SEMMELWEIS UNIVERSITY, MEDICAL
BIOPHYSICS - FINAL EXAM
QUESTIONS & CORRECT ANSWERS
Coulter principle. - correct answer ✔✔The ability to count and measure the size of particles
using an electric circuit. Particles are moved through a small aperture, their presence causes a
narrowing of the aperture, which leads to an increase in resistance. By using constant I,
According to Ohms law (U= I * R), when R increases, U increases and pulse is generated.
Parts and functions of the Coulter-counter - correct answer ✔✔- Two spaces with a small
aperture in between, capillary (contains the electrolyte solution with the cells)
- Measuring electrode, one in each of the spaces (closing the circuit and measuring voltage
between the two spaces)
- Pump (draws the solution into the smaller space, and out
again, through the capillary)
- Auxiliary electrode (signals when certain volume is
reached, to initiate pumping out of the solution)
- Integral Discriminator (filter out noise)
- Differential Discriminator (mapped of the size distribution
of the particles)
How does the voltage pulse amplitude depend on particle size in the Coulter-counter? - correct
answer ✔✔Its proportional, bigger particle will form higher resistance, higher voltage pulse.
How do you separate the red-blood-cell versus white-blood-cell signals in a Coulter-counter? -
correct answer ✔✔when you want to measure RBC, it's not necessary to separate them from
the RBC b.c. the number of WBC is negligible (less than error of the measurement)
,By hemolyze RBC and measured them separately photochemically and subtracted the result
from the coulter-counting measurement
How do you separate the red-blood-cell versus platelet signals in a Coulter-counter? - correct
answer ✔✔By integral discrimination (the size of the platelets is much
smaller)
What is the role of differential discriminator in Coulter-counting? - correct answer ✔✔Mapping
the size distribution of the particle
Why is dilution of blood is necessary in Coulter-counting? - correct answer ✔✔Because the cells
themselves do not conduct well, and so we dilute them with an electrolyte solution so changes
in resistivity are noticed. Also, for practical reasons (e.g. we don't want the solution to dry up.)
What solution is used for blood dilution in Coulter-counting? - correct answer ✔✔Saline
solution, for optimal osmotic pressure (keep the RBCs in their natural size) and for good
conduction (NaCl)
How does the matter flow density (flux) change if the concentration gradient is doubled? -
correct answer ✔✔It doubles, due to flicks first law: Jv=-Dxdeltac/deltax
Name the parameters influencing the value of diffusion coefficient. - correct answer ✔✔Size
and shape of the particle as well as the temperature and viscosity of the medium. Can be
calculated for spherical particles: D=kT/6 pi n r
What diffuses faster: a potassium ion or a virus particle? - correct answer ✔✔K+ ion due to
smaller diffusion coefficient (smaller size)
,How does the average distance travelled by a diffusing particle depend on time? - correct
answer ✔✔Square root function (Distance average ^2 =6 * D * t)
On what length scale is diffusion an effective transport process? - correct answer ✔✔On a small
scale
How does the minimum wavelength of the x-ray spectrum change with increasing anode
voltage? - correct answer ✔✔Decreases (higher voltage higher kinetic energy higher frequency
spectrum) - Duane-hunt law
How does the minimum wavelength of the x-ray spectrum change with increasing anode
current? - correct answer ✔✔Does not change
What is the maximum x-ray photon energy at 50 kV anode voltage? - correct answer ✔✔50 keV
What elements are suitable as x-ray-tube anode material? - correct answer ✔✔High melting
point and high atomic number materials molybdenum
(more common in medical diagnosis) and tungsten.
What are the x-ray spectral lines characteristic of? - correct answer ✔✔Anode material
Why do we need to cool the x-ray-tube anode? - correct answer ✔✔Because it heats up due to
low efficiency in the conversion of high
kinetic energy to x-ray.
How does x-ray absorbance depend on the atomic number of
absorber? - correct answer ✔✔Photo Effect is the dominant attenuation process: photoeffect =
micro m - Z^3
, Which part of the x-ray spectrum is attenuated by filtering? - correct answer ✔✔The long
wavelengths (to avoid unnecessary radiation absorption, these photons and may hurt resolution
due to scattering)
Which is a better x-ray absorber: Al or Ag? - correct answer ✔✔Element with the higher atomic
number: Ag
Which attenuation mechanism dominates in x-ray diagnostics? - correct answer ✔✔Photoeffect
What are the parts of a gamma-radiation pulse amplitude spectrum. - correct answer ✔✔Noise,
Compton region and photo-peak.
Effect of activity on the pulse amplitude spectrum of a gamma- radiating isotope. - correct
answer ✔✔Increase the value of the pulse rate (y axis)
Effect of anode voltage on the pulse amplitude spectrum of a gamma-radiating isotope. -
correct answer ✔✔The pulse-amplitude spectrum shifts to the right to higher values (x axis)
Compare the pulse amplitude spectra of two different gamma- radiating isotopes. - correct
answer ✔✔
How can you determine the gamma energy of a radioactive isotope with a scintillation counter?
- correct answer ✔✔The location of the photo-peak on the x-axis indicates the energy of the
gamma photon. The voltage of the photo-peak is proportional to the energy of the gamma
radiation. Because during the photo-effect all the energy of the photon is converted to the
primary electron.
