A Prospective Randomized Study of Colonoscopy Using Blue Laser Imaging and White Light Imaging in the Detection and Differentiation of Colonic Polyps

BACKGROUND The adenoma detection rate by colonoscopy for asymptomatic individuals aged 50 years and older is estimated to be at least 25%. It is known that during colonoscopy, lesions may be missed. The miss rates for lesions depend on its size. In a meta-analysis, the overall miss rates for colonic polyps of any size was 22% (95% confidence interval [CI]: 19 - 26%) but based on size of adenomas, the miss rates ranged from 26% (95% CI: 21 - 30%) for lesions 1 - 5mm, to 13% (95% CI: 8 - 20%) for lesions 5 - 9mm and 2 (95% CI: 1 - 8%) for lesions larger than 10mm. Factors implicated in missed lesions include poor bowel preparation, short withdrawal time, lack of meticulous examination, and possibly subtle mucosal changes, especially for small or flat adenomas, that may be easily missed on white light imaging (WLI).

Image enhanced endoscopy techniques have been evaluated for the detection and differentiation of colonic polyps. Narrow band imaging (NBI), developed by Olympus Corporation (Tokyo, Japan) is one such technique and is a function available in all colonoscopies as a press button. When NBI is activated, an optical filter is applied to the white light source, such that only the narrow bandwidths of blue (440 - 460 nm) and green (540 - 560 nm) wavelengths are transmitted. These narrow bandwidths enhance the visualization of blood vessels and mucosal pit patterns. This technique has been shown to be useful in predicting colonic polyp histology and depth of mucosal invasion in the context of intra-mucosal cancer. The two common classification systems used predict histology is the NICE and the Sano classification. The NICE classification can be used without optical magnification; it evaluates the color of the lesion, regularity of the overlying vessels and regularity of the surface pattern. The Sano classification requires optical magnification in order to assess the capillary patterns such as whether there is dilation, irregularity or loss of irregular capillaries over the lesion. In the context of adenoma detection, the results are more contentious. A meta-analysis of randomized studies examining the utility of the first generation NBI system when compared to high definition WLI showed no difference in detection rates; it was only superior when compared to non high definition WLI, which may not be so relevant now since most new systems use high definition WLI. A criticism of the NBI system had been the dark endoscopic view; this is a result of the optical filter, and can limit the far view. A second generation NBI system has since been developed. It is characterized by much brighter illumination despite the optical filter, and thus the far view is improved. A recent randomized controlled study compared the second-generation NBI system with high definition WLI. NBI was shown to improve polyp and adenoma detection rates compared to WLI (adenoma: 48.3% vs. 34.4%, p = 0.01; polyps: 61.1% vs. 48.3%, p = 0.02).

Blue laser imaging (BLI) is another form of narrow bandwidth imaging developed by Fujifilm Corporation (Tokyo, Japan). It is a function integrated into the colonoscopy systems and can be activated and alternated with white light endoscopy by a push button. There is also optical magnification capability, thereby allowing detailed examination of micro-surface and micro-capillary structures. Instead of using an optical filter for white light to produce narrow bandwidths, the BLI system has a unique feature of illumination using two lasers and a white light phosphor to accomplish the visual enhancement of surface vessels and structures. A laser with a wavelength of 450nm stimulates the phosphor to irradiate a white-color illumination. The other laser, with a wavelength of 410nm, is used to enhance the blood vessels at shallow depth in the mucosa. Early data has shown its usefulness in predicting the histology of mucosal lesions. A comparative study showed that BLI had a greater far view compared to NBI due to its much brighter illumination. Thus far there has been no study to determine whether the use of BLI will increase the detection rate of colonic polyps and adenomas when compared to WLE. In addition, there has been no prior study of applying the NICE and Sano classifications developed using NBI to BLI. Recently in Japan a workgroup has proposed the JNET classification system to characterize polyps. This has not been applied using the BLI system either, being developed under NBI. Similar to Sano classification, this uses optical magnification. The main difference between the JNET and San classification systems is that in JNET classification system, Sano 2 is named JNET 2A, and Sano 3A is subsumed under JNET 2B, and Sano 3A becomes JNET 3.

AIM This study aims to determine whether BLI can increase the detection rate of colonic polyps and adenomas when compared to white light endoscopy, with the null hypothesis being no difference in detection rates. This study will also examine the use of NICE and Sano and JNET classification systems to predict histology with the BLI system.

METHODS This is a prospective randomized controlled study. Patients will be randomized in a 1:1 ratio in blocks of 10 to undergo either BLI or WLI colonoscopy. Randomization will be carried out by computer-generated random sequences. Once informed consent is obtained, the research assistant will disclose the assigned imaging technique (BLI or WLI) to the responsible endoscopist before the procedure.