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Chap 6 Imaging1
The X-Ray tube. Carlton/Adler.
| Question | Answer |
|---|---|
| What 4 things are needed for the production of X-rays? | Source of electrons, target, high voltage, vacuum. |
| What is the Cathode assembly's main purpose? | To create a thermionic cloud. |
| What charge is the cathode? | Negative. |
| What is the filament made of? | Tungsten. |
| The filament length and width impact what? | Detail. |
| Focusing cup is made of what? | Nickel. |
| What is the charge of the focusing cup? | Negative. |
| What does the focusing cup do? | Compresses the thermionic cloud, houses the filament. |
| Describe the space charge effect and where it takes place. | The focusing cup has a negative charge, so the electrons of the thermionic cloud are repelled because of their negative charge. The electrons fall back onto the filament while others jump off. |
| The components of the anode assembly are? | Anode, stator, rotor. |
| What are the functions of the anode assembly? | Target surface, conducts high voltage, primary thermal conductor. |
| What is the rotating anode made of? | Tungsten-rhenium alloy. |
| Where are x-ray photons created? | The target area/focus/focal track. |
| What is the line focus principle? | when the target angle is less than 45 degrees, the effective focal spot is smaller than the actual focal spot. |
| What is the most common target angle? | 12 degrees |
| What controls the effective and actual focal spot sizes? | The effective spot is controlled by the actual focal spot, which is determined by the length of the filament. |
| What is important about focal spot sizes? | The effective focal spot is important for recorded detail. The smaller, the better image. We need a large actual focal spot to help control heat. |
| Describe the anode heel effect. | The anode side of the tube has less radiation intensity than the cathode side, about 30-40%. |
| Per the anode heel effect, which side should be positioned towards the thickest part of a body? | The cathode side should be towards the thicker portions since it has more radiation intensity. |
| What is outside of the envelope? | Stator. |
| Describe the relationship between the stator and rotor. | When the stator is energized the rotor turns. |
| What is the rotor made of? | Copper cylinder witha molybdenum stem. |
| What is the envelope made of? | Glass or metal. |
| Length of envelope? | 10" |
| What are the purposes of the housing? | Control leakage and scatter radiation, isolate high voltage, provide means to cool tube. |
| What is the housing made of? | Lead-lined cast steel. |
| What is off focus radiation? | Photons that are not produced at the focal spot are "off focus" or "extra focal" |
| Calc of heat units. | HU = kVp x mA x time |
| The use of the line-focus principle causes a problem known as the ____ effect? | anode heel effect. |
| When does melting of the anode commonly occur? | When the rotor or stator stops spinning. |
| When does cracking of the anode commonly occur? | When it hasn't been warmed up. |
| What affects the production of a thermionic cloud? | Filament diameter, length, and temp. |
| The focusing cup has what charge? | negative. |
| The area of the focal spot that is projected out of the tube toward the object being radiographed is the? | Effective focal spot. |
| Leakage radiation from the lead-lined housing must not exceed what? | 100 milirem. |
| The advantage of a high speed rotor is what? | Dissipates heat better. |