What type of discriminator is used for acquiring the pulse amplitude spectrum? - correct answer
✔✔Differential discriminator (allows us to differentiate the pulse rate
values): which allows us to find the photo-peak
BIOPHYSICS - FINAL EXAM
QUESTIONS & CORRECT ANSWERS
Coulter principle. - correct answer ✔✔The ability to count and measure the size of particles
using an electric circuit. Particles are moved through a small aperture, their presence causes a
narrowing of the aperture, which leads to an increase in resistance. By using constant I,
According to Ohms law (U= I * R), when R increases, U increases and pulse is generated.
Parts and functions of the Coulter-counter - correct answer ✔✔- Two spaces with a small
aperture in between, capillary (contains the electrolyte solution with the cells)
- Measuring electrode, one in each of the spaces (closing the circuit and measuring voltage
between the two spaces)
- Pump (draws the solution into the smaller space, and out
again, through the capillary)
- Auxiliary electrode (signals when certain volume is
reached, to initiate pumping out of the solution)
- Integral Discriminator (filter out noise)
- Differential Discriminator (mapped of the size distribution
of the particles)
How does the voltage pulse amplitude depend on particle size in the Coulter-counter? - correct
answer ✔✔Its proportional, bigger particle will form higher resistance, higher voltage pulse.
How do you separate the red-blood-cell versus white-blood-cell signals in a Coulter-counter? -
correct answer ✔✔when you want to measure RBC, it's not necessary to separate them from
the RBC b.c. the number of WBC is negligible (less than error of the measurement)
,By hemolyze RBC and measured them separately photochemically and subtracted the result
from the coulter-counting measurement
How do you separate the red-blood-cell versus platelet signals in a Coulter-counter? - correct
answer ✔✔By integral discrimination (the size of the platelets is much
smaller)
What is the role of differential discriminator in Coulter-counting? - correct answer ✔✔Mapping
the size distribution of the particle
Why is dilution of blood is necessary in Coulter-counting? - correct answer ✔✔Because the cells
themselves do not conduct well, and so we dilute them with an electrolyte solution so changes
in resistivity are noticed. Also, for practical reasons (e.g. we don't want the solution to dry up.)
What solution is used for blood dilution in Coulter-counting? - correct answer ✔✔Saline
solution, for optimal osmotic pressure (keep the RBCs in their natural size) and for good
conduction (NaCl)
How does the matter flow density (flux) change if the concentration gradient is doubled? -
correct answer ✔✔It doubles, due to flicks first law: Jv=-Dxdeltac/deltax
Name the parameters influencing the value of diffusion coefficient. - correct answer ✔✔Size
and shape of the particle as well as the temperature and viscosity of the medium. Can be
calculated for spherical particles: D=kT/6 pi n r
What diffuses faster: a potassium ion or a virus particle? - correct answer ✔✔K+ ion due to
smaller diffusion coefficient (smaller size)
,How does the average distance travelled by a diffusing particle depend on time? - correct
answer ✔✔Square root function (Distance average ^2 =6 * D * t)
On what length scale is diffusion an effective transport process? - correct answer ✔✔On a small
scale
How does the minimum wavelength of the x-ray spectrum change with increasing anode
voltage? - correct answer ✔✔Decreases (higher voltage higher kinetic energy higher frequency
spectrum) - Duane-hunt law
How does the minimum wavelength of the x-ray spectrum change with increasing anode
current? - correct answer ✔✔Does not change
What is the maximum x-ray photon energy at 50 kV anode voltage? - correct answer ✔✔50 keV
What elements are suitable as x-ray-tube anode material? - correct answer ✔✔High melting
point and high atomic number materials molybdenum
(more common in medical diagnosis) and tungsten.
What are the x-ray spectral lines characteristic of? - correct answer ✔✔Anode material
Why do we need to cool the x-ray-tube anode? - correct answer ✔✔Because it heats up due to
low efficiency in the conversion of high
kinetic energy to x-ray.
How does x-ray absorbance depend on the atomic number of
absorber? - correct answer ✔✔Photo Effect is the dominant attenuation process: photoeffect =
micro m - Z^3
, Which part of the x-ray spectrum is attenuated by filtering? - correct answer ✔✔The long
wavelengths (to avoid unnecessary radiation absorption, these photons and may hurt resolution
due to scattering)
Which is a better x-ray absorber: Al or Ag? - correct answer ✔✔Element with the higher atomic
number: Ag
Which attenuation mechanism dominates in x-ray diagnostics? - correct answer ✔✔Photoeffect
What are the parts of a gamma-radiation pulse amplitude spectrum. - correct answer ✔✔Noise,
Compton region and photo-peak.
Effect of activity on the pulse amplitude spectrum of a gamma- radiating isotope. - correct
answer ✔✔Increase the value of the pulse rate (y axis)
Effect of anode voltage on the pulse amplitude spectrum of a gamma-radiating isotope. -
correct answer ✔✔The pulse-amplitude spectrum shifts to the right to higher values (x axis)
Compare the pulse amplitude spectra of two different gamma- radiating isotopes. - correct
answer ✔✔
How can you determine the gamma energy of a radioactive isotope with a scintillation counter?
- correct answer ✔✔The location of the photo-peak on the x-axis indicates the energy of the
gamma photon. The voltage of the photo-peak is proportional to the energy of the gamma
radiation. Because during the photo-effect all the energy of the photon is converted to the
primary electron.
What type of discriminator is used for acquiring the pulse amplitude spectrum? - correct answer
✔✔Differential discriminator (allows us to differentiate the pulse rate
values): which allows us to find the photo-peak
