Multimodal Biomedical Imaging Systems - Biomedical Optical Imaging Technologies: Design and Applications - page 311

The configuration is the same as that used for confocal fluorescence imaging.
When the emission filter is moved out of the detection path, the captured image is
a reflectance image from the excitation light. When two detectors are used, the two
images can be obtained simultaneously, with a dichroic mirror separating light with
different wavelengths.

9.2.7.2 Multimodal Photoacoustic Systems

Photoacoustic microscopy is an optical absorption-based imaging technique that
detects laser-induced photoacoustic waves as a result of specific optical absorption.
Three-dimensional photoacoustic images of tissue are acquired with scanning of
optical illumination and ultrasonic detection. In addition to high-resolution struc-
tural information, OCT can also provide functional information about blood flow
by measuring the Doppler shift. However, imaging hemoglobin oxygen saturation
is still beyond the capability of conventional OCT.
Jiao et al. developed a multimodal imaging technique by integrating photoa-
coustic microscopy and spectral-domain OCT to acquire simultaneous volumetric
microscopic images of both optical absorption and scattering contrasts in tissue [ 33 ].
The multimodal system provides 3-D microscopic imaging of biological tissues
with complementary contrast mechanisms (optical absorption and scattering). In
the integrated system, the illumination light for two modalities is combined with a
dichroic mirror and then focused onto the same point inside the tissue through the
scan mirror and the objective lens. The backscattered light is collected by the same
objective lens and sent to the OCT detector. The photoacoustic wave generated from
the focused point is detected directly by the ultrasound detector.
The multimodal system can potentially provide comprehensive information
about biological tissues, including tissue anatomy, blood flow, and hemoglobin
oxygen saturation, all from a single instrument.

9.3 Development of Multimodal Imaging Systems

The fundamental requirement in developing an efficient multimodal imaging system
is that each imaging modality should have a different contrast mechanism. Oth-
erwise, the additional information gained from different imaging modalities has
limited value. The choice of modalities is driven by the contrast mechanism of
each imaging system, the tissue being studied, the depth-resolved capability, and
the working condition, such as whether the diagnosis is to be performed in vivo or
ex vivo.
Multiple imaging modalities are typically combined through spatial, spectral,
or temporal integration. In spatial integration, the imaging systems are combined
without a common component; the respective optical axes are not overlapped, but
partial or entire FOVs are overlapped. The images can be captured simultaneously