Rad115:Chapter 21&27-Test 1
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147 terms
Terms | Definitions |
|---|---|
 what is the purpose of a fluoroscope | 1. to perform dynamic studies 2. visualize anatomical structures in real time or motion 3. view motion and function of anatomic organs |
| p) The _______is used for examination of moving internal structures and fluids. | fluoroscope |
| Thomas A. Edison | invented the fluoroscope in 1896 |
| fluoroscope construction | zinc cadmiun sulfide screen backed by leaded glass, screens emit light in the yellow green region of the visible light spectrum |
| mirror optic image | used to view images, person's eyes have to become accustomed to the dim light |
| spot film | small static image on a small format image receptor. ex: cine |
| Fluoroscopy is routine except for its applications in | angiography |
| angiography | visualization of vessels |
| 2 main areas of angiography | neuroradiology, vascular radiology |
| where is the xray tube loc | hidden under the patient table |
| xray tube operates at what mA | 0.5mA-5mA |
| Low _____ and high ______ | mA and kVp |
| patient dose is higher even with low mA because | the xray beam exposes the patient constantly for longer time |
| kVp depends on what | section of the body and type of exam |
| principal advantage of image intensified fluoroscopy | increased image brightness |
| illumination levels are measured in | Lux, Lumen, mL (millilambert) |
| Radiographs are seen under illumination levels of | 100-1000 lux |
| cornea | transparent protective covering over the lens |
| iris | regulates amt of light that comes into the eye by its ability to dilate and contrict |
| retina | area on the internal surface of the eye where the rods and cones are loc |
| cones loc | fovea centralis |
| rods loc | periphery of the retina |
| blind spot | area where the optic never enters the eye |
| photopic vision | daylight vision (cones) |
| scoptopic vision | night time vision (rods) |
| Cones | percieve small objects much better, detects brightness levels, percieve color better |
| Rods | color blind |
| visual acuity | ability to percieve fine detail |
| contrast perception | detect differences in brightness levels |
| 5 types of brightness controls | 1.ABC-automatic brightness control 2.ABS-automatic brightness stabilizer 3.ADC-automatic dose control 4.AGC-automatic gain control 5.AEC-automatice exposure control |
| brightness of the fluoroscope depends on 3 things | anatomy being examined, mA, kVP |
| image intensifier tube | device that recieves the remnant beam and converts it to light and increases the intensity of the light |
| where are the tube components contained | glass or metal envelope |
| xrays that are incident on the image intensifier tube are transmitted through the glass envelope and interact with the ___ ____ | input phosphor |
| Input phosphor | cesium iodide-energy is converted to visible light |
| photocathode | bonded directly to input phosphor with thin transparent adhesive layer and responds to stimulation of input phosphor light by the emission of electrons |
| photoemission | emission of electrons that follows light stimulation |
| p) The ______ emits elelctrons when illumination by the input phosphor | photocathode |
| thermionic emission | electron emission that follows heat stimulation |
| The number of electrons emitted by the photocathode is _______ proportional to the intensity of ligh that reaches it. | directly |
| The number of electrons emitted is _____ to the intensity of the incident image forming x-ray beam | proportional |
| Potential difference is _____ Volts maintained across the tube b/t the photocathode and anode. | 25,000 |
| output phosphor | zinc cadmium sulfide- site where electrons interact and produce light |
| electron optics | maintains proper electron travel |
| electrostatic focusing lens | reduces the pattern of electrons to the small output phosphor |
| flux gain | ratio of the number of light photons at the output phosphor to the number of xrays at the input phosphor |
| brightness gain | ratio of illumination intensity at output phosphor |
| minification gain | ratio of the square of the diameter of input phosphor to the square of the diameter of the output phosphor |
| output phosphor size | 2.5cm-5 cm (1-2inches) |
| input phosphor size | 10-35cm |
| brightness gain of most intensifier tubes | 5,000-30,000 |
| as the intensifier tube ages ____ | patient dose increases |
| veiling glare | internal scatter radiation in the form of xrays, electrons, and light can reduce contrast of the image intensifier tube |
| multifield fluoroscopy | greater flexibility, standard in fluoro |
| Intensification tubes can be disgned to | magnify the image electronically by choosing the voltage on the electrostaic lenses |
