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Fluoro Equipment Review RHB Fluoro Syllabus & Rad Prot

Fluoro Equipment Review RHB Fluoro Syllabus & Rad Prot. Review #1 255 June 2008 ccrt55 revised. History of fluoroscopy. Thomas Edison invented the fluoroscope in 1896 He was the first one to try to image the brain

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Fluoro Equipment Review RHB Fluoro Syllabus & Rad Prot

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  1. Fluoro Equipment ReviewRHB Fluoro Syllabus& Rad Prot Review #1 255 June 2008 ccrt55 revised

  2. History of fluoroscopy • Thomas Edison invented the fluoroscope in 1896 • He was the first one to try to image the brain • Fluoroscopy was performed in total darkness so the eyes had to be adjusted for 30 minutes by wearing red goggles

  3. General Fluoroscopic Concepts 1. Primary factors associated with fluoroscopy 2. High-level fluoroscopic procedures 3. Pulsed fluoroscopic procedures 4. Scatter, magnitude, directionality & leakage radiation 5. Dose trade offs versus quantum mottle 6. Potential image distortions

  4. Basic “Imaging Chain”

  5. Basic Componets of “old” Fluoroscopy “Imaging Chain” Primary Radiation EXIT Radiation Fluoro TUBE PATIENT 105 Photospot Image Intensifier Image Recording Devices ABC Cassette Fiber Optics OR CINE CONTROL UNIT VIDICON Camera Tube TV

  6. Basic Componets of “NEW DIGITAL” Fluoro“Imaging Chain” Primary Radiation EXIT Radiation Fluoro TUBE PATIENT Analog to Digital Converter ADC Image Intensifier ABC CCD TV

  7. Modern fluoroscopic system components

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

  9. VACUUM TUBE ENCASED IN A LEAD HOUSING = 2MM PB (PRIMARY BARRIER) Image Intensifier

  10. CsI crystals grown linear and packed closely together The column shaped “pipes” helps to direct the Light with less blurring Converts x-ray photons to visible light Cesium Iodide (CsI) Phosphoron Input Phosphor SIDE VIEW

  11. Input phosphor • X-rays hit this concave surface first. • It is made of cesium iodide crystals shaped like tiny needles packed tightly together. • The more crystals, the better the spatial resolution. • The crystals convert the x-ray photons to light energy so the more crystals, the more energy converted to light the less radiation needed so patient dose goes down.

  12. photocathode • The photocathode is close to the input phosphor but can’t touch it otherwise there would be a chemical reaction that would destroy the phosphor. • The photocathode is made of antimony and cesium compounds. When these compounds come into contact with light they emit electrons • The photocathode has the job of turning the light into photoelectrons.

  13.   Scatter in the form of x-rays, light & electrons can reduce contrast of an image intensifier tube. Veiling glare

  14. Functioning of Image Intensifier

  15. Intensifier Format and Modes Note focal point moves farther from output in mag mode

  16. BG = MG X FG • FLUX GAIN – increase of light brightness due to the conversion efficiency of the output screen • 1 electron = 50 light photons is 50FG • Can decrease as II ages • Output phosphor almost always ____ inch • Made of _____________phosphor • Flux gain is almost always 50

  17. Raster pattern scan lines Video Field Interlacing

  18. Horizontal resolution • The number of dots on the horizontal scan line. • How close together are they? • It is the product of scan lines, frame rate and frequency rate

  19. Vertical resolution • How far apart are the horizontal scan lines? Since we can’t have more than 525 scan lines, we can have more dots that are smaller • The Kell factor is a component of vertical resolution. Memorize the number 0.7 and know that it is the Kell factor & part of vertical resolution

  20. Viewing Fluoroscopic Images

  21. Image Quality • Contrast • Resolution • Distortion • Quantum mottle

  22. Contrast • Controlled by amplitude of video signal • Affected by: • Scattered ionizing radiation • Penumbral light scatter

  23. Resolution • Video viewing • Limited by 525 line raster pattern of monitor • Newer digital monitors 1024 - better resolution

  24. Size Distortion • Affected by same parameters as static radiography • Primarily OID • Can be combated by bringing image intensifier as close to patient as possible

  25. Shape Distortion • Geometric problems in shape of input screen • Concave shape helps reduce shape distortion, but does not remove it all • Vignetting or pin cushion effect

  26. Image distortion PINCUSHION EFFECT PINCUSHION ?? WHAT IS VIGNETTING??

  27. Image Quality • Terms that are necessary to know: • Vignetting is the loss of brightness at the periphery of the II due to the concave surface • Pincushion effect is the drop off at the edges of the II due to the curved surface • Quantum mottle is the grainy appearance on the image due to statistical fluctuations • The center of the II will always have the best resolution. • Lag is the blurry image from moving the II too fast

