samples and subsequent histopathological analysis are frequently required for
confirmation. Due to these limitations, newer optical imaging technologies are
coming to the forefront to improve both the utility and versatility of endoscopy as
a diagnostic technique.
Visible-Spectrum Modalities Several visible-spectrum optical imaging technologies have emerged with the aim of improving the accuracy, sensitivity, and specificity of WLE. The most widely used, chromoendoscopy, utilizes the administration
of colored dyes as contrast agents to provide differentiating contrast to specific
tissues and anatomical structures. A wide variety of application-specific dyes can
be used for chromoendoscopic procedures. Administered dyes can be absorptive to
specific epithelia or tissue types (e.g., methylene blue with upper gastrointestinal
endoscopy for detection of Barrett’s esophagus), non-absorptive to highlight extracellular structure and tissue topography (e.g., indigo carmine with colonoscopy for
detection of colon polyps), or reactive to detect specific biochemical processes (e.g.,
phenol red with gastroendoscopy to visualize gastric Helicobacter pylori infection).
A key advantage of this method is that it does not require the purchase of expensive
specialized endoscopes, but rather can be performed with existing WLE equipment.
However, it does require patient administration of contrast dyes, which can be
unpleasant and invasive, and/or carry the risk of potential side effects. Furthermore,
many chromoendoscopic procedures require removal of mucus in the region of
interest prior to application of the contrast dyes, increasing the clinical time, complexity, and cost of the procedure.
Narrowband imaging (NBI) is a newer technology based on visible-spectrum
light, in which white endoscopic illumination light is filtered into specific wavelengths, typically at 415 nm (blue light) and/or 540 nm (green light). These light
bands correspond to the optimal absorptive wavelengths of hemoglobin contained in
shallow mucosal blood vessels or deeper basal layer blood vessels, respectively. NBI
endoscopy therefore enhances the optical contrast of blood vasculature over conventional WLE without requiring the administration of contrast agents (Fig. 1a). It
can be useful for improving visual identification of vascular abnormalities that are
associated with disease conditions, such as neoplasia. However, performing NBI
endoscopy requires the purchase of NBI-capable endoscope systems.
So-called “digital endoscopy” procedures utilize legacy WLE equipment with the
addition of software-based image post-processing to improve the quality of endoscopic images and provide more relevant information to clinicians. Post-processing
is flexible and can be applied to conventional WLE, NBI, or chromoendoscopic
procedures (Fig. 1b). Software suites available for this purpose include Fuji Intelligent Chromo Endoscopy (FICE) by Fujinon Corporation (Saitama, Japan) and
Pentax i-SCAN by HOYA Corporation (Tokyo, Japan.) Usage of these software
suites has shown some benefits in certain clinical diagnostic applications, but
comparative results have generally been mixed. The i-SCAN suite has been shown
to improve diagnosis of esophagitis when coupled with WLE versus WLE alone [6];
however, it also failed to show significant improvement in diagnosis of gastric
neoplasia or small adenomatous colon polyps [7, 8]. Similarly, FICE software has
The Present and Future of Optical Imaging Technologies in the Clinic:. . .
205
confirmation. Due to these limitations, newer optical imaging technologies are
coming to the forefront to improve both the utility and versatility of endoscopy as
a diagnostic technique.
Visible-Spectrum Modalities Several visible-spectrum optical imaging technologies have emerged with the aim of improving the accuracy, sensitivity, and specificity of WLE. The most widely used, chromoendoscopy, utilizes the administration
of colored dyes as contrast agents to provide differentiating contrast to specific
tissues and anatomical structures. A wide variety of application-specific dyes can
be used for chromoendoscopic procedures. Administered dyes can be absorptive to
specific epithelia or tissue types (e.g., methylene blue with upper gastrointestinal
endoscopy for detection of Barrett’s esophagus), non-absorptive to highlight extracellular structure and tissue topography (e.g., indigo carmine with colonoscopy for
detection of colon polyps), or reactive to detect specific biochemical processes (e.g.,
phenol red with gastroendoscopy to visualize gastric Helicobacter pylori infection).
A key advantage of this method is that it does not require the purchase of expensive
specialized endoscopes, but rather can be performed with existing WLE equipment.
However, it does require patient administration of contrast dyes, which can be
unpleasant and invasive, and/or carry the risk of potential side effects. Furthermore,
many chromoendoscopic procedures require removal of mucus in the region of
interest prior to application of the contrast dyes, increasing the clinical time, complexity, and cost of the procedure.
Narrowband imaging (NBI) is a newer technology based on visible-spectrum
light, in which white endoscopic illumination light is filtered into specific wavelengths, typically at 415 nm (blue light) and/or 540 nm (green light). These light
bands correspond to the optimal absorptive wavelengths of hemoglobin contained in
shallow mucosal blood vessels or deeper basal layer blood vessels, respectively. NBI
endoscopy therefore enhances the optical contrast of blood vasculature over conventional WLE without requiring the administration of contrast agents (Fig. 1a). It
can be useful for improving visual identification of vascular abnormalities that are
associated with disease conditions, such as neoplasia. However, performing NBI
endoscopy requires the purchase of NBI-capable endoscope systems.
So-called “digital endoscopy” procedures utilize legacy WLE equipment with the
addition of software-based image post-processing to improve the quality of endoscopic images and provide more relevant information to clinicians. Post-processing
is flexible and can be applied to conventional WLE, NBI, or chromoendoscopic
procedures (Fig. 1b). Software suites available for this purpose include Fuji Intelligent Chromo Endoscopy (FICE) by Fujinon Corporation (Saitama, Japan) and
Pentax i-SCAN by HOYA Corporation (Tokyo, Japan.) Usage of these software
suites has shown some benefits in certain clinical diagnostic applications, but
comparative results have generally been mixed. The i-SCAN suite has been shown
to improve diagnosis of esophagitis when coupled with WLE versus WLE alone [6];
however, it also failed to show significant improvement in diagnosis of gastric
neoplasia or small adenomatous colon polyps [7, 8]. Similarly, FICE software has
The Present and Future of Optical Imaging Technologies in the Clinic:. . .
205