Biomedical Engineering Reference
In-Depth Information
the emission filter may need to be moved out of the detection path when capturing
reflectance image. This is the case, for example, when the excitation spectrum is
wide and within the spectrum for reflectance imaging. While the illumination paths
for two modalities are separated in Fig. 9.1 a, they can share the same illumination
path if a dichroic mirror is used to combine the light from two different light
sources or if a filter array is used to select the illumination spectrum from the same
light source.
Figure 9.1 b is a configuration for parallel imaging. Typically, two detectors
are necessary to take two images simultaneously. The reflectance signal and
fluorescence signal are separated by the dichroic beamsplitter, and an emission filter
is needed in the detection path of the fluorescence signal to block the excitation light.
One challenge of parallel imaging lies in the choice of the spectra for both imaging
modalities. The dichroic mirror separates and directs the fluorescence signal and the
reflectance signal to their corresponding detectors. When there is overlap between
the excitation light and light for reflectance imaging, or where the excitation light
is used for reflectance imaging, a neutral filter may be needed in the reflectance
imaging path to attenuate the excitation light which is usually very intense in order
to excite sufficient fluorescence response.
Douplik et al. combined autofluorescence imaging and reflectance imaging
to improve detection of dysplastic colonic lesions by capturing reflectance and
fluorescence images sequentially [ 1 ]. The multimodal endoscope increased the
detection rate of dysplastic and nondysplastic lesions by 26 and 13 %, respectively,
compared to the white light endoscope.
To remove specular reflection in the reflectance image, a multimodal imaging
system combining autofluorescence, white light reflectance, and orthogonal polar-
ization reflectance imaging modalities was demonstrated for early detection of oral
cancer [ 2 ]. The orthogonal polarization imaging removes specular reflection and
increases contrast associated with subsurface vasculature, which is often increased
in neoplastic lesions.
In order to reduce the false-positive rate, a narrowband reflectance imaging (NBI)
was integrated into an autofluorescence endoscope [ 3 ]. Autofluorescence imaging
scans large tissue surface quickly to identify possible suspicious lesions with high
sensitivity, and then NBI is used to characterize the tissue properties in detail
because NBI can provide detailed inspection of mucosal patterns for the detection
of dysplasia.
Salomatina et al. combined reflectance and fluorescence polarization imaging
with spectroscopic analysis of reflectance images for facilitating intraoperative
delineation of basal cell carcinoma (BCC) [ 4 ]. Two images were captured sequen-
tially, with one light source providing illumination for both imaging modalities
and with both imaging modalities sharing the same detection system. Reflectance
polarization imaging provides detailed information on skin morphology, and fluo-
rescence polarization imaging exhibits high contrast of cancerous tissue. The optical
densities and their wavelength derivatives for tumor and normal tissues can be used
for intraoperative cancer delineation.
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