Radiation and X-ray equipment Flashcards
Bremsstrahlung is the most prevalent mechanism of?
X-ray production (85% at 100kVp)
Bremsstrahlun gdoes NOT involve an electron striking another particle in the target- it involves…
interaction between the incident electron and the nucleus of a target atom
“braking radiation” means?
it gets bent around the curve of the nucleus, deflected by the
magnetic pull of the nucleus.
The closer to the nucleus an electron goes, the more severely its course is?
changed and the greater the energy released as it “brakes around the corner”
Bremsstrahlung radiation represents a spectrum of
wavelengths (varying degrees of “braking” thus varying energies of resultant photons)
Characteristic radiation represents only 15% of?
the origin of the Xray beam @ 100kVp
o Characteristic radiation prevalence increases…
when you raise kVp higher
Characteristic radiation is caused by?
ejection of an inner shell electron by collision between the incoming and the native electron
This radiation has a specific wavelength because?
it happens when an L shell electron drops into the K shell when the K shell electron was knocked out in the collision.
The change in energy from L shell to K shell is?
predictable and constant
X-ray beam types:
o Primary radiation
o Secondary/scatter radiation
o Remnant radiation
Primary radiation
- from the tube to the patient
Secondary/scatter radiation
- created by the beam’s interaction with the patient and almost always has LESS energy than primary radiation
Remnant radiation
- radiation that goes through the patient and creates the image we will see
Anode charge
positive
Anode has what kind of target?
tungsten
Are x rays formed on the anode side?
yes
Anodes focal spots
small focal spot is a central region within the larger focal spot
Anodes have what kind of housing?
copper for target (heat management)
Anodes rotor is?
motorized (hence the extra wire going into the anode side of the tube housing)
rotating anode is for?
r heat management and increased durability of the anode
Cathode have what kind of charge?
negative
How many filaments does a cathode have?
2: small and large
Cathode focusing cup used to?
focus electrons towards a point (instead of allowing them to
diverge from the filament)
thermionic emission creates?
the space charge (electron cloud)
mA and time determines the # of?
electrons
Glass is Pyrex, housing is metal and there is oil within- all designed to manage?
heat and contain radiation produced that will not be useful beam
Leakage radiation is?
X-rays that escape the tube housing
Actual focal spot vs. effective focal spot is a function of?
anode angle and whether you are using large or small focal spot
Anode angle is usually in the range of?
10-20 degree range; 12 degrees usually
12 degrees reflects a balancing act:
keeping the actual focal spot as large as possible (heat dissipation)
keeping the effective focal spot size as small as possible (detail and
image sharpness)
minimizing “heel effect” (lower anode angles = larger heel effect)
Anode angle is calculated from?
from the vertical axis to the face of the anode
larger angle = larger effective focal spot
The anode side of the beam will be less or more intense than the cathode side of the beam?
less
mAs:
rate of flow of electrons- determines quantity of X-ray photons in the beam
radiation exposure is a function of mA and time (s)
film density varies proportionately (linear relationship, or “directly”) with mAs
kVp:
- controls speed of electrons to the target from the cathode, hence responsible for the energy (wavelength) of photons and the resultant X-ray beam
- penetration ability of the beam is a function of kVp
- the radiographic scale of contrast is a function of kVp
Electricity
we use fully rectified 60 cycle/second electricity resulting in 120 “pulses” of
electricity per second.
