With learning curve, narrow-band imaging comparable to white light colonoscopy

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In comparing narrow-band imaging (NBI) without high magnification to standard white light colonoscopy in differentiating colorectal polyps during real-time colonoscopy, NBI performed better than white light colonoscopy, but only after endoscopists new to using it overcame a significant learning curve, according to research published in the December issue of GIE: Gastrointestinal Endoscopy.

NBI is a new optical technology that modifies white light by using only certain wavelengths to enhance the image. The technology provides more visual detail of the lining of the colon (including polyps) and of the small blood vessels near the surface of the polyps. According to the authors, at the present time, there is no widely adopted method for distinguishing between adenomatous and nonadenomatous polyps during real-time colonoscopy.

"In this prospective trial, we aimed to compare standard broadband white light colonoscopy with narrow-band imaging for the differentiation of colorectal polyps during real-time colonoscopy by using a modified Kudo pit pattern classification and vascular color intensity grading," said study lead author Jason Rogart, MD, Yale University School of Medicine in New Haven, Conn.

A total of 302 patients were enrolled from August 2006 to July 2007 at Yale; 265 polyps were found in 131 patients resulting in an adenoma detection rate of 30 percent. Of the polyps, 49 percent were adenomas or carcinomas, whereas 51 percent were nonadenomatous; 74 percent of adenomas were 5 mm or smaller, and 42 percent were 3 mm or smaller.

Four endoscopists, with a minimum number of 1,000 colonoscopies previously performed, participated in this study. The participating physicians were oriented to NBI before enrollment through a one-hour interactive lecture on NBI, instruction in classifying polyps based on the surface characteristics (simplified Kudo pit pattern and vascular color intensity grading), and a pretest that consisted of 20 unknown polyps photographed with the NBI system. Additionally, an atlas of endoscopic images of polyps examined with both chromoendoscopy and NBI were posted in the procedure areas.

According to the results, NBI accuracy was 80 percent compared with 77 percent for white light alone. NBI performed significantly better than white light in diagnosing adenomas (sensitivity 80 vs. 69 percent), particularly for adenomas ? 5 mm (75 vs. 60 percent). There was no difference between NBI and white light for nonadenomatous polyps. Diagnostic accuracies were better for larger polyps (mean size of correct prediction 4.7 mm vs. 3.9 mm) and non-significant for polypoid shape (87 vs. 79 percent for polyps with sessile shape). Compared with white light, however, NBI did not significantly improve accuracy in any size or shape category, nor for any segment of the colon.

An equal number of polyps were analyzed in each of the two study periods (133 and 132, respectively). The researchers reported that NBI accuracies significantly improved from 74 to 87 percent between the two study periods whereas, white light accuracies were unchanged (78 percent first half and 79 percent second half). In the second half of the study (i.e., after the learning curve was reached), therefore, NBI was significantly more accurate than white light.

“At the present time, current NBI accuracy rates of 80 percent are inadequate to defer polypectomy (polyp removal) and, therefore, limit the utility of NBI in evaluating colorectal polyps during routine clinical practice. Accuracy rates that approach 100 percent would be required for endoscopists to use this assessment to determine the need for polyp removal with confidence. Further investigation into superficial mucosal patterns of polyps and the optimal method of viewing them with NBI is needed,” Rogart and colleagues wrote.