Ch. 5 XR Production Flashcards
- vacuum
- source of electrons (filament)
- target
- high potential difference (voltage)
Requirements for Xrays
-envelope
- filament
- target
Elements of tube housing
Pyrex glass forms the structure of the tube
Envelope
Tungsten is the source of electrons & is located on the Cathode side
Filament
Slanted metal surface that “attracts” the electrons towards the Anode side
Target
Heated electrons increase distance from the nucleus creating a space charge (“electron cloud”)
- space charge: free electrons in thr air
Thermionic emission
Electrons rapidly moving across the tube towards the target
Electron stream
Incoming electron (“pumps the breaks”) slows down & changes direction without interaction
-energy creates x-rays
Bremsstrahlung
Incoming electron knocks out k-shell electron out of orbit (“ out of character”)
-void being filled creates xray
Characteristic
Below 70 kvp = all interactions are brems
Above 70 kvp = 85% of interactions are brems, 15% are characteristic
How many interactions are bremsstrahlung or characteristic?
Is dual focus,
Contains 2 filaments (small & large) & a focusing cup
Cathode
A hollow area for the filament that has a slight neg. Charge allowing the electrons to repel towards the focal spot. (Actual vs effective)
Focusing cup
- Measures target surface
- larger in size to absorb heat generated for thicker body parts
- less image resolution
1.2mm
Actual focal spot
- Measures projection of the actual focal spot
- Affects image resolution
- produces better detail
0.6mm
Effective focal spot
Contains a rotating antode that uses electromagnetic induction to rotate for heat capacity
Anode
Rotating target anode
3600 rpm
Focal track
7-12 degree slant to dissipate heat & determine image sharpness
Target angle
The angle determines the size of the focal spot which determines the image resolution
Line focus principle
The variation in radiation intensity across the length of the irradiation field
(Cathode side is >)
- thin portion =too dark
-thick portion = too light
-only applies if 40” SID whole beam is used or 72” SID full spine
Anode Heel Effect
Remove the long wave length photons from x-ray beam and reduces patient dose
- Placed between the tube and the patient
Filtration
Aluminum = added (2 mm)
Glass housing & oil= inherent (0.5mm)
2.5 mm AL eq. Total filtration
Added vs inherent filtration.
Controls PENETRATION & CONTRAST (AKA:QUALITY)
(high contrast = low kvp, low contrast = high kvp)
kVp
Controls QUANTITY of CURRENT FLOW, & image DENSITY (brightness)
(If doubled, x-ray is doubled; if halved, x-ray is halved)
mAs
