Biomedical Engineering Reference
In-Depth Information
3.5
3
Ablation Temperature = 200 (C)
2.5
2
1.5
1
0.5
0
f
L
FIGURE 17.19
Effect of water content on ablation velocity.
over three times as large as its value for
1.0. The families of curves of Figure 17.18 are
more closely packed at higher values of ablation temperature. This means that the effect of a
change in
f
L
ΒΌ
f
L
on the ablation velocity is less significant at higher ablation temperatures.
17.6
FIBER OPTICS AND WAVEGUIDES IN MEDIC
INE
Rigid tubes for the examination of body cavities had already been in use for thousands of
years but in the 1800s illumination was added by means of a candle and a 45-degree mirror.
The introduction in the early 1900s of multiple lenses to transmit images led to semiflexible
tubes for insertion into the body. The use of fiber optic probes based on thin and transpar-
ent threads of glass dates back to the late 1920s but lay dormant for two decades until the
idea was revived in the 1950s. The first medical instrument, a flexible fiber optic gastro-
scope, was developed and first used on patients in 1959. In the 1960s, the first lasers were
developed, and in the early 1970s, there was a rapid development in the field of fiber optics
for communications. All of these events have contributed to the modern fiber optic probes
and endoscopes used today.
17.6.1 Principles of Fiber Optics and Waveguides
In Section 17.2.1, the interaction of light with a nonparticipating medium was
described. In that section, light was described as rays, and the Fresnel equations for the
interaction of the light rays at the boundaries of two media were derived. It was found
that, depending on the index of refraction of two slab-types of materials and the angle
of incident of the light, the amount of reflection and refraction could change. Although
transmission of light through an optical fiber is a complex problem, the phenomenon
