Biomedical Engineering Reference
In-Depth Information
fibers can still be revealed through THG. Since the total thickness of the human cornea is about 535 μm
(Jalbert et al. 2003), a penetration depth greater than 700 μm indicates the ability to investigate even the
deepest part of the human cornea. With different imaging capabilities of SHG and THG modalities, not
only the collagenous structures of the CS but also the cellular morphology of the EP and ED, and the
structures of the lens fibers can be resolved with high resolution, and the combined SHG/THG micros-
copy is a suitable tool for cornea diagnoses.
14.3.4 Human tissues
From the SHG/THG results of animal models, the imaging capabilities of SHG and THG modalities are
demonstrated and SHG/THG microscopy is shown to be a potential tool for diagnoses of various dis-
eases. With the strong SHG contrasts in the collagen fibers, SHG modality is able to reveal the changes
of the collagenous structures of various human connective tissues like the dermis of skin (Chen et al.
2009a, 2010; Cicchi et al. 2010), the submucosa of oral cavity (Tsai et al. 2010a), cardiac muscles (Tsai
et al. 2010b), the cartilage (Tsai et al. 2009), and the bone (Tsai et al. 2009) in human bodies. Based on
these SHG-revealed changes, SHG modality can be applied to diagnoses of significant diseases with
pathological changes of collagenous structures involved, for example, skin cancers. On the other hand,
the SHG contrasts are also found to arise from the strains in the tooth enamel (Chen et al. 2008) and
these imaging contrasts can help to reflect the changes of the enamel rods due to white spot lesions, ther-
mal damages, and physical cracks, and has potentials for enamel diagnoses. By combining SHG with
THG, more morphological, cellular, and molecular information can be provided by THG modality. The
valuable THG-revealed information is useful for recognizing and localizing the observed SHG signals
and helps to increase the diagnosis accuracy. In the following subsection,
ex vivo
SHG/THG imaging
of human skin, including normal human skin and various diseased human skin, is demonstrated to
show the capability of SHG/THG microscopy for skin disease diagnosis (Chen et al. 2010). For further
clinical applications, the SHG/THG microscope with backward-collection geometry was used for these
preliminary studies.
14.3.4.1 normal Human Skin
As observed in the mouse skin, SHG microscopy can also show the collagenous structures of the dermis
of human skin, while THG microscopy can provide more cellular and morphological information of
both the dermis and epidermis of human skin. Figure 14.15 shows a series of SHG/THG images obtained
at the epidermis (Figures 14.15a through 14.15c), the dermo-epidermal junction (Figure 14.15d), and
the dermis (Figures 14.15e through 14.15h) of an excised normal human skin. Similarly, the dermis
of the human skin can also be divided into two layers—the papillary dermis and reticular dermis. In
the papillary dermis (Figures 14.15d and 14.15e), the collagen fibers are shown to be loose and areolar,
while the collagen fibers in the thick reticular dermis are found to be dense and irregular (Figures 14.15f
through 14.15h). Although the different collagenous structures in the papillary and reticular dermis
can be clearly distinguished through the SHG images, the important cellular information in the dermis
still lacks. Combining SHG with THG modality, the intradermal cellular information, including the
inactivate melanocytes (arrow in Figure 14.15d) and the fibroblasts (arrowheads), can be revealed based
on the THG contrasts arising from the optical inhomogeneity and cytoplasmic organelles. In addition,
the RBC in the dermal capillaries are able to be shown by THG based on resonantly enhanced THG
contrast with oxyhemoglobin (Clay et al. 2006; Tai et al. 2007; Chang et al. 2010). However, owing to
the loss of the blood during excision, no RBC can be observed in the excised human skin specimen. By
applying THG modality for human skin imaging, more than the dermis, the cellular morphology of the
epidermis can also be revealed to reflect lots of diagnostic information about cell disorders in the epider-
mis. The epidermis of the human skin can be divided into four layers—the stratum corneum, stratum
granulosum, stratum spinosum, and the stratum basale. At the skin surface of the normal human skin,
the dead and cornified stratum corneum (arrow in Figure 14.15a) produces strong THG contrast caused
