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Fluoroscopy Notes

Fluoroscopy Notes. Rad Tech 290. Fluoroscopy Notes Ch 1. Approximately 5% of the US population has a fluoro procedure each year The average number of fluoro exams per person is 1.3 The average number of spot films is 4.6. The MC exam is a GI tract at 53%

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Fluoroscopy Notes

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  1. Fluoroscopy Notes Rad Tech 290

  2. Fluoroscopy Notes Ch 1 • Approximately 5% of the US population has a fluoro procedure each year • The average number of fluoro exams per person is 1.3 • The average number of spot films is 4.6

  3. The MC exam is a GI tract at 53% • A 2 minute UGI exam can produce an exposure ranging from 5-15 rads, comparatively a KUB is between 100-500 mrads. • Fluoro is defined as a rad exam utilizing fluorescence for the observation of the transient image.

  4. Fluoro was first used as a dynamic procedure. Second as a means of positioning for spot films. • Medical exposure accounts for about 20% of the total radiation people receive. • Even though the percentage is small, for medical exposure, it is the only exposure that is controllable. • FLUOROSCOPY TO POSITION PATIENTS IS PROHIBITED.

  5. Notes Chapter 2Factors Directly Affect Exposure • mA • kVp • Collimation • Filtration • Exposure time • Total fluoro time • Target to panel distance (TPD) • Patient to II distance • Sensitivity of the image receptor • Essentially speed RSV

  6. The following will reduce exposure • Collimating • Last frame hold • Shortest possible patient to II distance • Highest possible kVp • Pulsed fluoroscopy • Using the largest II mode with collimation

  7. Factors indirectly influencing exposure • Room illumination • Image receptor quality • Absorption of the table top

  8. mA • 0.5 – 5 mA • Usually 1 – 3 mA • Spot films • 100 mA or higher • Output and dose are directly proportional to mA

  9. kVp • Maximum photon energy • Beam quality • Penetrability of the beam • Tube potential

  10. collimation • Required by law • Image quality improves as the beam is collimated

  11. Collimation Collimate tightly to the area of interest. • Reduces the patient’s total entrance skin exposure. • Improves image contrast. • Scatter radiation to the operator will also decrease.

  12. Factor affecting staff doses FIELD SIZE DEPENDENCE Scattered dose rate is higher when field size increases 11x11 cm 17x17 cm 17x17 cm 100 kV 0.8 mGy/h 1.3 mGy/h 1 mA 0.6 mGy/h 1.1 mGy/h 0.3 mGy/h 0.7 mGy/h 1m patient distance Patient thickness 18 cm

  13. filtration • If the tube is operated above 125 kVp, 3 mm Al eq is required. • Filtration reduces patient dose

  14. Source to table toptarget to panel distance • Cannot be less than 12” and should be 18” • Mobiles are required to be at least 12” • Fixed units, 15”

  15. Patient to II distance • The closer the II, the lower the dose • This is more pronounced with fixed units. • Decreases the SID

  16. Tabletop • Less than 1 mm Al eq at 100 kVp • Exposure switch • Dead man type

  17. Primary protective barrier • The II is the primary barrier and must have 2 mm Pb eq for systems operating above 125 kVp • The II has to be in place for the tube to energize

  18. Protective Actions • Bucky Slot Cover • Automatically covered, 0.25 mm Pb eq • Protective curtains • 0.25 mm Pb eq • Not required on c-arms • Scatter at 1 foot can reach 500 mrad/hr

  19. Allowable exposure rates • Cannot exceed 5 rad/minutes • Unless, ABC or image recording • Cumulative timer • Cannot exceed 5 minutes • Illumination

  20. II Considerations • Purpose • The basic purpose of the II is to make the fluoro image brighter • When the image is brighter it is easier to visualize structures • Brightness Gain • Minification gain multiplied by electronic (flux) gain

  21. II Facts • Input phosphor, cesium iodide • Photcathode, danium antimony • Output phosphor, zinc cadnium sulfide

  22. Image Quality Issues • Quantum Mottle • Caused by too few photons • Contrast • Subject • Detector • Image • Resolution

  23. Effect of X ray Beam Penetration on Contrast, Body Penetration, and Dose t

  24. 15 µR per frame 24 µR per frame Dose vs. Noise 2 µR per frame

  25. Distortion • Size, shape, pincushion • Lag • Vignetting • Less bright at the edges than center of image • Magnification tubes, Multi-mode • Variable FoV

  26. Closed Circuit TV Systems • Camera • MC is the vidicon • Camera control unit • Video amplifier • Monitor • CRT, etc.

  27. Cinefluoroscopy • Synchronization • Record with the x-ray pulses • Framing frequency • Division of 60 • The higher the rate the higher the dose • F-number • Video disk recording (electronic radiography) • Exposure ends when image is formed • Basically fluoro phototiming • 95% dose reduction

