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RAD 255 Test 5
| Question | Answer |
|---|---|
| What decade did the image intensification came into existence? | 1952 |
| What are the 5 basic components of the ii tube? | input phosphor, photocathode, electrostatic focusing lens, accelerating anode, output phosphor |
| What does the input phosphor do? | converts the xray photons to light photons |
| What is the photocathode? | responds to the light stimulation by emitting electrons known as photoelectrons |
| What is the focusing lens? | are not really lens at all, but are negatively charged plates along the length of the image intensifier tube |
| What is the accelerating anode? | located on the opposite neck end of the tube, the accelerating anode is positively charged to attract the negative photoelectrons |
| What is the output phosphor? | is to emit light photons when struck by the photoelectrons |
| What is the fundamental purpose of the ii tube? | brighten or intensify the dim image formed on the intensifying screen into an image that can be easily seen with daytime vision |
| What is the input phosphor material ? | cesium iodide |
| What is the output phosphor material? | sliver activated zinc cadmium sulfide |
| How is the intensity of light emitted by the input phosphor is related to the amount of x-rays which strike it? | directly proportional to the amount of radiation that strikes it |
| 2 criteria that must be met in terms of the shape of the input phosphor and traveling distanced of all photoelectrons | -input phosphor must be curved in shape -photoelectrons must all travel the same distance to the output phosphor |
| how many light photons are created at the output phosphor for every 1 light photon from the input phosphor? | each photoelectron 50-125 light photons at the output phosphor |
| Where and what charge does the electrostatic focusing lenses? | positively charged, located along the length of the ii tube |
| why is the input phosphor curved? | so that the electrons on the outside edges travel the same distance as those in the center |
| what is the process of electro-focusing does to the appearance of the image? | creates an undistorted image |
| how does the size of the input phosphor compared to the output phosphor causes the image to be minification or becomes smaller? | reduction in size of the output phosphor (1-2) compared to the input phosphor (6-23) causes minification gain |
| State the 2 main reasons that intensified images gets brighter? | -flux gain -minification gain |
| Define total brightness gain: | is the measurement o the increase in image intensity achieved by an image intensifer tube, brightness gain is the process of the image intensifier tube making a dim image brighter |
| Define minification gain: | ratio of the square of the input phosphor to the sqaure of the output phosphor. It occurs due to the reduction in the size of the output phosphor compared to the input phosphor, which condenses and intensifies the light |
| Define Flux Gain: | a measurement of the increase in light photons due to the conversion efficiency of the output phosphor when struck by the photoelectrons |
| what is the formula to calculate brightness gain? | BG= Flux Gain x Minification gain |
| What is the average flux gain for an ii tube? | 50-125 |
| What is the average brightness gain for an ii tube? | 5000-30000 |
| Why is the input phosphor composed of cesium iodide that produces a quality image? | -high atomic number: allows phosphor to capture more quality x-rays to be converted to light -improved detail due to vacuum packed crystals in phosphor |
| Define multi field ii tube : | intensifier tubes are constructed to provide an option for magnification of the image. the size of an image can be enlarged by operating the tube in a mode that reduces the active size of the input |
| Define dual-field ii tube: | which has two modes of operation. the normal input phosphor measures 9 inches in diameter. to magnify the image, the 6 inch mode is selected, which draws photoelectrons only from the center 6 inches of the phosphor |
| which operational mode the image will appear the most magnified | whichever one has the smallest input phosphor |
| what is the main controlling factor of the statistical quality of the intensified image ? | resolution by the number of x-ray photons which are available to for the image |
| 2 ways in which the total number of absorbed photons at the input phosphor can be increased | increased tube mA cesium ioide phosphor |
| 2 ways that the contrast is decreased in the final intensified image | reversal of the light from output phosphor x-rays pass through input phosphor without being focused onto output |
| 2 different methods that control the brightness level of the intensified image | -Automatic Gain Control -Automatic Brightness Control |
| What is the Automatic Gain Control? | brightness is maintained electronically through the video monitor, with this method the radiation output remains constant, while the monitor electronically adjusts the brightness level |
| What is the automatic brightness control? | similar to AEC, radiation output from the x-ray tube automatically varies as the body part size changes, when a larger body part demands more radiation, the system automatically adjusts by varying KVP, mA, exposure times |
| Define Lag: | blurring of the image as the fluoroscope is rapidly from one body part to another |
| Define Peripheral distortion : | the outside edges of the image has shape distortion, similar to angling the x-ray tube. |
| Define vignetting: | is a fall off in brightness at the outer edges of the fluoro image. as the periphery of the image becomes magnified, it also looses brightness |
| 3 different terms which indicate that an ii tube is capable of magnification | multifield, dual-focus, tri-focus |
| when an smaller input phosphor is used to magnify the image, know which way the focal point moves: toward or away from the output phosphor? | moves further away from the output phosphor- which magnifies the image |
| What is the term for principle of operation of the TV camera tube? | Photoconductivity |
| What is photoconductivity? | means that it conducts current only when struck by visible light, and resists current in the absence of light |
| What are the components of the cathode ray tube? | electron gun, electrostatic grid(control grid), target plate or photoconductive layer, anode |
| What is the electron gun? | acts as the cathode of the tube- supplies electron when heated. The electron gun is a heated filament that supplies a constant electron current by thermionic emission |
| What is the electrostatic grid (control gird)? | forms the electrons into an electron beam to help accelerate the beam through the tube towards the anode |
| What is the target plate or photoconductive layer? | the target for the electron beam: the electron beam is constantly scanned across the target in search of light photons. |
| What is the anode? | provides a potential difference of 250 volts to accelerate the electrons through the tube at high speeds. Like all anodes, it is positively charged |
| What is the older type of TV camera tube? | vidicon-- most common |
| During cine, state what happens to the image as the frequency is increased or decreased? | -Increases: image resolution and patient dose increases -decreases: image resolution and patient dose decreases |
| What are the disadvantages of the mirror optics system ? | -limits radiologists movement -only one viewer at a time -brightness loss |
| What is the function of the TV camera tube? | converts light into electrical signal |
| 2 methods of coupling the TV camera to the output phosphor end of the ii tube | -fiber-optic system -lens system |
| main advantage of the beam splitting mirror | allows for auxiliary camera connections |
| which coupling method reduces patient dose? | lens system |
| Anode name for the TV picture tube | cathode ray tube -CRT |
| where does radiation exposure come from when using spot film cassette? | exposed by x-rays |
| where does radiation exposure come from when using spot film camera ? | exposed by light |
| What are various framing frequency possible during cine fluoroscopy ? | -frames per second 7.5,15,30,60 -60 is the most common |
| What has the most resolution, 1 MP or 5 MP monitor? | 5 MP, higher number is the better |
Created by:
madyep
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