War Machine RR Flashcards
Bremsstrahlung
Variable Distances of Interactions
Average Brems energy is equal to one third of the kVp selected
Continuous Spectrum of Energy
Majority of the Photons in X-Ray Beam
Characteristic Xrays
Incident Electron Eject an INNER SHELL
electron from the Target.
Energy of the characteristic photon is
specific to the shell and the target
Classic -69.5 K shell Tungsten
Small Minority of the Photons in the X-Ray Beam
X-Ray Production Device
Glass Enclosure / Envelope
- Maintain a Vacuum
* Allow the amount and speed of the electrons to be controlled independently.
X-Ray Production Device
Cathode
• The Filament
• The place in the device where the
electrons enter
X-Ray Production Device
Focusing Cup
Help the electron beam strike the target in an acceptable size
X-Ray Production Device
Target of tungsten
Increased Target Atomic Number (Z)
Increases Quality and Quantity
Increased kVp
Increases Quality and Quantity
Increased mAs
Increased Quantity
Increased Voltage Ripple
Decrease in Quantity and Quality
Added Filtration
Increased Quality,
Decreased Quantity
H e e l E ffe c t
Smaller Angles
Worsening Heal Effect
(steeper angle = more abmpt intensity
change)
H e e l E ffe c t
Cathode Side
Strong Side
more intense side of the beam
H e e l E ffe c t
Larger Focus to Film Distance (FFD)
Less Heel Effect
H e e l E ffe c t
Smaller Film (field of view)
Less Heel Effect
Assuming same FFD
H e e l E ffe c t
Mammo - Cathode Side on the …
Chest Wall
Target (Anode) overview
Negative Charge - Repels Electrons
Made of Tungsten
Tungsten is Used Because: Has a hiqh atomic number (A 184, Z 74) - this allows for more efficient bremsstrahlunq production
It wont’t melt (hiqh
melting temperature
(3422°c)
Rhenium is often added to tungsten: To prevent cracking at
high temperatures
Rotating Anodes will use a molybdenum stem: Molybdenum will not transmit heat to the thing that spins the target disc (rotor and bearing)
Filament (Cathode) Overview
Positive Charge - Attracts Electrons
Made of thin (0.2 mm) Tungsten wire
Tungsten is Used Because:
Has a hiqh atomic
number (A 184, Z 74)
Is a good thermionic
emitter (poops out lots
of electrons)
It wont’t melt (hiqh
melting temperature
(3422°c)
Area of Interest Cathode Side
Breast Chest Wall
CXR (AP) Abdomen (belly is denser than lungs)
Thoracic Spine (AP) Abdomen (belly is denser than lungs)
Femur (AP and lateral) Head (upper thigh is thicker)
Femur (AP and lateral) ** PEDS Knee (reduce dose to gonads)
Tibia / Fibula (AP and lateral) Knee (upper calf is thicker)
Humerus (AP and lateral) Shoulder (upper arm is thicker)
Forearm (AP and lateral) Elbow (upper forearm is thicker)
Loss of Characteristic X-Rays
If you drop the kVp below the
threshold for k shell electrons you are going to lose those characteristic peaks
X-Ray In te ra c tio n s
Compton
Major Contributor to Scatter / Fog
Involves the OUTER Shell Electron
Variable Energy Transfer
Does NOT Care About Z
Depends on Density
Dominates above 30 keV
X-Ray In te ra c tio n s
Photoelectric
Major Contributor to Image Contrast
Involves the INNER Shell Electron
“All or Nothing”
Depends on Z3
Dominates below 30 keV
G eometric Relationship
Magnification Increases With
- Greater Object to Detector Distance
2. Less Source to Object Distance
G eometric Relationship
Less Blur
- Small Focal Spot
2. Closer the object is to the detector