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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 15.1: Optimization of protection in radiography Practical exercise. Overview / Objectives.

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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 15.1: Optimization of protection in radiography Practical exercise

  2. Overview / Objectives • Subject matter : quality control of general radiography system • Step by step procedure to be followed to implement QC test: • kVp Accuracy and Reproducibility • Interpretation of results 15.1: Optimization of protection in radiography

  3. IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology Part 15.1 : Optimization of protection in radiography kVp measurement (Accuracy and Reproducibility)

  4. kVp measurement Purpose : • Image quality and patient dose are dependent on any variation in the generator kilovoltage (kV) of the x-ray set. Therefore an accurate kV calibration is required. • A non-invasive tube voltage check over the range of kV used clinically should be performed Equipment : • An electronic device (like multi-function meter) to measure : kVp, time, dose. 15.1: Optimization of protection in radiography

  5. Multi-Function Meters 15.1: Optimization of protection in radiography

  6. kVp Accuracy • Before making measurements, one must understand what “kVp” means • There are 3 definitions of kVp, only one is commonly used • CAUTION : some mobile x-ray units use a capacitor, and the kVp decreases during the exposure 15.1: Optimization of protection in radiography

  7. kVp Definitions 15.1: Optimization of protection in radiography

  8. kVp Accuracy Method : • set meter at about 100 cm from focal spot or as prescribed by the manufacturer • set ~ 20 mAs • measure kVp from about 60 - 120 kVp (e.g., 60, 70, 80, 100, and 120) • calculate error between selected and measured value 15.1: Optimization of protection in radiography

  9. kVp Accuracy Analysis : • The difference between selected and measure kVp should be within  5% Frequency : • acceptance • tube change, generator maintenance • annual 15.1: Optimization of protection in radiography

  10. kVp Reproducibility • This test checks that the kVp will stay the same from exposure to exposure Method : • same setup, but at fixed 70 kVp • make 5 exposures about 30 seconds apart (be careful of tube load!) 15.1: Optimization of protection in radiography

  11. kVp Reproducibility Analysis : • calculate coefficient of variation (CV) • CV = (standard deviation/mean) of the 5 readings • CV must be less than 2% Frequency : • as for accuracy 15.1: Optimization of protection in radiography

  12. kVp Reproducibility Further test : • older x-ray units may have a mechanical selector for kVp • test this by moving the kVp dial up, down, then back to 70 before each exposure • a variation of  3 kVp is permitted 15.1: Optimization of protection in radiography

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