Gastrointestinal Endoscopy
Volume 70, Issue 1 , Pages 7-8, July 2009

Search for premalignant mucosal lesions: does endoscopic measurement of oxygen saturation by differential path-length spectroscopy help?

Sepulveda Ambulatory Care Center, Veterans Affairs Greater Los Angeles Healthcare System, North Hills, California, USA

Division of Gastroenterology, Department of Medicine, David Geffen School of Medicine at University of California Los Angeles, Los Angeles, California, USA

Article Outline

Abbreviations: DPS, differential path-length spectroscopy, NBI, narrow-band imaging

 

Microvascular oxygen saturation remains high (∼90%) throughout the metaplasia-dysplasia-adenocarcinoma sequence of Barrett's esophagus.

The potential to improve survival and quality of life has motivated investigators to study endoscopic methods for the detection of premalignant lesions,1 and in this endeavor, even small improvements in our technological understanding are welcome.2 The article by Amelink et al3 in the current issue of Gastrointestinal Endoscopy showing data derived from differential path-length spectroscopy (DPS) supporting the design of narrow-band imaging (NBI) technology illustrates these 2 phenomena quite well.

Their article describes the endoscopic noninvasive measurement of the oxygen saturation of the microvascular blood in Barrett's dysplasia by optical spectroscopy.3 Recently, endoscopic screening for the early detection of Barrett's esophageal adenocarcinoma has been focused on visualization of the microvascular morphology by using NBI.4 The NBI technique is designed to detect increased contrast in the endoscopic images distinguishing dysplastic from normal mucosal surfaces based on the detection of oxyhemoglobin with high oxygen saturation. Amelink et al3 hypothesized that adjustment of the center wavelength of the NBI blue imaging filter based on knowledge of the microvascular blood oxygen saturation of dysplastic and early cancerous Barrett's mucosa may lead to improved image contrast. They performed in vivo, noninvasive endoscopic measurements of the microvascular oxygen saturation of different pathologic grades of Barrett's mucosa by using DPS. Measurements were made on normal (n = 7), low-grade dysplastic (n = 10), high-grade dysplastic (n = 7), and cancerous (n = 4) Barrett's mucosa by using a fiberoptic probe and were correlated with the histological results of biopsy specimens taken from the same location. They found that microvascular oxygen saturation remained high (∼90%) throughout the metaplasia-dysplasia–adenocarcinoma sequence. The inference is that the visual difference demonstrated by NBI technology between normal, premalignant, and malignant tissue is optimal. They concluded that the NBI blue imaging filter, centered on the peak absorption of oxyhemoglobin (415 nm), is well chosen, and little improvement in image contrast is to be expected from changes in this center wavelength.

The authors also discussed the difference between earlier reports claiming increased expression of hypoxia-inducible proteins (markers of decreased tissue blood flow and oxygenation) in premalignant and malignant Barrett's tissues and their finding of high oxygen saturation, even in the esophageal adenocarcinoma in their subjects. Increased tissue extraction of oxygen by the cancer was invoked as a possible explanation for the discrepancy. Part of the difficulty in appreciating some of the concepts espoused in this article is the fact that the authors did not provide in vivo validations of the DPS measurements in tissues. In this report, DPS was presented primarily as a product derived from theoretical manipulations of reflected light without reference to traditionally accepted measurements of tissue oxygen tension, tissue oxygen saturation, or tissue blood flow in GI tissues. Instead, validation was performed by correlating DPS measurements with the oxygen dissociation curve in optical phantoms. The deviation between the DPS-extracted oxygen saturation and the theoretical oxygen saturation of the blood according to the oxygen dissociation curve was less than 3% over the entire range of saturations (5%-100%). Thus, all in vivo factors that might alter DPS measurements were excluded. It is not unreasonable for a clinician to expect measurements derived from complicated equations to be compared with some form of physiologic data to validate the claims. For instance, the authors made no attempt to show that the DPS method, as applied, could detect decreased oxygen saturation in tissues in vivo. Two other methods, namely, reflectance spectrophotometry and visible light spectroscopy, have been described to provide endoscopic measurement of oxygen saturation in GI tissues.5 Comparison of data in tissues in vivo obtained with the DPS technique and with these previously described endoscopic methods might be instructive.

In the case of DSP technology, whether it will have a role in clinical practice is uncertain. DPS may join the ranks of laser-induced fluorescence spectroscopy,6 light-scattering spectroscopy and optical coherence tomography,7 in vivo near-infrared Raman spectroscopy,8 5-aminolevulinic acid-induced protoporphyrin IX,9 light-induced autofluorescence spectroscopy,1 temporal and spectral fluorescence spectroscopy,10 optical parametric oscillator laser excitation,11 visible light tissue oximetry,12 laser-scanning confocal microscopy and endocytoscopy,13 and other novel developments in providing a promising future in the search for premalignant mucosal lesions by endoscopic methods. These novel techniques have attracted considerable attention among enthusiasts,14 but their clinical significance, including NBI,4 in effectively reducing mortality and morbidity of GI malignancies remains to be established. Conscientious investigators should exercise prudence in cautioning readers that these diligent investigative efforts may have unintended consequences. Experts frequently recommend incorporation of advances in technology to diagnose premalignant lesions in routine clinical practice. However, if adopted prematurely before proven effective treatment is available, these novel procedures may increase the cost of health care without therapeutic benefits for the patients and may raise undue anxiety in high-risk individuals.

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Disclosure 

The author disclosed no financial relationships relevant to this publication. Supported in part by VA Clinical Merit Medical Research Funds and the American Society for Gastrointestinal Endoscopy Career Development Award (FWL 1985).

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References 

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PII: S0016-5107(08)02903-9

doi:10.1016/j.gie.2008.11.015

Gastrointestinal Endoscopy
Volume 70, Issue 1 , Pages 7-8, July 2009

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