Biomedical Engineering Reference
In-Depth Information
Figures 14.21b and 14.21c. As the velocity of the RBC exceeds 0.04 mm/s, the image distortion begins to
occur due to limited frame rate (Figures 14.21d through 14.21h). The velocity of the RBC can be roughly
estimated from the lengths of the extended RBC to range from 0.05 mm/s (Figure 14.21d) to 0.1 mm/s
(Figure 14.21g), but the velocity of the RBC shown in Figure 14.21h cannot be estimated due to a much
higher velocity and serious image distortion. By using THG microscopy, the motion, shape transition,
and velocity of the RBC under flow in the dermal capillaries can be easily
in vivo
monitored. THG
microscopy can provide the potential for monitoring the velocity of RBC, determine the deformability
of RBC, diagnose the abnormal RBC (sickle shape, for example), find the abnormal aggregation of the
RBC, and so on in capillaries. Combined with SHG, which is sensitive to collagen fibers, pathological
changes of capillaries in diseases like diabetes mellitus or angiogenesis in the cancerous tissues may
possibly be easily investigated
in vivo
.
14.3.5.3 Damage evaluation
In the
in vivo
SHG/THG imaging of human skin, volunteers including 10 Caucasian skins (type I and
II), 37 Asian skins (type III and IV), and 1 African-American skin (type VI) have been investigated.
According to different appearances and tanning ability of skin, six types of skin can be distinguished fol-
lowing the Fitzpatrick skin classification (Fitzpatrick and Breathnach 1963; Fitzpatrick 1988). During the
clinical trials, the following protocols were applied: (1) the total exposure time was limited to 30 min for
each volunteer in the same area; and (2) the average excitation power was limited by 90 mW; and (3) the
frame rate was limited by 0.37 Hz. The corresponding accumulated photon energy was around 180-200 J.
Before, during, and after the SHG/THG biopsy, the tested site—ulnar, ventral, upper 1/3 forearm skin
of the volunteers were photographed and recorded. A research medical doctor continually checked and
recorded the volunteers' status during SHG/THG observations. The skin conditions of the tested area
were evaluated immediately, several hours, 24 h, 3 days, and 1 week after the experiment by a dermatolo-
gist doctor. Out of all the volunteers, only one volunteer reported a possible stingy sensation for <1 s
during observations; however, the volunteer was not certain about this claim. There were no inflamma-
tory symptoms, skin color change, pigmentation, wound, blister formation, or ulcerations reported in
the volunteers' skin. Through this damage evaluation, the noninvasiveness and safety of the SHG/THG
system can be further confirmed and according to volunteers' opinions, the procedure was comfortable.
This result thus indicates the feasibility of the SHG/THG system for
in vivo
virtual biopsy of skin.
14.3.5.4 Lateral Resolution of
In Vivo
SHG/tHG Microscopy
In the
in vivo
observation of the human skin, both the lateral resolution of THG modality at the right
skin surface and the lateral resolution of SHG modality deep in the reticular dermis have been mea-
sured. Right at the surface of the skin, the lateral resolution of THG microscopy can be analyzed from
the multilayer structure of the stratum corneum (Figure 14.22a). As shown in example Figure 14.22b,
the THG brightness is plotted versus distance along the yellow line (arrow in Figure 14.22a). The resolu-
tion is defined as the FWHM of the fitted Gaussian curves and the lateral resolution measured in this
case is 0.49 and 0.56 μm. On the other hand, since THG is too weak for measuring the lateral resolution
deep in the dermis, the lateral resolution of SHG is instead analyzed from the collagen fibers and the cor-
responding lateral resolution of THG microscopy can be obtained. Figure 14.22c shows an example of
an SHG image at 200 μm deep, the SHG brightness is plotted in Figure 14.22d) versus distance along the
yellow line (arrow in Figure 14.22c). In this case, the lateral resolution of SHG microscopy is measured
to be 0.66 μm and the corresponding lateral resolution of THG microscopy is 0.54 μm. Measuring the
resolution in the SHG and THG images of different volunteers' skin with the same protocol, the mean
lateral resolution of THG microscopy is 0.45 ± 0.05 μm right at the skin surface and 0.75 ± 0.1 μm at a
300 μm depth (Figure 14.22e). Compared with the previous image resolution analysis on fixed human
skin (Table 14.3) (Tsai et al. 2006),
in vivo
SGH/THG imaging shows a much lower resolution degrada-
tion deep in the live tissue, indicating a much reduced point-spread function aberration (Gu et al. 2000)
of the 1230 nm excitation light in the live tissues versus fixed tissues.
