Abstract
Increase in abnormal microvessels in the superficial mucosa is often relevant to diagnostic findings of neoplasia in digestive endoscopy; hence, observation of superficial vasculature is crucial for cancer diagnosis. To enhance the appearance of such vessels, several spectral endoscopic imaging techniques have been developed, such as narrow-band imaging and blue laser imaging. Both techniques exploit narrow-band blue light for the enhancement. The emergence of such spectral imaging techniques has increased the importance of understanding the relation of the light wavelength to the appearance of superficial vasculature, and thus a new method is desired for quantitative analysis of vessel visibility in relation to the actual structure in the tissue. Here, we developed microvessel-simulating phantoms that allowed quantitative evaluation of the appearance of 15-μm-thick vessels. We investigated the relation between the vascular contrast and light wavelength by the phantom measurements and also verified it in experiments with swine, where the endoscopically observed vascular contrast was investigated together with its real vascular depth and diameter obtained by microscopic observation of fluorescence-labeled vessels. Our study indicates that changing the spectral property even in the wavelength range of blue light may allow selective enhancement of the vascular depth for clinical use.
Highlights
In digestive endoscopy, it is well known that the emergence of microvessels in the superficial layer of the mucosa is an important aspect of cancerous disease
3.2 Results We classified the vessels that appeared in the endoscopic images by their depths and diameters into the three types presented in Table 1 and calculated the mean vascular contrasts for each type
The vascular contrasts were matched with high precision for two types of vessel with different optical parameters (Fig. 7)
Summary
It is well known that the emergence of microvessels in the superficial layer of the mucosa is an important aspect of cancerous disease. Short-wavelength light sources are utilized in spectral endoscopy techniques. The absorption coefficient (μa) of blood is large at short wavelengths [Fig. 1(a)]. The absorption coefficient of blood μa at 420 nm is more than six times greater than that at 540 nm. This large absorption of light leads to high vascular contrast even for thin vessels including microvessels. The scattering coefficient of mucosa is large at short wavelengths.
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