| 4 types of tubes | multi,dualfield, triple, quadfield |
| which tube is most common | trifield tube 25/17/12 cm |
| As the focal point moves closes to the input screen the image is | magnified (patient dose increase) |
| what is the principal result of changing the diameter of the input phosphor | change in focal point to reduce FOV and then the image appears magnified |
| The use of a smaller dimensions of a multifield image intensifier tube always results in a | magnified image |
| In mag mode what results | increase contrast, spatial resolution, increase patient dose |
| To maintain the same brightness level in mag mode what happens | the ABC increases the mA which increase patient dose |
| vignetting | (pin cushion) reduction in brightness at the periphery of the image |
| what is coupled to the directly to the tv camera tube | output phosphor of intensifier tube |
| vidicon and plumbicon | tv camera tube used most often |
| tv camera tube converts | the light image from the output phosphor of the image intensifier tube into electrical signal that is sent to tv monitor, where it is recontructed on the screen |
| advantage of using tv monitor | bright level and contrast can be controlled electronically |
| 2 methods are used to electronically convert the visible image on the output phosphor of image intensifier into an electrc signal: | thermionic tv camera tube, CCD |
| electromagnetic coils in the tv camera tube used to | properly steer the electron beam inside the tube |
| glass envelope serves as | mechanical support for internal elements and maintains the vaccum |
| 5 internal elements of tv camera tube | 1.cathode 2.electron gun 3.electrostatic grids 4. target assembly 5. control grid |
| cathode | negative electrical charge |
| electron gun | heated filament that supplied a constant electron current by thermionic emission |
| electrostatic grid | further accelerates electron beam |
| target assembly | serves as an anode |
| control grid | where electron formed intor an electron beam and helps accelerate electrons to anode |
| external electromagnetic coils controls | size of the electron beam, position |
| 3 types of electromagnetic coils | deflection, focusing, alignment |
| target assembly has 3 layers | window, signal plate, target |
| window | outside layer of the taget assembly, thin part of glass envelope |
| signal plate | inside layer of the target assembly, coated on the inside of the window is a thin layer of metal or graphite |
| target | photoconductive layer of atimony trisulfide is applied to inside of signal plate layer |
| 2 methods used to couple the TV camera to the intensifier image tube | fiber optics, lens system |
| fiber optics | simplest method- compact assembly, easier to move, can withstand rough handling |
| disadvantage of fiber optics | cannot accomadate the additional optics req. for devices such as cine or photospot camera |
| lens system | not used anymore, accept cine or photospot camera |
| television monitor | video signal amplified and transmitted by cable to tv monitor, where it is transmitted back into a visible image |
| what forms one end of the closed circuit tv system | television monitor |
| 2 differences b/t closed circuit fluoro and home tv | no audio, no channel selection |
| Rad tech manipulates 2 controls | brightness, contrast |
| heart of the tv monitor | tv picture tube or CRT |
| how is the tv picture tube similar to tv camera tube | contains glass envelope, electron gun, external coils, used to focus and steer electron beam |
| how is the tv picture tube different from tv camera tube | much larger, its anode assembly consists of fluoroscent screen and graphite lighting |
| video signal in the picture tube is | modulated |
| picture tube electron beam varies in | intensity |
| lateral dispersion | ... |
| TV image is formed by | transmitted visible light image of the output phosphor of image intensifier tube into an electrical video that is created by a constant electron beam in tv camera tube. Video signal modulates the electron beam of tv pic tube and transmits that electron beam into visible image at fluoroscent screen of the pic tube |
| TV camera tube is | constant-synchronous |
| TV picture tube is | modulated |
| raster beam | movement of electron beams |
| active trace | electron beam begins in the upper left corner of screen and moves to the upper right corner creating a line of varying intensity of light as it moves |
| blanked | electron beam turned off |
| horizontal retrace | electron beam retunrs to left side of the screen |
| television field | electron beam completes |
| vertical retrace | electron beam blanked and returns to top of screen |
