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Unformatted text preview: 1 st Week Lab Review 1. What type of glass is the x-ray tube made of: It is made out of Pyrex or ceramic materials. It needs to be able to withstand the tremendous heat that is produced during the production of x-rays. 2. The tube is a diode tube. Name the two electrodes: Positive electrode is the: anode Negative electrode is the: cathode 3. There are two filaments. What is the difference between them? One is small (short) one is large (long) 4. Describe the advantages and disadvantages of each filament: • Advantage of small: a small focal spot and therefore relatively perpendicular photons in the useful beam and a sharp image • Disadvantage of small: the small filament cannot stand much heat (is restricted to a low mA) and will therefore require a longer time of exposure for any given mAs (quantity of x- ray photons). This may result in patient motion which is the number one enemy to radiographic detail sharpness. • Advantage of large: The large filament can tolerate more heat (higher mA) due to its larger surface area. This means that a use of a high mA will require less exposure time for any given mAs. • Disadvantage of large: a larger focal spot: x-ray photons that are divergent and not perpendicular to the part, therefore less detail sharpness in the image 5. How do you select the filament/focal spot on the console? The filament is restricted by how much heat it can tolerate. Milliamperage (mA) is what sends current to the filament and causes it to heat (thermionic emission). Therefore: the low mA settings select the small filament and the high mA settings select the large filament. Think of an electric stove burner. As you select from low to medium to high it gets hotter. 6. What is the focal spot? Where is it? The focal spot is the specific area on the tungsten target of the anode that x-rays are produced. Use of a cathode small filament will make the electrons strike a small focal spot area on the tungsten target of the anode. Use of a large filament will make the electrons strike a large focal spot area on the tungsten target of the anode. See question # 4 to review the influence of focal spot size to the geometric property of detail sharpness. 7. State the term for “boiling off” electrons: Fancy terminology: thermionic emission. Get it? mA heats the filament – therm. Ionic – electrons are ions : electrons are boiled off the filament: thermionically emitted. 8. If Milliamperage is tripled: What happens to the number of electrons boiled off? Tripled What happens to the number of x-rays produced? Tripled What happens to the radiographic density? Tripled 9. Define radiographic density Blackness in the image: Specifically the mass per unit volume of black metallic silver built up in any area in the image. 10. If exposure time is tripled:10....
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This note was uploaded on 11/22/2011 for the course RADD 2501 taught by Professor Sandyeverage during the Winter '11 term at Life Chiropractic College West.
- Winter '11