19. Optimization of protection in mammography: Part 6 (372 KB)

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  • 19. Optimization of protection in mammography: Part 6 (372 KB)

    1. 1. IAEA International Atomic Energy Agency RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY Part 19.6: Optimization of protection in Mammography Practical exercise IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
    2. 2. IAEA 19.6 : Optimization of protection in Mammograp2 Overview / objective • To be able to apply quality control protocol to mammography equipment • To measure, by different methods, the focal spot size of a mammographic installation • Interpretation of results
    3. 3. IAEA International Atomic Energy Agency Part 19.6: Optimization of protection in Mammography Focal Spot Size measurements IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
    4. 4. IAEA 19.6 : Optimization of protection in Mammograp4 Focal spot size - Measuring test object 1 - Star pattern 2 - Resolution bar pattern 3- Pinhole and slit camera
    5. 5. IAEA 19.6 : Optimization of protection in Mammograp5 Focal spot size (star pattern) (1) • The focal spot size measurement is intended to determine its physical 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 a black film (OD ³ 3) between screen and film.
    6. 6. IAEA 19.6 : Optimization of protection in Mammograp6 Focal spot size (star pattern) (2) 1. Select the focal spot size required, 28 kV tube voltage and a focal spot charge (mAs) to obtain an optical density between 0.8 and 1.4 OD base and fog excluded (measured in the central area of the image) 2. The device should be imaged at the reference point of the image plane, which is located at 60 mm from the chest wall side and laterally centred
    7. 7. IAEA 19.6 : Optimization of protection in Mammograp7 Focal spot size (star pattern) (2) (cont’d) 3. Remove the compression device and use the test stand to support the test device 4. Select about the same focal spot charge (mAs) that is used to produce the standard image of 45 mm PMMA, which will result in a optical density of the star pattern image: 0.8<OD<1.4.
    8. 8. IAEA 19.6 : Optimization of protection in Mammograp8 Focal spot size (star pattern) (2) (cont’d) • According the IEC/NEMA norm : • a nominal 0.3 focal spot should not exceed 0.45 mm in width and 0.65 mm in length • a nominal 0.4 focal spot should not exceed 0.60 mm in width and 0.85 mm in length
    9. 9. IAEA 19.6 : Optimization of protection in Mammograp9 Focal spot size (star pattern) (2) (cont’d) • The focal spot dimensions can be estimated from the 'blurring diameter' on the image (magnification 2.5 to 3 times) of the star pattern • The distance between the outermost blurred regions is measured in two directions: perpendicular and parallel to the tube axis • Position the cassette on top of the bucky (no grid)
    10. 10. IAEA 19.6 : Optimization of protection in Mammograp10 Focal spot size (star pattern) (2) (cont’d) The focal spot is calculated according to the formula : 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 f = x 180 x D (M - 1) blur star π θ
    11. 11. IAEA 19.6 : Optimization of protection in Mammograp11 f = F/Mslit Focal spot size (slit camera) (1) • To determine the focal spot dimensions (f) with a slit camera, a 10 mm slit is used. Note: Produce two magnified images (magnification 2.5 to 3 times) of the slit perpendicular and parallel to the tube axis. • The dimensions of the focal spot are derived by examining and measuring the pair of images through the magnifying glass and correcting for the magnification factor according to:
    12. 12. IAEA 19.6 : Optimization of protection in Mammograp12 Focal spot size (slit camera) (1) cont’d where: F : the width of the slit camera (Mslit) : the magnification factor determined by measuring the distance from the slit to the plane of the film (dslit-to-film) and the distance from the focal spot to the plane of the slit (dfocal spot-to-slit) Mslit = dslit-to-film /dfocal spot-to-slit NB:NB: The method requires a higher exposureThe method requires a higher exposure than the star pattern methodthan the star pattern method.
    13. 13. IAEA 19.6 : Optimization of protection in Mammograp13 Focal spot size (slit camera)
    14. 14. IAEA 19.6 : Optimization of protection in Mammograp14 f = F/Mpinhole Focal spot size (pinhole) (1) • To determine the focal spot dimensions (f) with a pinhole, a 30 mm gold/platinum alloy pinhole is used. Note: Produce a magnified image (magnification 2.5 to 3 times) of the pinhole. • The dimensions of the focal spot are derived by examining the images through the magnifying glass and correcting for the magnification factor according to:
    15. 15. IAEA 19.6 : Optimization of protection in Mammograp15 Focal spot size (pinhole) (1) cont’d where: F : the size of the imaged focal spot. (Mpinhole): the magnification factor determined by measuring the distance from the pinhole to the plane of the film (dpinhole-to- film) and the distance from the focal spot to the plane of the pinhole (dfocal spot-to-pinhole) Mpinhole = dpinhole-to-film /dfocal spot-to-pinhole NB:NB: The method requires a higher exposure thanThe method requires a higher exposure than the star pattern methodthe star pattern method.

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