Multimodal Biomedical Imaging Systems - Biomedical Optical Imaging Technologies: Design and Applications - page 300

a

b

Detectorfor reflectance
imaging

Emission
filter

Detector

Dichroic
filter

Detector for
fluorescence
imaging

Illumination unit for
fluorescence
imaging

Imaging lens
Emission filter

Imaging lens

Ilumination unit for
fluorescence
imaging

Illumination unit
for reflectance
imaging

Exitation filter

Illumination unit
for reflectance
imaging

Exitation filter

Sample

Sample

Fig. 9.1 Multimodal area imaging systems. ( a ) Sequential imaging with one detector and ( b )
parallel imaging with two detectors

9.2.1 Multimodal Area Imaging Systems

There are two commonly used area imaging techniques: reflectance imaging and
fluorescence imaging. Other area imaging techniques, such as spectral imaging,
narrowband reflectance imaging, and polarization imaging, are basically variations
of reflectance imaging. Reflectance imaging generally provides a very useful image
of surface texture but is limited to detecting lesions based on gross morphological
changes, and its sensitivity in detecting change within the tissue is generally low.
Fluorescence imaging provides biochemical and structural information of biological
specimens. It is very sensitive to early tissue transformation and offers additional
information about tissues that is not visible under conventional reflectance imaging.
However, its specificity is usually low because it is sensitive to bacteria, food, blood,
and other factors.
Because they are based on different contrast mechanisms and are sensitive to
independent morphological and/or functional markers of diseases, the combination
of fluorescence and reflectance imaging produces images that can better reveal
biochemical and morphologic alterations that characterize early neoplasia. Fluo-
rescence images and reflectance images can either be captured simultaneously or
sequentially, depending on the system configurations.
Figure 9.1 a is a configuration for sequential imaging with two imaging modalities
sharing the same imaging path. Typically, only one detector is needed; the fluores-
cence image and reflectance image are captured by turning on the light source for
each mode sequentially. When the wavelength for reflectance imaging is longer
than the excitation wavelength for fluorescence imaging, the emission filter for
fluorescence imaging can remain in the detection path. However, in some situations,