Biomedical Engineering Reference
In-Depth Information
17.8 EXERCISES
1. (a) Name at least three reasons why it might be desirable to use optic or fiber optic sensors for
biomedical applications. (b) Name three potential drawbacks to using optic or fiber optic
biomedical sensors.
2. In one paragraph, or using bullets, explain the similarities and differences among polarization,
luminescence, absorption, scatter, and Raman scattering of light.
3. Given an interface between clear tissue (i.e., water;
1.5), compute the
transmission angle for a beam incident in the water at 45 o . If the transmitted beam is reversed
so it impinges on the interface from the glass side, calculate what the transmitted angle will
be through the tissue. Does this make sense? Explain.
4. Using MATLAB, or some other software, plot (
n t ¼
1.33) and glass (
n g ¼
2 ) and (
2 ) as a function of the
R ? ¼ r ?
R p ¼ r p
1.0) interface. Explain what it means.
5. An Nd:YAG laser operating at 1,064 nm with a Gaussian beam is to be used for performing a
port-wine stain treatment. Assume a heuristic model for light distribution in a homogeneous
material such that
input angle
y i for a glass (n i ¼
1.5) and air (n t ¼
o b ) 2 ), where
m 0 s being the
absorption and reduced scattering coefficients. For the following multilayer case at r
m ¼ m a þ m 0 s ,
I
(
r,z
)
¼
I o exp(-
m z
) exp(-2(
r
/
m a and
0, give
the expressions and graph intensity I and the rate of heat generation Q in the tissue by the
laser,
¼
1. The absorption and scattering coefficients of
each skin layer and blood vessel for this wavelength are given below. Discuss how selective
photothermolysis of the blood layer is achieved.
(
r ¼
0,
) and
(
r ¼
0,
). Assume
I o ¼
I
z
Q
z
r
μ a (cm 1 )
(cm 1 )
μ s
epidermis
65 μ m
Blood
20
20
dermis
z
300
μ
m
Epidermis
0.1
10
blood vessel
dia = 80 μ m
Dermis
0.5
10
0.1 cm 1 . Using
the diffusion approximation, graph on the same plane the logarithm of relative intensity
versus radius for four different values of reduced scattering coefficient—
6. Consider a turbid biological tissue with an absorption coefficient of
m a ¼
m 0 s ¼
1, 10, 50,
and 100 cm 1
varying from 0.1 cm to 2 cm. Describe the results in terms of the effect of
scattering on the intensity profile.
7. For liver tissue irradiated by the pulsed Ho:YAG laser, determine the exposure duration
during which the equation for heat conduction may be ignored. Assume that the absorption
coefficient at the Ho:YAG laser wavelength is 30 cm 1 , and assume the thermal diffusivity of
the tissue is the same as that of water. If the threshold temperature of ablation is 150 o C,
determine the threshold fluence ( J/cm 2 ) for ablation.
r
Search WWH ::




Custom Search