologic findings compared with those of 4 pathologists blinded to the light-scattering assessment. The data were then retrospectively analyzed to further explore the diagnostic potential of LSS.

RESULTS

Seventy-six sites from 13 patients were sampled. All abnormal sites and a random sample of nondysplastic sites were reviewed by the pathologists. The average diagnoses were 4 sites from 4 different patients as high-grade dysplasia (HGD), 8 sites from 5 different patients as low-grade dysplasia (LGD), 12 as indefinite for dysplasia, and 52 as nondysplastic Barrett's. The sensitivity and specificity of LSS for detecting dysplasia (either LGD or HGD) were 90% and 90%, respectively, with all HGD and 87% of LGD sites correctly classified. Decision algorithms using both nuclear enlargement and crowding further improved diagnostic accuracy, and accurately classified samples into the 4 histologic categories.

CONCLUSIONS

LSS can reliably detect LGD and HGD in patients with Barrett's esophagus.

Fluorescence spectroscopy of neoplastic and non-neoplastic tissues

Fast and non-invasive, diagnostic techniques based on fluorescence spectroscopy have the potential to link the biochemical and morphologic properties of tissues to individual patient care. One of the most widely explored applications of fluorescence spectroscopy is the detection of endoscopically invisible, early neoplastic growth in epithelial tissue sites. Currently, there are no effective diagnostic techniques for these early tissue transformations. If fluorescence spectroscopy can be applied successfully as a diagnostic technique in this clinical context, it may increase the potential for curative treatment, and thus, reduce complications and health care costs. Steady-state, fluorescence measurements from small tissue regions as well as relatively large tissue fields have been performed. To a much lesser extent, time-resolved, fluorescence measurements have also been explored for tissue characterization. Furthermore, sources of both intrinsic (endogenous fluorophores) and extrinsic fluorescence (exogenous fluorophores) have been considered. The goal of the current report is to provide a comprehensive review on steady-state and time-resolved, fluorescence measurements of neoplastic and non-neoplastic, biologic systems of varying degrees of complexity. First, the principles and methodology of fluorescence spectroscopy are discussed. Next, the endogenous fluorescence properties of cells, frozen tissue sections and excised and intact bulk tissues are presented; fluorescence measurements from both animal and human tissue models are discussed. This is concluded with future perspectives.