Term
|
Definition
| (-), surrounds coil of cathode |
|
|
Term
|
Definition
| applied to tungsten filament, attains 2000C, units = Amps (A) |
|
|
Term
|
Definition
| electrons "boil-off" coil & form (-) charged electron cloud |
|
|
Term
|
Definition
| power dissipated = voltage x current, high resistance causes temp. to rise |
|
|
Term
|
Definition
| electrons emitted from filament form (-) cloud, retards electron emission |
|
|
Term
|
Definition
| units = mA, flow of electrons across vacuum gap to anode, electrons attracted to anode w/ increase (+) potential applied to anode |
|
|
Term
|
Definition
| at low kVp, the tube current is kVp controlled (output proportional to current) |
|
|
Term
|
Definition
| 40 kVp, all electrons are pulled away from filament & tube current is maximized (current now controlled by filament heating) |
|
|
Term
|
Definition
| target area bombarded by electrons |
|
|
Term
|
Definition
| embedded target material = tungsten (high melting point & atomic #) |
|
|
Term
|
Definition
| increased surface area dissapaites heat more efficiently |
|
|
Term
| Anode Design - sharper image |
|
Definition
| anode angled to decrease focal spot size, smaller focal point = sharper image, shallower angle = sharper image |
|
|
Term
|
Definition
| by angling anode target, the effective focal spot (area of beam projected into patient & image receptor) is much smaller than actual focal spot |
|
|
Term
|
Definition
| anode "heel" absorbs radiation producing non-uniform beam, higher intensity beam produced on cathode side (thicker body parts should be positioned toward cathode) |
|
|
Term
|
Definition
| filters out long wavelength, lower energy radiation ("soft" radiation) which "hardens" the beam; measured in mm of aluminum thickness |
|
|
Term
|
Definition
| inherent (filtering in tube head) & added |
|
|
Term
|
Definition
| combine layered Al & Cu to cut down filter thickness for higher enery beams |
|
|
Term
|
Definition
| wedge filter - great for foot; trough/bilateral wedge filter - for chest; step-wedge filter |
|
|
Term
|
Definition
| INEFFECTIVE, 99% yield useless infrared radition/heat, 1% produce useful x-rays |
|
|
Term
| 3 Anode Interactions/Radiation Types |
|
Definition
| infrared (99%), Bremsstrahlung (0.9%), characteristic (0.1%) |
|
|
Term
|
Definition
| "braking" radiation, electrons do not collide w/ tungsten anode atoms and get diverted due to opposing nuclear forces which yields a photon of radiation |
|
|
Term
| Energy of "Braking" Radiation |
|
Definition
| kinetic energy lost thru "braking" is converted to photons of equivalent energy; faster moving electrons produce higher energy, shorter wavelength photons |
|
|
Term
| Typical Polyenergetic Bremsstrahlung Curve |
|
Definition
| x-ray energy (keV) vs. # of x-rays; peaks at 1/3 of max energy |
|
|
Term
|
Definition
| electrons bambarding target "knock out" inner orbital electrons, incoming electron energy is >= to atomic shell energy, (+) charged target atom returns to normal state by emitting x-ray |
|
|
Term
|
Definition
| work required to remove electron from atom, bound particles have (-) potential energy, to free electron the energy must be raised to 0 or (+) |
|
|
Term
|
Definition
| produce radiation dose reductions & mA increases |
|
|
Term
|
Definition
| product of # of photons & photon energy, unit = Roentgen (R) |
|
|
Term
|
Definition
| term used to express intensity of beam, charge liberated per unit air mass, units = C/kg (SI system) or R (non-SI) |
|
|