| interlace | movement of the electron beam |
| television frame | 2 interlaced TV fields form single frame |
| 60 Hz | 60 TV fields/s or 30 TV frames/s |
| Flicker of home movies | 16 frames/s |
| p)________uses a rate of 30 frames/s. | Video monitoring |
| Vertical resolution | number of scanned lines |
| horizontal resolution | determined by bandpass or band width |
| bandpass (bandwidth) | (Hz) frequency-number of times per sec that the electron beam can be modulated |
| For a 23 cm image intensifier, a ______ TV system provides a spatial resolution of approx _______; a ______ system provides resolution of 2lp/mm | 525 line, 1 lp/mm, 1024 line |
| what is the weakest link in fluoro | TV monitor |
| cassette loaded spot film | used with image intensified fluoro positioned b/t the patient and image int. |
| cassette loaded spot film requires | higher patient dose, produces life size format, prod images of high quality |
| photo spot camera | exposes only 1 frame without interruption up to 12 frames |
| photo spot camera recieves | image from outpu phosphor of image int tube, req less patient dose (half the pt dose of cassette loaded spot film) |
| what type of xrays are found in xray bream | brem-mostly brem and char (69 kVp or greater) |
| kVp, mAs | The ABC system maintains a consistent level of image brightness by increasing__________and/or_______. |
| ... | Wen magnifying a fluoroscopic image, the diameter of the input phosphor size is _________causing the focal spot to shift away from the anode. |
| It decreases | What happens to FOV when an image area is magnified? |
| higher patient dose | Why should the magnification mode not be used routinely? |
| thermionic tv camera, or CCD (couple-charged device) | What two devices can be directly coupled to the image int outpu phos to enable the elelectrical signal to be receiv by a vid displ monitor? |
| fiber optics or lens system | What two methods can be used to couple the ccd or tv to the image int? |
| You can't use cineography with the fiber optics method. | What is the difference btw the lens systems and the fiber optics methods? |
| approx. 25,000V | What amount of voltage is required to accelerate electrons from the photocathode to the anode? |
| better spatial resolution, better contrast resolution, and higher dose to the paitent. | When an image is magnified what happens? |
| photocathode, input phosphor, electrostatic focusing lenses, anode, output phosphor | List the components of the image intesifier tube. |
| photocathode | A thin metal layer usually composed of cesium and antimony compounds that respond to stimulation of input phosphor light by emission of electrons |
| input phosphor | light emitting material in the image intensifier that converts exit radiation into visible light (cesium iodide) |
| anode | a positively charged electrode by which electrons leave an electrical device |
| output phosphor | Site where electrons interact and produce light. Each photoelectron that arrives at the output results in approximately 50 to 75 times as many light photons as were necessary to create it. Made of zinc cadmium sulfide crystals |
| Cesium iodide | What is the material used for input phosphor? |
| Cesium or Antimony | What material is used for the photocathode? |
| zinc cadminum sulfide | What material is used for the output phosphor? |
| x-ray tube (under table or above table), table (patient), image intensifier, fiber optics or lens system, photo-spot camera or spot film, thermionic tv camera or couple charged device, tv monitor | List the components for the fluoroscopic system? |
| minification gain | an increase in light intensities as a result of the reduction in size of the output phosphor image as compared to the input phosphor image |
| ratio of the square of the diameter of the input phosphor to the square of the diameter of the output phosphor. | What is the minification gain equation? |
| the ratio of the number of the output phosphor light photons to the number of the input phosphor x-ray photons | What is the flux gain equation? |
| the product of both flux gain and minification gain | What is the brightness gain equation? |
| photoemission | electron emission that follows light stimulation |
| thermionic emission | electron emission that follows heat stimulation |
| spot-film | equipment that permits the acquisition of static images during a dynamic fluoroscopic examination; images are recorded digitally and stored electronically |
| photospot camera | Similar to a movie camera but exposes one frame at a time. Uses film sizes of 70 or 105 mm |
| it shfts | What happens to the focal spot when one increases the maginification mode? Does it shift closer or farther away from the anode? |
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