Combined SHG/THG Imaging - Second Harmonic Generation Imaging - page 319

14.3 Biomedical Applications

14.3.1 imaging contrasts of SHG and tHG

In our previous ex vivo and in vivo studies, various imaging contrasts of SHG and THG microscopy
have been studied on different animal models and excised human tissues. In previous in vivo studies of
zebrafish embryos (Chu et al. 2003; Sun et al. 2004; Chen et al. 2006) (Figures 14.6a through 14.6d), SHG
was found to arise from noncentrosymmetric structures like spindle fibers (arrow in Figure 14.6a), skel-
eton muscles (arrow in Figure 14.6b), cardiac muscles (arrow in Figure 14.6c), and nerve fibers (arrow in
Figure 14.6d) in the embryos, while THG was found to arise from cell membranes (arrowhead in Figure
14.6a) and tissue inhomogeneity, and the structural changes during the embryo development can be
revealed by THG microscopy. In previous studies of mouse embryos (Hsieh et al. 2008) (Figure 14.6e),
SHG can reveal zona pellucida (arrow in Figure 14.6e) of the mouse embryos, while THG contrasts were
proved to be contributed by cytoplasmic organelles (arrowheads in Figure 14.6e). The previous studies
of mouse skin (Lee et al. 2009) (Figures 14.6f through 14.6h) show that THG contrasts are provided by
cytoplasm of keratinocytes in epidermis and the cellular morphology of epidermis (ED) can be revealed
by THG microscopy. On the other hand, in dermis (D), SHG contrasts can be found in collagen fibers

(a) (b) (c) (d)

(e) (f ) (g) (h)

ED

D

(i) (j) (k) (l)

ED

E

D

FIgurE 14.6 (See color insert.) (a)-(d) In vivo HGM images of zebrafish embryos. THG contrasts are provided by
cell membranes (arrowhead in (a)) and tissue inhomogeneity; SHG contrasts are provided by spindle fibers (arrow in
(a)), skeleton muscles (arrow in (b)), cardiac muscles (arrow in (c)), and nerve fibers (arrow in (d)). (e) In vivo HGM
image of a mouse embryo. THG contrasts are contributed by cytoplasmic organelles (arrowheads in (e)); SHG con-
trasts are contributed by zona pellucida (arrow in (e)). (f)-(g) Ex vivo and (h) in vivo HGM image of mouse skin. THG
contrasts are provided by cytoplasm of keratinocytes in epidermis (ED), and adipocytes (arrow in (g)) and red blood
cells (arrowhead in (h)) in dermis; SHG contrasts are provided by collagen fibers (arrow in (h)) in dermis (D). (i)-(l)
Ex vivo HGM images of excised human (i) teeth, (j) lung, (k) cartilage, and (l) skin. THG microscopy reveals rod
structures of the tooth enamel (i), elastic fibers in the lung tissues (arrow in (j)), chondrocytes in the cartilage (arrow
in (k)), and cellular morphology of epidermis (ED) of the skin (l); strain status of the abnormal enamel (arrow in (i)),
type II collagen in the cartilage (k) and collagenous structures of dermis (D) of the skin (l) can be revealed by SHG
microscopy. THG and SHG are represented by purple and green colors, respectively. Scale bar: 20 μm.