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RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY

IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology. RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY. Part 15.5: Optimization of protection in radiography Practical exercise - focal spot. Contents.

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RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY

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  1. IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology RADIATION PROTECTION INDIAGNOSTIC ANDINTERVENTIONAL RADIOLOGY Part 15.5: Optimization of protection in radiography Practical exercise - focal spot

  2. Contents • Subject matter : quality control of general radiography system • Step by step procedure to be followed to implement the considered QC test • Interpretation of results 15.5: Optimization of protection in radiography

  3. IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology Part 15.5: Optimization of protection in radiography Focal spot size measurement (star pattern method)

  4. What Minimum Equipment is Needed? • Focal spot tool : star pattern • Radiographic film • Non-screen cassette • Roll of removable tape 15.5: Optimization of protection in radiography

  5. Focal spot size (star pattern) (1) • The focal spot size measurement is intended to determine its effective dimensions at installation or when resolution has markedly decreased. For routine quality control the evaluation of spatial resolution is considered adequate • A magnified X-ray image of the test device is produced using a non-screen cassette • This can be achieved by placing the film to be exposed between two sheets of opaque film (optical density greater than 3.0) inside of the cassette. • Alternatively, a mammography screen-film system can be used. 15.5: Optimization of protection in radiography

  6. Focal spot size (star pattern) (2) • Select the focal spot size, 70 kV and an mAs to obtain an optical density between 0.80 and 1.40 above base-plus-fog (measured in the central area of the image) • Tape the star pattern to the bottom of the collimator with it centered using the collimator cross hairs and the quadrants aligned parallel and perpendicular to the anode-cathode axis. 15.5: Optimization of protection in radiography

  7. Focal spot size (star pattern) (3) • Place the cassette on the table top • Make an exposure and process the film • For digital systems the procedure is the same except that measurements are made on a digital image 15.5: Optimization of protection in radiography

  8. Focal spot size (star pattern) (4) • The magnification is determined as the ratio of the diameter of the test pattern image to the diameter of the physical test pattern. • The focal spot dimensions can be estimated from the 'blurring diameter' on the of the star pattern • The distance between the outermost blurred regions is measured in two directions: perpendicular and parallel to the tube axis 15.5: Optimization of protection in radiography

  9. Focal spot size (star pattern) (5) • The focal spot size is calculated using: p q x D blur f = x 180 ( - 1 ) M star where : q: the angle of the radiopaque spokes (1° or 0.5°), Dblur:the diameter of the blur. Mstar:the magnification factor determined by measuring the diameter of the star pattern on the acquired image (Dimage) and the diameter of the device itself (Dstar), directly on the star 15.5: Optimization of protection in radiography

  10. Focal spot size (star pattern) (6) According to the IEC Standard: • a nominal 0.8 focal spot should not exceed 1.2 mm in width and 1.6 mm in length. • A nominal 1.2 focal spot should not exceed 1.7 mm in width and 2.4 mm in length. 15.5: Optimization of protection in radiography

  11. Where to Get More Information Quality Control in Diagnostic Imaging, Gray JE, Winkler NT, Stears J, Frank ED. Available at no cost. http://www.diquad.com/QC%20Book.html 15.3: Optimization of protection in radiography

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