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Fluoroscopy
Ch 21 Bushong
| Question | Answer |
|---|---|
| Fluoroscopy was invented when and by whom | Thomas Edison 1986 |
| Fluoroscopy is 4 | Real-time viewing of anatomical structures Dynamic studies showing motion Contrast is generally used to highlight structures Spot films can be taken during the dynamic study w/o stopping the study |
| Fluoro operation 5 | The tube operates at less than 5mA kVp is dependent on the body being examined SOD is fixed at 15” Operated by a foot switch (dead man type) ABC |
| Image intensifier | Receives the image-forming x-ray beam and converts it into a visible-light image of high intensity |
| Components of II are where and are used for what | -contained in a glass or metal envelope -Provides structural support -Maintains a vacuum |
| 6 Parts of II | -Input phosphor -Photocathode -Electrons -Electrostatic lenses -Anode -Output phosphor |
| The Input screens surface ranges from | 6” (15 cm) to 23” (58 cm) in diameter |
| Input screen | 0.1 – 0.2 mm layer of Sodium-activated Cesium iodide (CsI) phosphors coated onto the concave surface of the I.I. tube. |
| Csl crystals do what | crystals absorb about 66% of the incident beam, producing a good conversion efficiency or quantum yield |
| A single 25keV photon would produce | over 1,500 light photons |
| What is the input screen concave | Reduce distortion |
| Electrostatis lenses are | A series of charged electrodes located inside the glass envelope of the tube |
| The charge of the lenses | accelerates and focuses the electron stream, which carries the fluoroscopic image. Electrodes are - |
| Focal point does what | As with an optically focused image, the focal point reverses the image so the output screen image is reversed from the input screen image |
| Higher V for Electrostatis lenses | the greater the acceleration and the closer the focal point moves toward the input screen |
| I.I. tubes can be designed to | magnify the image electronically by changing the voltage on the electrostatic lenses. |
| Another name for mag tubes 4 | multi-field, dual-field, triple field or quad-field intensifiers |
| Increased voltage focuses the electrons | at a point closer to the input screen which causes the image to be magnified when it reaches the output screen |
| Mag iis are capable of | 1.5 – 4 times magnification, This is controlled at the fluoro carriage |
| Tubes are described according to | the diameter of the area of the input screen that will be imaged. |
| a 23/15 dual-focus tube has | a 9”(23 cm) input screen when operating normally and uses a 6” (15cm) area when magnified |
| Magnification = | input screen diameter/diameter of input screen during magnification |
| The anode is usually supplied with how much kv | 25 |
| The anode causes tremendous | tremendous attraction of the (-) charged electrons from the photocathode |
| Anode located where | inside the glass envelope, in front of the output screen |
| Middle of anode | a hole in the center that permits the accelerated electrons to pass through the anode field onto the output screen |
| Output screen is also a | glass fluorescent screen |
| Output screen is | silver-activated zinc-cadmium sulfide phosphor (ZnS-DcS:Ag) |
| The electrons that strike the screen are | converted into light photons that exit the tube |
| Because all phosphors emit light ____, | isotropically, an opaque filter is used under the output phosphor layer to prevent light from returning to the input screen |
| some units use ____ instead of glass output screen | a fiber optic disc |
| Fiber optics eliminates | the isotropic emission problem and are capable of transmitting the image some distance without loss of resolution |
| After the xrays exit the pt, they are incident... | incident on the II tube with the input phosphor (CsI) |
| When the x-ray interact with the input phosphor... | its energy is converted into visible light |
| The photocathode is bonded to | the input phosphor |
| The photocathode is a | thin metal layer composed of Cesium and antimony that responds to the stimulation of the input phosphor light by emitting electrons. AKA photoemission |
| The number of electrons emitted is directly proportional to | the intensity of the light reaching it |
| II length and potential difference | 50 cm long and has a potential difference of about 25,000 V across the tube between the photocathode and anode so the electrons produced by photoemission will be accelerated to the anode |
| In order to maintain the electron path .... | there are several electrostatic focusing lenses along the length of the tube |
| The electrons arrive at the output phosphor | w/ high kinetic energy and contain the image of the input phosphor in minified form |
| Flux gain is | The ratio of the number of light photons at the output phosphor to the number of x-rays at the input phosphor |
| Flux gain equation | number of output light photons/number of input x-ray photons |
| Flux gain causes | decrease in image quality as a result of the penumbral effect of individual crystals |
| Minification Gain | Is the ratio of the square of the diameter of the input phosphor to the square of the diameter of the output phosphor |
| Output phosphor diameter is | standard 2.5 or 5 cm |
| Input phosphor diamter | varies from 10 to 35 cm and is used to identify I.I. tubes |
| Minification gain equation | (di /do)² Di = diameter of the input phosphor Do = diameter of the output phosphor |
| Total brightness gain | The ability of the I.I. to increase the illumination level of the image is called its brightness gain |
| The brightness gain | is simply the product of the minification gain and the flux gain |
| Brightness gain equation | minification gain x flux gain |
| The brightness gain of most image intensifiers is | 5,000-30,000; decreases with age and use |
| Brightness gain is measured in | candela per meter squared (cd/m²) |
| The radiation intensity on the input phosphor is measured in | mR/s |
| Conversion factor | is the proper quantity for expressing the intensification and is approx. 0.01 times the brightness gain |
| Conversion factor = | output phosphor illumination (cd/m²)/input exposure rate (mR/s) |
| Brightness control | Maintains the brightness of the image by automatically adjusting the exposure factors as needed according to the subject density and contrast |
| 3 names for brightness control | (ABC) automatic Brightness Control, (ADC) Automatic Dose Control & (ABS) Automatic Brightness Stabilization |
| All abc's have | a slow response time |
| 4 things that affect image quality | Contrast Resolution Distortion Quantum Mottle |
| Contrast is controlled by | increasing the amplitude of the video signal |
| Scatter and pneumbral effect image quality | Scatter ionizing radiation and penumbral light scatter in the screens and the tube itself = background fog that raises the base density which in turn reduces the visible contrast |
| The primary limitation on most fluoroscopic resolution is the | 525-line raster pattern of the video monitor |
| CsI systems are capable of | 3lp/mm |
| Optical mirror systems are capable of | 4 lp/mm |
| Size distortion is caused by | the same factors that affect static imaging, primarily OID, SID, SOD |
| Shape distortion is caused primarily by | geometric problems in the shape of the I.I. tube |
| Quantum Mottle | A blotchy or grainy appearance caused by insufficient radiation to create a uniform image |
| Quantum mottle is a problem in fluoroscopy b/c | because the units operate with the minimum number of photons possible to activate the screen |
| 3 viewing systems | Optical Mirror Viewers Video Camera Tubes Video Camera Change-coupled Devices (CCD) |
| A veiling glare signal is produced | behind the lead disc positioned on the input phosphor |
| 3 things that reduce contrast | Scatter radiation : x-ray, electrons and light; through a process called veiling glare |
| Dynamic Systems 2 | Cine Film Systems Videotape Recording |
| Static Spot Filming Systems 4 | Cassettes 105 mm Chip Film 70 mm Roll Film Videodisc Recorder |
| C-arm coupling | When coupled to a videodisc unit, both static and dynamic imaging can occur |
Created by:
rachelbeatty4