3. Calculate the exposure time when an x-ray control panel is set at 200 mA and
ID: 972824 • Letter: 3
Question
3. Calculate the exposure time when an x-ray control panel is set at 200 mA and 15 mA. 4. For a 50 kV anode voltage, what is the maximum photon energy of the x-ray radiation? 6. Calculate the CT number for a liver, given: Attenuation coefficient of the measured pixel = 10. Attenuation coefficient of water = 20.3. Calculate the exposure time when an x-ray control panel is set at 200 mA and 15 mA. 4. For a 50 kV anode voltage, what is the maximum photon energy of the x-ray radiation? 6. Calculate the CT number for a liver, given: Attenuation coefficient of the measured pixel = 10. Attenuation coefficient of water = 20.
3. Calculate the exposure time when an x-ray control panel is set at 200 mA and 15 mA. 4. For a 50 kV anode voltage, what is the maximum photon energy of the x-ray radiation? 6. Calculate the CT number for a liver, given: Attenuation coefficient of the measured pixel = 10. Attenuation coefficient of water = 20.
Explanation / Answer
The exposure time on an X-Ray machine depends on the density
One of the photographic properties that determines visibility of detail
Various anatomical parts have different density
If the density in mAs is 25 which needs to be evaluated then
mAs = mA x time(s)
25 mAs = 200 mA x time (s)
time (s) = 0.125 s
similarly
25 mAs = 15 mA x time (s)
time (s) = 1.67 s
4)
The maximum photon energy is
hf=qV
where q is the charge of the electron and V is the accelerating voltage. Thus,
hf=(1.60×10–19C)(50.0×103V)
From the definition of the electron volt, we know 1 eV=1.60×10–19J, where 1 J=1 CV.
converting energy to eV yields
hf=(50.0×103)(1.60×10–19CV)(1 eV/1.60×10–19CV)=(50.0×103)(1 eV) = 50.0 keV
6)CT number = 1000 x (uvoxel - uwater)/uwater
CT number = 1000 x 10-20/20
CT number = 1000 x -10/20
CT number = -500
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