self-contained capsule-shaped module has been developed for esophageal OCT; the
“capsule” is swallowed by a fully conscious patient and then recovered via a narrow
tethering fiber. This development raises the possibility of esophageal endoscopy
without the need for sedation, which is a significant barrier to early screening of
Barrett’s esophagus [17].
Multimodal Imaging Despite advances in imaging technology, all endoscopic
imaging modalities are constrained by inherent physical or technical limitations
which limit clinical usefulness. To overcome this, different imaging modalities
could be combined together into a single endoscopic procedure, with the ultimate
goal of mitigating the shortcomings in one imaging modality by supplementing it
with others that are not subject to the same disadvantages. Aside from the use of
wide-field WLE, which is routinely used in conjunction with other endoscopic
modalities (e.g., to guide magnification endoscopy techniques such as CLEM),
multimodal endoscopic imaging is mostly at the investigative stage. Several novel
applications have been demonstrated in clinical pilot studies; for example, a trimodal
endoscope was devised to combine WLE, NBI, and AFI to reduce the high falsepositive rate associated with AFI colonoscopy in screening for colorectal adenomas
and for gastric neoplasia [11, 18]; in another study, OCT was combined with WLE
and IFE cystoscopy (with hexaminolevulinate) to reduce false positives in the
diagnosis of urothelial carcinoma [15].
Preclinical Modality Pipeline A number of promising new optical imaging technologies are being evaluated for endoscopic applications.
Raman spectroscopy, an imaging technique which relies upon inelastic scattering
of laser light to detect differences in vibrational or rotational molecular states, has
been investigated for in vivo imaging systems, including endoscopy. Raman spectroscopy is particularly notable for its chemical specificity, which is useful for
measuring biochemical states and changes in biological tissue. It can be combined
with far-red or near-infrared light sources for deep tissue penetration. Though
promising, Raman spectroscopic endoscopy and other Raman-based imaging
methods thus far have faced technical obstacles, primarily due to the low intensity
of inelastic light scattering signatures, which limit the accuracy and speed of image
acquisition compared to existing clinical modalities. A variety of innovative Ramanbased imaging technologies have been developed to overcome these limitations,
such as selective-sampling Raman spectroscopy, coherent anti-Stokes Raman spectroscopy, surface-enhanced Raman spectroscopy, and spatially offset Raman
spectroscopy. Endoscopic Raman spectroscopy has been evaluated in patient feasibility studies for a variety of applications, including colonoscopic identification of
precancerous adenomatous polyps, endoscopic diagnosis of gastric dysplasia, and
detection of nasopharyngeal cancers [19–21].
Cerenkov luminescence (CL), light emissions caused by the transit of charged
particle radiation through a dielectric medium at greater than the speed of light, has
been evaluated for medical imaging purposes. The resultant technology, called
Cerenkov luminescence imaging (CLI), utilizes Cerenkov light generated by the
decay of an injected β particle-emitting isotope, which are typically used to provide
The Present and Future of Optical Imaging Technologies in the Clinic:. . .
209
“capsule” is swallowed by a fully conscious patient and then recovered via a narrow
tethering fiber. This development raises the possibility of esophageal endoscopy
without the need for sedation, which is a significant barrier to early screening of
Barrett’s esophagus [17].
Multimodal Imaging Despite advances in imaging technology, all endoscopic
imaging modalities are constrained by inherent physical or technical limitations
which limit clinical usefulness. To overcome this, different imaging modalities
could be combined together into a single endoscopic procedure, with the ultimate
goal of mitigating the shortcomings in one imaging modality by supplementing it
with others that are not subject to the same disadvantages. Aside from the use of
wide-field WLE, which is routinely used in conjunction with other endoscopic
modalities (e.g., to guide magnification endoscopy techniques such as CLEM),
multimodal endoscopic imaging is mostly at the investigative stage. Several novel
applications have been demonstrated in clinical pilot studies; for example, a trimodal
endoscope was devised to combine WLE, NBI, and AFI to reduce the high falsepositive rate associated with AFI colonoscopy in screening for colorectal adenomas
and for gastric neoplasia [11, 18]; in another study, OCT was combined with WLE
and IFE cystoscopy (with hexaminolevulinate) to reduce false positives in the
diagnosis of urothelial carcinoma [15].
Preclinical Modality Pipeline A number of promising new optical imaging technologies are being evaluated for endoscopic applications.
Raman spectroscopy, an imaging technique which relies upon inelastic scattering
of laser light to detect differences in vibrational or rotational molecular states, has
been investigated for in vivo imaging systems, including endoscopy. Raman spectroscopy is particularly notable for its chemical specificity, which is useful for
measuring biochemical states and changes in biological tissue. It can be combined
with far-red or near-infrared light sources for deep tissue penetration. Though
promising, Raman spectroscopic endoscopy and other Raman-based imaging
methods thus far have faced technical obstacles, primarily due to the low intensity
of inelastic light scattering signatures, which limit the accuracy and speed of image
acquisition compared to existing clinical modalities. A variety of innovative Ramanbased imaging technologies have been developed to overcome these limitations,
such as selective-sampling Raman spectroscopy, coherent anti-Stokes Raman spectroscopy, surface-enhanced Raman spectroscopy, and spatially offset Raman
spectroscopy. Endoscopic Raman spectroscopy has been evaluated in patient feasibility studies for a variety of applications, including colonoscopic identification of
precancerous adenomatous polyps, endoscopic diagnosis of gastric dysplasia, and
detection of nasopharyngeal cancers [19–21].
Cerenkov luminescence (CL), light emissions caused by the transit of charged
particle radiation through a dielectric medium at greater than the speed of light, has
been evaluated for medical imaging purposes. The resultant technology, called
Cerenkov luminescence imaging (CLI), utilizes Cerenkov light generated by the
decay of an injected β particle-emitting isotope, which are typically used to provide
The Present and Future of Optical Imaging Technologies in the Clinic:. . .
209