Biomedical Engineering Reference
In-Depth Information
Fig. 2.8 Schematic of the
hybrid-scanning
optical-resolution
photoacoustic microscopy
system
material PZT, GE). The transducer has a line focus and thus frees acoustic scanning
in the B-scan direction. The entire imaging head is mechanically scanned by a 1-D
translation stage to form a volumetric image. The HSOR-PAM system operates at
an imaging speed of 5,000 A-lines/s, with a slightly degraded SNR (5 dB lower)
compared with traditional OR-PAM.
2.8.2
Integration with Optical Coherence Tomography
Recently, Li et al. reported the first combined system integrating transmission-
mode OR-PAM with spectral-domain OCT [ 28 ]. In this combined system (Fig. 2.9 ),
OR-PAM and OCT share the same single-mode fiber (P1-630A-FC-2, Thorlabs) for
light delivery and the same microscope objective (E1, Leica) for optical illumina-
tion. Two-dimensional mechanical scanning of the object platform, in combination
with the depth-resolved optical/ultrasonic detection, provides volumetric OCT/OR-
PA M i m a g e s .
Although the present imaging system demonstrates the feasibility of integrating
OR-PAM with OCT, the relatively slow mechanical scanning limits its practical
values. Taking advantage of the recently developed LSOR-PAM technology, Jiao
et al. developed a combined laser-scanning-based OR-PAM and OCT system [ 29 ].
Figure 2.10 shows a schematic of the combined system. The configuration of the
LSOR-PAM subsystem is the same as the one shown in Fig. 2.7 . To incorporate
the OCT subsystem, a dichroic mirror (NT43-955, Edmund Optics) is inserted right
before the 2-D galvanometer (QS-10, Nutfield Technology). The passband of the
dichroic mirror is carefully chosen to ensure a perfect reflection of the OCT beam
and a maximized transmission of the OR-PAM beam. Then, the combined OCT and
OR-PAM beams are focused into the object by an achromatic lens (AC254-060-A1,
Thorlabs) and optically scanned by the galvanometer to form co-registered OCT and
OR-PAM images.
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