Basics Flashcards
What is the wavelength of Xrays?
0.01 to 10 nm
Hard X rays 0.1-0.2 nm–> Higher Energy and used in medical imaging
What eV does a photon need to be ionizing?
15 eV
Where do Gamma Rays originate?
Nuclei of an Atom
What does the binding force inversely proprotional to?
Square of the distance between the nucleus and the electron shell
What is the K Shell Binding Energy of Tungstun?
-69.5 kEV
Why do you add rhenium to the Tunsten filament?
To prevent cracking from multiple cycles of healing and cooling
What is Thermionic emission?
Heat the filament–> Kinetic energy–> Electrons “boil off”
Why is there a glass tube around the anode and cathode?
To create a vacuum which allows you to control the speed and amount of electrons
What is the space charge effect?
At the filament (Cathode, neg charge), which the elctrons boil off, a space cloud forms around the filament (neg), but as they boil off the cathode starts to have a slightly positive charge that pulls in the cloud. Once equilibrium is reached, additional boiled electrons will result in another electron leaving the cloud.
What is a focusing cup?
Metallic cup places around filament to help the electrons hit the anode at an acceptable size.
Actual focal spot versus effective focal spot
Actual is where the electrons hit the anodes. Effective is where it hits the patient
How do you dissapate heat at the anode?
- Rotating Anode
2. Angle the Anode
How does the Anode angle affect focal spot?
Smaller (steeper) angle= Smaller focal spot but more heel effect
What makes the heel effect worse?
- Smaller Anode Angle
- Small focus to film distance
- Large Field of View
How can you make the heel effect better?
- Larger Anode Angle
- Larger Focus to film distance
- Small Field of view
What is the difference between keV and kVp
kVp= the PEAK kilovoltage keV= The kilovoltage of one electron
What is Brehmstalung?
Braking Radiation that creates a continunum of x ray energies based on how close to the nucleus it deviates.
What determines the highest and lowest energy and the bremstrahlung curve?
Higher= Max kVP Lowest= Depends on the Filter used
What is the amount Brehmstrahlung interactions proportional to?
- Incoming energy of the charged particle
2. Atomic Number (higher= better)
What is beam intensity?
Number of X rays multipled by energy (R/min)
Intensity is proportional to kVp squared
How does changing Target Material effect Brehmstrahlung and Characteristic Radiation?
- Higher Z= more Brehmstrahlung= more quantity
2. Higher Z= Different atomic number= Change in Quality
How does increasing kVP affect quality and quantity?
- Increased max energy
- Increased average X ray energy (quality)
- Increased total x rays produced (quantitity)
What is the 15% rule?
Increased kVP by 15%, decreased mA by half to maintain same X ray density
How does a single phase generator compare to the triple phase generator?
Truple phase has more quality and quantity
What is HVL?
Amount of material needed to attenuate half the x ray
What does HVL depend on?
- Target Material
- Beam Filtration (more filtered= higher average energy= higher HVL)
- kVp
Does NOT depend on mA
what is the 10th HVL?
Thickness to attenuate X ray 90% (used for shielding)
How does a filter affect the beam energy?
Decreases quantity (less under the curve) Changes quality by increased the average energy
What is the average Bremstrahlung energy?
1/3 to 1/2 the kVP
What is an Auger Electron?
Characteristic X ray hits an outer shell electron and ejects that electron instead (most common in lighter element, soft tissues)
How do mA and kVp affect focal spot?
- Increased mA and low kVP increases focal spot
2. High kVP decreases the focal spot
What is stray radiation?
The sum of leakage and scatter.
Leakage: X rays that transmit through housing
Scatter: Deflected X rays
What is the dose for DEXA
0.001 mSV
