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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 15.2: Optimization of protection in radiography Practical exercise. Overview.

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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 15.2: Optimization of protection in radiography Practical exercise

  2. Overview • Subject matter : quality control of general radiography system • Step by step procedure to be followed to implement the considered QC test: • Radiation output linearity • kVp and mA “compensation” • Interpretation of results 15.2: Optimization of protection in radiography

  3. IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology Part 15.2: Optimization of protection in radiography The tube output measurement

  4. The tube output measurement Purpose : • To check that the radiation output [mGy/mAs] remains constant as the mA is varied Material: • An electronic device (multi-function meter) capable of measuring kV, time, and dose 15.2: Optimization of protection in radiography

  5. Radiation output linearity (I) Method : • Use an ion chamber or solid state detector at ~ 75 cm from the focal spot • Place some lead vinyl under the detector to standardize backscatter and protect the phototimer • Use manual mode, fixed 70 kVp and exposure time (~ 100 ms) • Measure dose at all mA settings used clinically (also useful to measure kVp) 15.2: Optimization of protection in radiography

  6. Radiation output linearity (II) Analysis : • For each exposure, calculate the mAs, then the radiation dose per mAs (this ideally should be constant) • Find the maximum and minimum values of dose/mAs • Calculate variation = (max - min)/(max + min) 15.2: Optimization of protection in radiography

  7. Radiation output linearity (III) • The variation Should be < 0.1 • If > 0.1, then check the kVp - high values of dose/mAs might be associated with high kVp • If the tube has large and small focus settings, measure linearity for each separately 15.2: Optimization of protection in radiography

  8. 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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