Semmelweis University, Medical Biophysics - Final Exam Questions With 100 % Correct Answers | Verified

Coulter principle. - 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 - 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? - 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? - 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? - Answer-By integral discrimination (the size of the platelets is much smaller)What is the role of differential discriminator in Coulter-counting? - Answer-Mapping the size distribution of the particle Why is dilution of blood is necessary in Coulter-counting? - 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? - 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? - Answer-It doubles, due to flicks first law: Jv=-Dxdeltac/deltax Name the parameters influencing the value of diffusion coefficient. - 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? - Answer-K+ ion due to smaller diffusion coefficient (smaller size) How does the average distance travelled by a diffusing particle depend on time? - Answer-Square root function (Distance average ^2 =6 * D * t) On what length scale is diffusion an effective transport process? - Answer-On a small scale How does the minimum wavelength of the x-ray spectrum change with increasing anode voltage? - 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? - Answer-Does not change What is the maximum x-ray photon energy at 50 kV anode voltage? - Answer-50 keV What elements are suitable as x-ray-tube anode material? - 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? - Answer-Anode material Why do we need to cool the x-ray-tube anode? - 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? - Answer-Photo Effect is the dominant attenuation process: photoeffect = micro m - Z^3 Which part of the x-ray spectrum is attenuated by filtering? - 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? - Answer-Element with the higher atomic number: Ag Which attenuation mechanism dominates in x-ray diagnostics? - Answer-Photoeffect What are the parts of a gamma-radiation pulse amplitude spectrum. - Answer-Noise, Compton region and photo-peak. Effect of activity on the pulse amplitude spectrum of a gamma- radiating isotope. - Answer-Increase the value of the pulse rate (y axis) Effect of anode voltage on the pulse amplitude spectrum of a gamma-radiating isotope. - 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. - AnswerHow can you determine the gamma energy of a radioactive isotope with a scintillation counter? - 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? - Answer-Differential discriminator (allows us to differentiate the pulse rate values): which allows us to find the photo-peak Define the human hearing range (thereshold of hearing, threshold of pain, frequency limits). - Answer-Threshold of hearing is the minimum intensity at various frequencies that a human can hear. The threshold for pain is the highest intensity that a human can hear for a short time without damage to the ear (10 W/m^2). The frequency range is between 20Hz-20kHz. Which one is louder: 50 Hz, 120 dB vs. 1 kHz, 110 dB (formula collection, isophone curves) - AnswerThey have the same loudness value Which one is louder: 30 Hz, 90 dB vs. 1 kHz, 70 phon (formula collection, isophone curves) - Answer- 1kHz at 70 phon How much louder is a 80 dB versus a 70 dB sound at 1000 Hz? - Answer-Twice as loud