X-radiation and MRI Flashcards
(25 cards)
What is the process of X-ray generation in the X-ray tube?
Electrons are emitted from the cathode by thermionic emission and are accelerated towards a high voltage anode, producing X-rays and heat through Bremsstrahlung and other interactions.
What is the formula for energy of an incident electron in an X-ray tube?
E = V × e, where V = tube voltage and e = charge of an electron.
What is the inverse square law for radiation?
Intensity ∝ 1/distance², meaning intensity is inversely proportional to the square of the distance from the source.
How is the intensity of X-rays through absorbing material calculated?
I = I₀ e^(-µx), where I₀ = initial intensity, µ = linear attenuation coefficient, x = distance through material.
What is the half value thickness of a material?
X₁/₂ = log(e) 2 / µ, which is the thickness that halves the original intensity of the beam.
What is the mass attenuation coefficient formula?
µₘ = µ / density, where µₘ is the mass attenuation coefficient.
What are the primary medical applications of X-rays?
X-rays are used for imaging bones, detecting fractures, and targeting cancer cells in radiation therapy.
How does an intensifying screen work in X-ray imaging?
The screen absorbs X-ray energy and re-emits it as light through fluorescence, reducing exposure time.
What is a barium meal and why is it used in X-ray imaging?
A barium meal is ingested to line the intestines with a radiopaque substance, increasing contrast in X-ray imaging.
What is Computed Tomography (CT scanning)?
CT scanning uses rotating X-ray beams to build a 3D image from 2D slices, enhancing diagnostic imaging.
What is the effect of ionising radiation from X-rays?
Ionising radiation can damage cells, potentially causing cancer or sterility with prolonged exposure.
What is the basic principle of MRI?
MRI uses the precession of atomic nuclei in a magnetic field, detected as RF radiation, to generate images of tissues.
What is Lamor frequency in MRI?
Lamor frequency is the frequency of precession of nuclear spins in a magnetic field, determined by the magnetic field strength.
How are high coil temperatures managed in MRI machines?
By using copper coils with cooling water to dissipate heat during electromagnetic pulses.
What are the key magnetic circuit terminologies in MRI?
Magnetic flux, flux density, magnetomotive force, magnetising force, permeability, reluctance, leakage, and fringing.
A 79kV X-ray tube operates with a current of 105mA. If 1∙5% of the supplied power is converted to X-rays determine the X-ray intensity at a distance of 2m from the tube
(2∙47Wm-2)
A parallel beam of X-rays of total power 2mW and c-s-a 50mm2 is incident on 4∙5mm thick copper sheet. If the ½ value thickness for copper for the particular energy distribution of the beam is 1∙5mm, calculate the intensity of the X-rays that emerge from the other side of the sheet.
(5Wm-2)
A filtered and collimated beam of X-rays with an intensity of 200W.m-2 is incident on a metal foil of thickness 0.06mm. If the intensity of the emergent beam is 187W.m-2 and the density of the metal is 10280 kg.m-3, determine the mass attenuation coefficient and the half value thickness of the metal.
(0∙11m2kg-1, 0∙618.10-3m)
What are the meanings for the following symbols:
Number of turns
Length of magnetic circuit
Magnetic flux
Magnetic flux density
Magnetomotive force
Magnetising force
Permeability
Permeability of air = 4π.10-7
Relative permeability
Reluctance
What is the difference between magnetic and electrical (4)
Draw a diagram of an iron cored coil and an air cored coil in terms of magnetising force and magnetic flux density
The intensity of radiation at a distance of 2m from a point source is 300mWm-2. Determine the intensity at 6m from the source.
(33∙3mWm-2)
A parallel beam of X-rays is incident on 6mm thick copper sheet. If the ½ value thickness for copper for the particular energy distribution of the beam is 1∙5mm, calculate the incident intensity if the X-rays that emerge from the other side of the sheet have an intensity of 4W/m2.
(64 W/m2)
A filtered and collimated beam of X-rays with an intensity of 250W.m-2 is incident on a metal foil of thickness 0.08mm. If the intensity of the emergent beam is 230W.m-2 and the density of the metal is 10280 kg.m-3, determine the mass attenuation coefficient and the half value thickness of the metal.
(0∙1m2kg-1, 0∙665.10-3m)
