Biomedical Engineering Reference
In-Depth Information
8.
Given a Helium-Neon laser-based fiber optic Doppler probe at an angle of 60
o
with a blood
vessel that registers a frequency shift of 63 KHz, what is the velocity of the blood? Is this a
reasonable number from a physiologic point of view when compared to the average velocity
in the major and minor blood vessels in the human body?
9.
Assume you want to measure the thickness of a piece of tissue (
n
t
¼
1.33) bounded by air
1.0) using either the Michelson or Fabry-Perot interferometric approach. Your light
source has a wavelength of 780 nm, and your instrument can count 20 fringes. The tissue is
ablated (or cut) with a high-powered pulsed laser that removes roughly 2 micrometers of
tissue per pulse. The maximum tissue thickness before it is all removed is 20 micrometers.
(a) Calculate to see if each of the interferometer systems will have a long enough dynamic
range, without moving the system, to be used with this piece of tissue. Explain your result.
(b) Assume you want to use either of your interferometric systems as a feedback unit for the
laser removal of tissue. What is the range in the number of fringes (m
min
and m
max
) for each
of your systems in order to measure both the minimum slice thickness and the maximum
tissue thickness? Explain.
10.
In general, when is a Fabry-Perot interferometer preferred over a standard Michelson
interferometer? Can you make a Fabry-Perot interferometer that performs worse than a
Michelson interferometer? Explain.
11.
For Raman spectroscopy, what are the Stokes and anti-Stokes bands? Which bands are
typically used for sensing? What are the main challenges to overcome for Raman
spectroscopy to be used for biomedical sensing?
12.
Assume you want to measure glucose through the anterior chamber of the eye as a means of
noninvasively quantifying blood glucose. Given that glucose has a specific rotation of 41.89
degrees/(dm g/ml) at a wavelength of 656 nm, and the anterior chamber of the eye has a
path length of roughly 0.8 cm, calculate the concentration of glucose for a rotation of 15
millidegrees. Is this a reasonable value from a physiologic point of view? Would the patient
be considered normal or diabetic? Explain your result.
13.
In the near-infrared region of the optical spectrum between 600 and 1,100 nanometers, there
are well-known absorbance peaks for oxygenated and deoxygenated hemoglobin. A big
assumption can be made for the moment that in this region the dominant optical signal is
due to absorption (which is not generally the case). Given that you propagate through a
2-centimeter sample of tissue, you need to calculate three parameters: the concentration
of oxyhemoglobin, deoxyhemoglobin, and a background blood absorbance. At three
wavelengths (758 nm, 798 nm, and 898 nm), you can measure the extinction coefficients
for oxygenated (1.612, 2.072, and 2.763 mM
1
cm
1
) and deoxygenated (3.914, 2.072, and
2.072 mM
1
cm
1
) hemoglobin, respectively. The total absorption coefficients at these three
wavelengths in the tissue can be measured using a time-resolved system as 0.293 cm
1
,
0.1704 cm
1
, and 0.1903 cm
1
, respectively. Calculate the oxygenated and deoxygenated
hemoglobin levels given these parameters. Is this reasonable from a physiologic point of
view? Explain.
14.
Using the parameters of the equation for problem 7, give a graph of temperature versus time
at
(n
a
¼
z
¼
0, for
t
varying from 0 to 1 ms, using the analytical solution of the heat conduction
Continued
