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Fluoroscopy
Bushong Chapter 25
| Question | Answer |
|---|---|
| In what order does the human eye receive light to the retina? | Goes through the cornea, iris (opens or closes), lens, then reaches the retina. |
| Where is the retina located in the eye ball? | In the back |
| What is contain in the retina? | Rods & Cones |
| What do we use our rods for? | Night vision |
| What is another name for night vision? | Scotopic Vision |
| What is the min lux required for the rods to start working? | 2 lux |
| Where are the rods located in the retina? | In the peripheral |
| What do we use our cones for? | Day vision |
| What is the min lux required for the cones to start working? | 100 lux |
| Where are the cones located in the retina? | In the center |
| What is another name for day vision? | Photopic vision |
| What is the center of the retina called? | Fovea centalis |
| What are the cones responsible for? (2 things) | 1. visual acuity 2. contrast perception |
| What is illumination measure in? | lumens per square meter OR lux |
| Radiographs are visulaized between ___-___lux (a number) | 100-1000 |
| What is illumination? | light from a source hitting your eye. |
| Before image intensification what 4 things were going on? | 1. exams done in the dark 2. image was more inferior (b/c it was pure xrays) 3. procedures took longer 4. misdiagnosis were common |
| Image intensified fluoroscopy developed to raise __________ of an image into ______ vision region to maximize ______ _______ | illumination, cone, image detail |
| What 3 things does the brightness of a fluoro image depend on? | 1. kVp 2. mA 3. anatomy |
| Generally _____ kVp and _____ mA are preferred. Why? | High, low. Low mA because the exam time is longer than a normal xray. |
| What does ABC stand for? | Automatic Brightness Control |
| What does ABC do? | Automatically adjusts for part thickness to minimize patient dose and maintain consistent brightness. |
| When the ABC is adjusting to maintain the consistent brightness, which is adjusted first? | kVp |
| Who uses/controls the use of the automatic brightness control? | The radiologist. |
| What mA is fluoro usually using? | 5mA or below. |
| With fluoro is patient dose increased or decreased? Why? | Increased because the exposure time is much longer. |
| How do you determine what kVp to use for an exam? | The body part |
| What is an image intensifier? (textbook definition) | A complex electronic device that receives the IMAGE-FORMING XRAY BEAM and converts it into a visible-light image of high intensity. |
| What is meant by "image forming xray beam"? | Transmitted xrays or exit radiation |
| What are the 7 parts of the image intensifier? | 1. metal tube housing 2. glass envelope 3. input phosphor 4. photocathode 5. electrostatic lenses 6. anode 7. output phosphor |
| What is the input phosphor made of? What is its purpose? And what is the range of size? | Cesium Iodide. Converts xray photons into light photons. Ranges in size from 10cm-35cm. |
| What is the photocathode? What is its purpose? What is it responsible for? | Cesium and antimony compound. Capture light and convert it into electrons. (photoemission). Photoemission. |
| In photoemission increased xray beam = | increased light = increased e- production. |
| The amount of e- produced is determined by? | The strength of the beam leaving the patient. |
| Where are the electrostatic focusing lenses located? What do they do? What type and amount of charge do they have? | Along the sides and run the length of the image intensifier. They speed up and focus the electrons. Negative charge of 25kV (or 25,000V) |
| Describe the anode. What type of charge does it have? | Circular plate with a hole in the middle to allow e- to pass to the output phosphor. Positive charge. |
| What is the output phosphor made of? What does it do? And what is the size range? | Zinc cadmium sulfide. e- interact with the O.P. at increased energy levels and contain the image of the I.P. in minified form. Ranges from 2.5cm OR 5cm |
| How much more light photons with the output phosphor produce than the input phosphor? | 50-75 times more. |
| What is Flux Gain? | Ratio of light photons at output phosphor to xrays at the input phosphor. |
| What is Minification Gain? | The ratio of the square of the diameter of the I.P. of the square of the diameter or the O.P. |
| What is Brightness Gain? | The ability of the image intensifier to increase the illumination level from input to output. |
| What is the formula for Flux Gain? | FG= light photons(I.P.)/ incident xrays(O.P.) |
| What is the formula for Minification Gain? | MG= (D1) squared/ (D2) squared |
| What is the formula for Brightness Gain? | BG= FG x MG |
| What is conversion factor? | Ratio of illumination intensity at O.P. to radiation intensity of incident xrays on the I.P. |
| What is the formula for Conversion Factor? | O.P. illumination (cd/m squared) / input exposure rate (mR/s) |
| Most image intensifiers have ____-_____ BG that decreases with tube age and use. | 5,000-30,000 |
| True or False. The Conversion Factor is s less accurate measurement than flux gain or brightness gain. | FALSE. It is MORE accurate than flux gain and brightness gain. |
| What are the ranges for the Conversion Factor? | 50-300 |
Created by:
Aborys88