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Fluoroscopy Week 2

Fluoroscopy Image Intensifier

QuestionAnswer
What year was the Image Intensifier developed? 1948
Why is there a loss of detail with video system fluoroscopy in comparison optical mirror viewing systems? Image noise from transferring the image resulting in loss of detail.
How much do modern Image Intensifier's increase image brightness?When does Photopic (Cone) vision become active? 500-8000x. Photopic vision becomes active at about 1000x.
What is the arm that's suspended over the table that supports the image intensifier called? The Carriage
What is typically included on the carriage? Image Intensification Tube, Controls for driving, Brightness control, Spot Film selection/Cinecamera, Video Input tube & Tube Shutters.
What does brightness control regulate? Regulates the x-ray tube mA?
What do federal regulations prohibit in regards to fluroscopy x-ray tube and primary beam? What is done to avoid this from happening? Federal regulations prohibit the use of fluoroscopy x-ray tube when entire primary beam is not resulting in exposure. An exposure cannot be made until carriage is returned to full beam intercept position & locked in place.
Why does the C-Arm allow the IR to be raised and lowered? Why should the Image Intensifier be as close to the patient as possible? To vary beam geometry for maximum resolution. TO reduce exposure to the operator from scatter by the patient.
The fluoro x-ray tube target is fixed to prevent an SOD of less than what? The fluoro x-ray tube target must be fixed to prevent an SOD of less than 15".
What are the 4 principal components of an Image Intensifier? Vacuum Bottle/Glass Enevelope, Input Layer, Electronic Lenses & Output Phosphor.
What does the primary x-ray beam strike after it exits the patient on a fluroscopy x-ray tube? Primary x-ray beam strikes the input phosphor after exiting the patient?
What fluorescent material is the Input phosphor made of? Cesium Iodide (CsI)
What happens at the input phosphor? How much of the incident beam is absorbed by the CsI? The x-ray photon from the primary beam is absorbed by CsI and converted into a light photon. 66% of the incident beam is absorbed by CsI.
What process happens at the photocathode? What is being converted? What are the steps in this process? Photoemission. The photocathode takes light energy and converts it to electrical energy. The photocathode absorbs light photons from the input phosphor and emits electrons.
Where are the emitted electrons from the photocathode directed to? Towards the anode end of the Image Intensification tube?
What happens at Electronic Lenses of the Image Intensification tube? How does the lens accelerate the electrons? The Elecctronic Lenses focus & accelerate the elctrons from the photocathode. The Electronic Lens is negatively charged which repels the electrons accelerating & focusing them towards the much smaller output screen.
What is the potential difference from the photocathode to anode & output screen? 25,000 V or 25 kV.
Is the # of electrons emitted by the photocathode directly proportional to the intensity of light reaching it? Yes
Where does the primary brightness gain occur from? Why is this? From the acceleration & focusing of the electrons at high voltage. The acceleration of the beam increases its energy & ability to emit light at the output screen. The focusing of the electrons intensifies the image into a smaller area.
What is the Anode? Where is the Anode of the Intensification Tube positioned? The Anode is a circular plate with a hole in the middle to allow electrons through to go to the output phosphor. The Anode is positioned in the glass envelope in front of the output screen.
What is Anode usually charged? What voltage is it usually supplied from and from where? The Anode is usually positively charged. It's usually supplied with 25 kV from the negatively charged photocathode.
What fluorescent material is the output screen made of? Zinc Cadmium Sulfide
What does the output screen do with the incoming electrons and where do the electrons come from? The output screen absorbs the electrons from the photocathode that went through the electronic lenses through the hole in the Anode. The output screen converts the electrons into light photons.
How many light photons are emitted at the output phosphor? How many times brighter is the output phosphor than the input phosphor? 3000 light photons. 1000x brighter.
How many light photons are converted from 1 x-ray photon at the Input phosphor? 1000 light photons from 1 x-ray phton.
What is the size of the output phosphor? The output phosphor is generally 1".
What are the typical input screen sizes? 6", 9" & 12"
What does minification gain occur as a result of? What is the formula for minification gain? The same # of electrons that were produced at the input phosphor being compressed into the area of the output screen? MG=Distance 1 squared/Distance 2 squared.
What is Flux Gain? A measurement in the increase of light photons due to conversion efficiency of the output screen. In simple terms "How many light photons are produced at the output phosphor for each electron that strikes it?"
What does Flux Gain vary from? 50-150 depending on manufacturer specifications.
What is Total Brightness Gain? What is the formula? The measurement of the increase in Image Intensity achieved by the Image Intensification tube? BG=MGxFG
How much does Brightness Gain decrease per year? Why is this? As much as 10% per year. Input & Output phosphors age.
What is the Conversion Factor? What is the formula? The ratio of intensity of the output phosphor to the input exposure rate to the input phosphor? Conversion Factor = FG/mrads per sec from input phosphor
How does the magnification work on the multifield image intensifier tubes? When the input phosphor diameter changes the focal point moves from the output phosphor.
What is the Magnification Factor? MF = Diamter 1/Diamter 2
Created by: jamestkelley
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