Diagnostic Imaging - Generation of X-rays Flashcards
What is radiation?
Electromagnetic energy travels through space in electrical & magnetic waves
What are properties of X-rays?
- have very short wavelength & are high energy
- cause ionization
- travel in straight lines
- can cause biological damage to tissue
How does an x-ray tube work?
photons are produced by applying a charge across the x-ray tube head which contains a negative electrode, the cathode & a positive electrode (the anode)
X-ray tubes are lead-lined on the…
outside
Tungsten in the x-ray tube is used for…
both the filament of the cathode and the focal spot of the anode because it has a high melting point
Applying a small current to the x-ray tube gives enough energy to…
free some elctrons from the cathode-thermionic emission
the focusing cup of an x-ray tube is kept more…
negatively charged to keep the freed electrons together in an electron cloud
Applying a potential difference between the cathode and the anode occurs when
kilovoltage attracts the free electrons to the anode where they interact with the focal spot to produce xrays
increase in KV causes
an increase in the number & penetrating power of x-rays
increase mA causes
increase in the number of x-ray photons produced but not the penetrating power
overheating in the x-ray tube is a major problem of
the filament and the focal spot
How can over-heating be prevented in the x-ray tube?
- use a broad focus for the cathode
- use effective focal spot as larger than actual focal spot to spread out the heat generated
- use tungsten target in the anode
- use copper and colling fins with oil
- use rotating anode
- minimise exposure settings and repeat rads
Broad focus should be used for
higher exposure
fine focus should be used for
smaller exposures for better detail
Rotating anodes rotates…
so that electrons hit a different part of the focal spot
Aside from the x-ray tube, an x-ray machine is composed of…
light beam diaphragm
control panel
The control panel controls…
KV
mAs-mA and time settings
Exposure button
exposure factors are expressed in terms of
KV & mAs
With the exposure switch, what does the first position on the 2-step switch do?
- prepares the x-ray tube
- heats the filament
- rotates the anode
With the exposure switch, what does the second position on the 2-step switch do?
- produces the x-rays (exposure)
What are the types of x-ray machines available?
portable, high-frequency portable, mobile, fixed
x-ray photons can penetrate tissue and…
some photons will pass through unchanged
some will be attenuated by the tissue
What is attenuation?
the reduction of the intensity of the primary x-ray beam as it passes through matter
Attenuation =
photoelectric absorption + Compton scatter