  28. Video tape • Instant playback and no additional dose • Spot films • Conventional cassettes • Photospot cameras • ½ to 1/3 dose of convent. Cass. • Lower image quality

  29. Accessories • Gonadal shields • Required when possible • Grids • Fluoro uses low ratio grids • Cassettes • Cine film • Per frame basis 10 x the dose than fluoro

  30. Factors affecting an Increase in Scatter • High kVp • Large field size • Thick body part

  31. Advantages of 3 phase and medium/high frequency generators • Relatively high mA • Higher effective kVp • Near constant potential • Less ripple

  32. Notes for Chapter 3 • Fluoro Image Production • Fluoro units have 2 basic components • X-ray tube • Image intensifier

  33. Fluoro X-ray Tube • Regular rotating anode x-ray tube • Runs at a lower mA • Less than 5 mA • Small focal spot • Possible because of the low mA

  34. II • The primary purpose is to increase the brightness of the fluoro image • Components • Glass envelope that provides a vacuum • Input layer • Converts x-ray photons to electrons • Electronic (electostatic) lens • Output layer

  35. Input layer • Converts x-ray photons to light photons • Light photons then strike the photocathode and convert into electrons • Electrons are then accelerated across the II • Electrons strike the output phosphor and are converted back into light photons

  36. The image intensifier (I.I.) I.I. Input Screen Electrode E1 Electrode E2 Electrode E3 Electrons Path I.I.Output Screen Photocathode +

  37. Image intensifier component • Input screen: conversion of incident X Rays into light photons (CsI) • 1 X Ray photon creates  3,000 light photons • Photocathode: conversion of light photons into electrons • only 10 to 20% of light photons are convertedinto photoelectrons • Electrodes : focalization of electrons onto the output screen • electrodes provide the electronic magnification • Output screen: conversion of accelerated electrons into light photons

  38. Image Intensifier Magnification Modes Same area Output phosphor Input Phosphor 9 inch field 6.5 inch field

  39. 12" (32 cm) 100 9" (22 cm) 200 6" (16 cm) 300 4.5" (11 cm) 400 RELATIVE PATIENT ENTRANCE DOSE RATE FOR SOME UNITS IMAGE INTENSIFIER Active Field-of-View (FOV)

  40. Brightness Gain • BG is the product of minification gain and flux(electronic) gain • Minification Gain • Input phosphor dia.2/output phosphor dia2 • Making the image smaller will make it brighter. • The same number of photons are contained in a smaller area • In most IIs the output phosphor is 1 inch.

  41. Flux Gain • Caused by the conversion efficiency of the output phosphor and the acceleration of the electrons across the II • As the electrons accelerate they gain kinetic energy • Flux gain is usually between 50 and 150.

  42. Measuring Brightness Gain • The actual measurement is done by calculating the conversion factor • Intensity of output phosphor (candelas)/mrads/sec • Brightness gain will deteriorate 10% annually. • This will ultimately decrease image contrast

  43. Beam Splitter Mirror • 10% of the output light goes to the vidicon (video camera) the remainder goes to the photospot device. • NOTE: not all units have a beam splitter

  44. Vignetting and Pincushion Distortion • Pincushion • The loss of shape at the edges of the fluoro image • Vignetting • Loss of brightness at the edge of the image

  45. Veiling Glare • Occurs when the light from the output phosphor ‘reflects’ back into the II. • Remember, the photocathode is stimulated by light, so light ‘reflecting’ from the output phosphor would also trigger electron production. • Decreased contrast results

  46. Automatic Brightness Stabilization (ABS)Automatic Brightness Control (ABC) • Keeps light output of the II constant. • Brightness of the image varies with changes to kVp and mA. • Increase mA increase brightness; direct relationship • Increase kVp 10% double brightness

  47. Brightness Sensing • II photocathode current • Television camera signal sensing • Lens coupled phototube sensing

  48. Types of ABS • Variable mA, preset kVp • Set the kVp and the unit adjusts mA • Variable mA with kVp following • If the mA range is exceeded the unit will automatically adjust the kVp to compensate • Variable kVp, preset mA • Set the mA and the unit adjusts kVp • Variable kVp, variable mA

  49. Closed Circuit TV Systems • Camera • Camera control unit • Power supply and video amplifier • Monitor

  50. Cameras • Vidicon • MC, inexpensive, lag, 525 raster lines • Plumbicon • Cardiac cath labs • Fixed gain (better contrast) and low lag • Increased quantum mottle • Image orthicon • Not widely used • CCD • Solid state semiconductor • Small, low power consumption, low price, long life

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