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Spot Filming

Spot Filming. Cinefluorography. Fluoro Room Shielding. Radiation Areas. Spot Filming. Spot Film Cassettes Uses conventional radiographic cassettes. Bypasses image intensifier for direct exposure. Uses mA > 100 X that of photofluoro camera. Spot Filming. Spot Film Cameras

avram-murphy
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Spot Filming

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  1. Spot Filming Cinefluorography Fluoro Room Shielding Radiation Areas

  2. Spot Filming Spot Film Cassettes Uses conventional radiographic cassettes. Bypasses image intensifier for direct exposure. Uses mA > 100 X that of photofluoro camera.

  3. Spot Filming • Spot Film Cameras • Image the output phosphor of II. • Same mA as fluoroscopy (1-3 mA typically). • Exposes one frame/exposure. • Uses 70, 90, or 100/105 mm film size. • As you increase film size, increase image quality and patient dose. • Method of choice for spot filming compared to spot film cassettes.

  4. Spot Filming • Framing (matching II output size to film area) Total Overframing Overframing Exact Framing Underframing

  5. Framing and Patient Dose Reduction Underframing Exact Framing • Int. image = small dimension of frame • No part of image lost • Only 58% of frame used • Fluoro image < frame • Should be avoided P. 31

  6. Framing and Patient Dose Reduction Total Overframing Overframing • Image circle > short film dimension • Part of image lost • Circular image = diameter of frame • All of film used • 39 % of image wasted

  7. Cinefluorography • The process of recording fluoro images on movie (cine) film. • Film sizes • 16 and 35 mm • The larger the film size, the greater the resolution and greater the patient dose.

  8. Film Size 12.6 mm 30 mm

  9. Cinefluorography • Synchronization • Camera shutter timed to the same frequencyas the x-ray pulses. • Shutter open only during x-ray pulses. • Framing Frequency • Number of exposed frames/second. • Divisions or multiples of 60 Hz line rate. • Examples: 7.5, 15, 30, 90, 120 frames/second.

  10. 35 mm Cine Camera

  11. Shutter Synchronization

  12. Cinefluorography, cont’d • Framing Frequency • Patient Exposure • Directly proportional to framing frequency. P. 30

  13. Cinefluorography, cont’d • Framing Frequency • Patient Exposure Conversions • 2000 mR/frame X 1 mR/1000 mR = 2 mR/frame • 2 mR/frame X 30 frames/second X 60 seconds/minute = 3,600 mR/minute • 3,600 mR/minute X 1 R/1000 mR = 3.6 R/minute P. 30

  14. Cinefluorography, cont’d • F-number • Number indicating the ratio of the focal length of the camera lens to the diameter of the lens. • F-number = Focal Length of Lens/Diameter of Lens • The smaller the f-number = more light into the camera and less patient exposure. P. 30

  15. Focal length of lens Lens Diameter F-num =50 mm / 20 mm = F 2.5

  16. F-numbers Iris diaphragm The smaller the f-number - the larger the aperture opening. The larger the f-number - the smaller the aperture opening.

  17. Depth of field

  18. QA Concerns Spot Film and Cine Cameras • Beam and image size match within 3 % of SID • A small aperture (large f-number) will require greater patient exposure but result in low noise image. • Patient entrance exposures of 50 - 150 rads or more. P. 110

  19. Structural Fluoro Room Shielding Provisions • Barriers • Primary • A barrier to attenuate the useful beam to the required degree. • Secondary • Used to attenuate stray (scattered and leakage) radiation to the required degree. • Useful Beam • Radiation that passes through window, aperture, or cone. • Stray Radiation • Leakage and secondary radiation. No useful purpose. p. 121

  20. Primary/Secondary Barriers Exception would be in R/F room where all walls would be a primary barrier. (Source: Principles of Imaging Science and Protection. Thompson, Hattaway, Hall, Dowd, 1994)

  21. Structural Fluoro Room Shielding Provisions • Tube Leakage • Maximum exposure @ 1 meter is 0.1 R/hour. • Half-Value Layer (HVL) • Thickness of material that reduces beam exposure rate by half of original value. • Tenth-Value Layer (TVL) • Thickness of material that reduces beam exposure rate to 1/10 of original value.

  22. Tube Leakage 1 meter Maximum permissible = 0.1 R/hr. @ 5 mA

  23. Radiation Areas • Radiation Area • Any area where whole body dose could be = or > 0.005 rem/1 hr. at 30 cm from source. • High Radiation Area • Any area where whole body dose could be = or > 0.1 rem/1 hr. at 30 cm from source. • Controlled Area • Any area where radiation safety rules enforced. • Unrestricted Area • An area in which access is neither limited nor controlled.

  24. Radiation Areas, cont’d. • Restricted Area • Any area where access is limited by thelicensee to protect individuals against undue risks from radiation exposure.

  25. Unrestricted/Controlled Areas

  26. Controlled Area Unrestricted Area

  27. Spot film Cine Processor Film Cameras Flare Exposure Timer Image Lag Film-Screen Contac t QC-Semi-annual checks mAs Linearity Image Quality Exposure Reproducibility Grid Alignment Phototimers Linearity Spot Film-Cine Image Cine Film Processor Camera Exposures Cine Film Exposure Spot Film Beam Limitation Resolution –Distortion Film

  28. Video Recording of Fluoroscopic Image • Video Tape • Video Disc Laser Disc CD • Electronic Radiography DVD

  29. Video Tape • AdvantagesInstant Replay No increase in patient exposure • DisadvantagesPoor image quality Fixed framing rate- 30 frames/sec.

  30. Video Disc (Electronic Radiography) • AdvantagesLast image freeze “sticky fluoroscopy” Instantaneous imaging Short exposure times 95% dose reduction during fluoro Variable framing rates – 1-30 frames/sec. Multiple image storage Random access of images • DisadvantagesNone significant

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