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IE Midterm 1
| Question | Answer |
|---|---|
| What is the radiographic table made of? Why? | Cabon composite. It allows x-rays to pass through and reduces patent dose |
| What are the three components for x-ray production? | X-ray tube, operating console, and high voltage generator |
| What is inside the envelope? What does the envelope maintain? | The anode and cathode assembly (except for the stators). Maintains a vacuum |
| What is the envelop made out of? | |
| What is the envelop window made out of? | Beryllium |
| What does the protective housing do? | Controls radiation leakage and scatter (because it's lead-lined), isolates high voltage cables (preventing shock), and allows for tube cooling |
| What are the four steps to proper equipment use? | 1) measure and use appropriate SID. 2) tube, CR/collimation, and IR aligned. 3) tube and body part aligned. 4) proper kVp and mAs set |
| Is the cathode positive or negative? | Negative |
| What is produced at the cathode? | Thermionic cloud (a bunch of boiled off electrons) |
| What structures are part of the cathode? What are they made out of? | Th focusing cup which is made of nickel, and the filaments which are made of thoriated tungsten |
| What is tunsten used in the filaments? | It's a good thermal conductor, it has a high melting point, and it has a good atomic # for x-ray production |
| What is thorium added to filaments? | It helps electrons boil off (enhances thermionic emissions) |
| What controls temperature and thermionic emission in the cathode? | Current, which provides resistance to the flow of electrons in the filament |
| How hot does the filament get? | 2200°C |
| What is the space charge effect? | The electrostatic repulsion between electrons when too many have been boiled off and have nowhere to go (like charges repel); this prevents more from boiling off |
| What's saturation current? | When all available electrons have been used, so mAs must be increased to boil off more (occurs at high kVp levels) |
| How can the focusing cup act as an on/off switch? | It pulses from negative to positive, resulting in taking rapid image sequences |
| Give three examples of cathode wear | Filament wires thin/vaporize/break, tungsten deposits on inside of envelope, free gas molecules in vacuum decrease efficiency |
| What is the envelop made out of? | Image size x (SOD/SID) |
| What's the diameter of an anode disc? | 5-13 cm |
| What's the target area made of? | Tungsten |
| What materials back the target area? Why are they used? | Molybdenum because it enhances heat conduction, graphite because it's lightweight so anode can spin faster, and rhenium because it increases elasticity |
| What is the shaft made of? | Molybdenum |
| Explain the rotor and stator system | The rotor is inside the envelope, made of copper, hollow, and spins with the help of lubricated silver bearings. It's copper because copper reacts to electromagnets, which is what the stators are made of. These stators are outside the vacuum and use AC |
| What the optimal angle on a rotating and disc? | 12° |
| What's the fixed angle on a stationary anode disc? | 45° |
| What kind of anode is used in CT and angiography? | Stress relieved (rotating) |
| What happens if you increase anode RPM? | The area struck my electrons increases, so there's better heat dissipation |
| What affects focal spot size? | Filament size, filament orientation, and focusing cup shape |
| What filament size is used for low heat loads? High head loads? | Low: 0.1-1mm. High: 0.3-2mm |
| What relationship exists between angle and effective focal spot? | Smaller angle = smaller EFS size = greater image quality |
| What does the limiting factor principle state? | EFS size < AFS size, providing the anode angle is under 45° |
| What does the line focus principle state? | Smaller EFS increases spatial resolution... results in anode heel effect |
| What does the anode heel effect state? | Radiation intensity is greatest on the cathode side because the angled anode absorbs some of the photons |
| What influences the anode heel effect? | Angle (smaller angle, greater effect), IR size (larger IR, greater effect), SID (larger SID, weaker effect), effective focal spot size |
| What affects anode heat capacity? | Focal spot size, speed (RPM), anode disc diameter |
| What fills the space between the envelope and the tube housing? | Dielectric oil |
| Via what modes does hest dissipate from the anode? | Convection, conduction, and radiation |
| What is the x and y axis on tube rating charts? | X: exposure time (s), Y: kVp |
| What improves heat dissipation? | Greater RPM and larger focal spot size |
| What is the x and y axis on anode cooling charts? | X: time (minutes), Y: thousand heat units |
| How do you calculate HU for a 3 phase generator? | 1.4 × kVp × mA × s |
| How do you calculate mAs? | (ms/1000) x mA |
Created by:
Ewood61
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