RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY

1. IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology RADIATION PROTECTION INDIAGNOSTIC ANDINTERVENTIONAL RADIOLOGY Part 19.06: Optimization of protection in Mammography Practical exercise

2. Overview • 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 19.06 : Optimization of protection in Mammography

3. IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology Part 19.06: Optimization of protection in Mammography Focal Spot Size measurements

4. Focal spot size – Required equipment 1 - Star pattern 2 - Resolution bar pattern 3- Pinhole and slit camera 6X magnifying loupe and reticule 19.06 : Optimization of protection in Mammography

5. 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 mammography screen-film cassette 19.06 : Optimization of protection in Mammography

6. Focal spot size (star pattern) (2) • Select the focal spot size, 28 kV, and an mAs to obtain an optical density between 0.80 and 1.40 (measured in the central area of the image) • The image 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 19.06 : Optimization of protection in Mammography

7. Focal spot size (star pattern) (2) (cont’d) • Remove the compression device and place the test stand on top of the bucky (breast table) • Place the test device on top of the cassette 19.06 : Optimization of protection in Mammography

8. Focal spot size (star pattern) (2) (cont’d) • According the IEC 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 19.06 : Optimization of protection in Mammography

9. 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 19.06 : Optimization of protection in Mammography

10. Focal spot size (star pattern) (2) (cont’d) The focal spot size is calculated as: where : θ : the angle of the radiopaque spokes (1° or 0.5°), Dblur : the diameter of the blur. Mstar : the magnification factor determined by taking the ratio of the diameter of the star pattern on the acquired image (Dimage) to the diameter of the star pattern (Dstar) 19.06 : Optimization of protection in Mammography

11. Focal spot size (slit camera) (1) • To determine the focal spot dimensions (f) with a slit camera, a 10 μm 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 measuring each image using an a 6X magnifying loupe with a reticule and correcting for the magnification factor according to: f = F/Mslit 19.06 : Optimization of protection in Mammography

12. 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:The method requires a higher exposure than the star pattern method. 19.06 : Optimization of protection in Mammography

13. Focal spot size(pinhole) (1) • To determine the focal spot dimensions (f) with a pinhole, a 30 μm 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 measuring the image with a 6X magnifying loupe and a reticule, and correcting for the magnification factor according to: f = F/Mpinhole 19.06 : Optimization of protection in Mammography

14. Focal spot size Pinhole camera images of focal spot 19.06 : Optimization of protection in Mammography

15. 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:The method requires a higher exposure than the star pattern method. 19.06 : Optimization of protection in Mammography

16. Where to Get More Information European protocol for the quality control of the physical and technical aspects of mammography screening. http://euref.org/index.php?option=com_phocadownload&view=category&id=1&Itemid=8 American College of Radiology Mammography Quality Control Manual, Reston VA, 1999. Quality Control in Diagnostic Imaging, Gray JE, Winkler NT, Stears J, Frank ED. Available at no cost. http://www.diquad.com/QC%20Book.html 19.06 : Optimization of protection in Mammography