Combined SHG/THG Imaging - Second Harmonic Generation Imaging - page 340

modality with the THG contrast arising from hemoglobin (Tai et al. 2007), and both the movement and
deformation of the RBC can be dynamically recorded. In the previous THG study (Yu et al. 2007), elas-
tic fibers were revealed by THG modality in the human lung tissues and the THG contrast of the elastic
fibers has been proven through H&E staining. In the in vivo SHG/THG images of the dermis, the THG-
revealed elastic fibers and SHG-revealed collagen fibers are found to interlace (Figures 14.20d-1 through
14.20d-5), while in the separated THG images, the elastic fibers can be identified more clearly (arrows
in Figures 14.20e-1 through 14.20e-5). Compared with the reflection confocal microscopic imaging of
dermis, the cellular information and elastic fibers are all more distinguishable from the collagen fibers
in the SHG/THG biopsy. This is due to a much improved spatial resolution and through the assistance
of the simultaneous SHG contrast of collagen fibers.
14.3.5.2 Dynamic information Recorded by In Vivo SHG/tHG imaging
In contrast to ex vivo SHG/THG imaging, similar static morphological information and imaging con-
trasts can be obtained from in vivo SHG/THG imaging, while valuable dynamic skin information like
blood flow can only be recorded through in vivo SHG/THG imaging. Based on the THG contrast pro-
vided by hemoglobin, the RBC in the capillary can be clearly observed, and the movement, aggrega-
tion, and deformation of the RBC in the same capillary with a diameter of 12.6 μm are recorded at
different seconds, as shown in Figures 14.21a through 14.21h. According to previous reports (Noguchi
and Gompper 2005), human RBC have a biconcave-disk shape with a diameter of 8 μm and are easily
deformed from a nonaxisymmetric discocyte to an axisymmetric parachute shape (coaxial with the
flow axis) (Boryczko et al. 2003; Noguchi and Gompper 2005) to reduce the flow resistance of blood in
capillaries. A reduction of RBC deformability and an enhanced flow resistance of blood can be found in
some diseases, such as diabetes mellitus and sickle cell anemia (Tsukada et al. 2001; Havell et al. 2006).
In Figures 14.21a through 14.21c, the RBC moving at a velocity lower than 0.04 mm/s are shown with
a diameter of 7.5 μm, as expected from histological results, and the aggregation of the RBC, which is
often seen in the capillaries, can be observed in Figure 14.21c. In Figure 14.21a, the RBC are shown
in a biconcave-disk shape, while the axisymmetric parachute shape of the RBC can be observed in
FIgurE 14.21 In vivo HGM images of blood flow in a capillary, dynamically recorded at different seconds. The
red blood cells were found to appear in a (a) biconcave-disk shape or in a (b) axisymmetric parachute shape. (a)-(c)
Red blood cells moved at a velocity lower than 0.04 mm/s and aggregation of the red blood cells can be observed in
(c). (d)-(h) When moving faster, the imaged red blood cells began to be distorted due to limited frame rate. Scale
bar: 20 μm.