  28. Regulations about the operation • Fluoroscopic tubes operate at currents that range from0.5 to 5 mA with 3 - 4 the most common • AEC rate controls: equipment built after 1974 with AEC shall not expose in excess of 10 R/min; equipment after 1974 without AEC shall not expose in excess of 5 R/min

  29. Other regulations • Must have a dead man switch • Must have audible 5 min. exposure timer • Must have an interlock to prevent exposure without II in place • Tube potential must be tested weekly • Brightness/contrast must be tested annually • Beam alignment and resolution must be tested monthly • Leakage cannot exceed 100mR/hr/meter

  30. more regulations • Must have a device to prevent operation at a SOD of less than 12” • A bucky slot cover must be provided • Aprons must be at least 0.25 mm Pb equivalent • 2.5 mm Al equivalent filtration is required • Must provide at least 12” and preferably 15” between source and table top

  31. Fluoroscopy exposure rate • For radiation protection purposes the fluroscopic table top exposure rate must not exceed 10 mR/min. • The table top intensity should not exceed 2.2 R/min for each mA of current at 80 kVp

  32. Patient Protection • A 2 minute UGI results in an exposure of approximately 5 R!! • After 5 minutes of fluoro time the exposure is 10-30 R • Use of pulsed fluoro is best (means no matter how long you are on pedal there is only a short burst of radiation) • ESE must not be more than 5 rads/min • W/0 AEC 10 WITH & 20 BOOST

  33. Always keep the II as close to the patient as possible to decrease dose • Highest patient exposure happens from the photoelectric effect (absorption) • Boost control increases tube current and tube potential above normal limits • Must have continuous audible warning • Must have continuous manual activation

  34. ESE FOR FLUORO • TLD PLACED AT SKIN ENTRACE • POINT for fluoro • 1 – 5 R/MINUTE AVE IS ________R/MIN

  35. ESE FOR FLUORO • TLD PLACED AT SKIN ENTRACE POINT • 1 – 5 R/MINUTE AVE IS 4 R/MIN • (now closer to 1 – 3 R/min) • When not known – assume 4 R

  36. Framing and patient dosesyll = Pg 31 which is BEST • The use of the available film area to control the image as seen from the output phosphor. • Underframing • Exact Framing, (58 % lost film surface) • Overframing,(part of image is lost) • Total overframing

  37. EXPOSURE RATES FLUORO • MA IS 0.5 MA TO 5 MA PER MIN • AVE DOSE IS 4 R / MIN • IF MACHINE OUTPUT IS 2 R/MA/MIN = WHAT IS PT DOSE AT 1.5 MA FOR 5 MIN STUDY?

  38. DOSE REGULATIONS • BEFORE 1974 - AT TABLETOP • 5R/MIN (WITHOUT AEC) • 5R/MIN (WITHOUT AEC) – BOOST MODE • After 1974 with AEC • 10 R/MIN 20R/MIN BOOST

  39. ISOEXPOSURE CURVES

  40. Where should a dosimeter badge be worn?

  41. RHB “RULES” RHB RP PG61 • LICENTIATES OF THE HEALING ARTS (MD, DO, DC, DPM) • MUST HAVE A • RADIOLOGY SUPERVISOR & OPERATORS PERMIT & CERTIFICATE • TO OPERATE OR SUPERVISE THE USE OF X-RAYS ON HUMANS • SUPEVISORS MUST POST THEIR LICENSES

  42. RHB “RULES” RHB RP PG62 • ALL XRAYS MUST BE ORDERED BY A PHYSICIAN • VERBAL OR WRITTEN PRESCRIPTION • See Section C – “Technologist Restrictions”

  43. Declared Pregnant Worker • Must declare pregnancy – 2 badges provided • 1 worn at collar (Mother’s exposure) • 1 worn inside apron at waist level Under 5 rad – negligible risk Risk increases above __________rad Recommend abortion (spontaneous) 25 rad • (“Baby exposure” approx 1/1000 of ESE • 1/50 th dose of mother***) • www.ntc.gov/NRC/RG/08/08-013.html

  44. CARDINAL RULES • TIME • DISTANCE • SHEILDING

  45. RHB – Rad Prot – CH. IX p 51 • ALARA (no minimum threshold) • STOCHASTIC EFFECTS – NON TRESHOLD (CA + GENETIC) • NON STHOCAHSTIC (DETERMINISTIC) SEVERITY OF EFFECTS VARIES WITH RADIATION DOSE (THRESHOLD) (CATARACTS, SKIN, BONE MARROW, STERILITY

  46. # 7 – Dose Response Relationships LINEAR NON THRESHOLD • ASSUMES ANY AMOUNT OF RADIATION IS CAPABLE OF CAUSING A BIOLOGIC RESPONSE • THE RELATIONSHIP BETWEEN THE RADIATION DOSE AND BIOLOGIC RESPONSE IS CONSIDERED TO BE DIRECTLY PROPORTIONAL

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