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Chapter 9

Chapter 9. Concepts you already know!!!. INTENSITY = ROENTGENS AKA EXPOSURE. mAs and mR proportional? kVp and mR proportional? Distance and mR proportional? How do you “harden” the beam “The disadvantage of x-ray beam filtration is reduced image contrast owing to beam hardening.” Why?.

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Chapter 9

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  1. Chapter 9 Concepts you already know!!!

  2. INTENSITY = ROENTGENS AKA EXPOSURE • mAs and mR proportional? • kVp and mR proportional? • Distance and mR proportional? • How do you “harden” the beam • “The disadvantage of x-ray beam filtration is reduced image contrast owing to beam hardening.” Why?

  3. HALF VALUE LAYER • What is penetrability? • HIGH QUALITY VS LOW QUALITY X-RAYS • HVL See last green box on pg 155

  4. FILTRATION • Inherent • Added • What affect does added filtration have to HVL? • Compensating

  5. Chapter 10 Interaction with Matter

  6. X-RAYS AND INTERACTION WITH MATTER

  7. Low energy Medium energy High energy interact with whole atom interact with electrons interact with nuclei

  8. Classical or coherent or Thomson, Rayleigh interacts with target atom excites it DOES NOT IONIZE IT NO ENERGY TRANSFER change of direction (scatter) but no ionization little significance in diagnostic x-ray Low energy

  9. Photoelectric effect lower KvP (atomic #) inner shell electrons x-ray totally absorbed secondary/ characteristic Produces the brightness (white) on film useful Medium energy

  10. Compton Effect Increases with higher energy interacts with outer shell electron IONIZES ATOM energy divided between scattered x-ray &compton electron Scattered x-ray can go many directions not useful happens with all exams backscatter Medium energy

  11. High energy • Pair production-interaction near the nuclei • Photodisintegration-absorbed by nucleus • 1.0 MeV and 10MeV respectively

  12. What does all this mean in terms of images on the film?

  13. COMPTON VS PHOTOELECTRIC EFFECT • Compton-produces film fog • Photoelectric effect results in no x-rays reaching the film (radioopaque)

  14. DIFFERENTIAL ABSORPTION • Difference of those x-rays absorbed photoelectrically and x-rays not absorbed at all. • Radiolucent • <5% reach film • <1/2 which reach film interact • 1% of x-rays emitted produce film image

  15. WHAT IS MASS DENSITY?

  16. Contrast examination • Barium • Iodine • Air

  17. Exponential attenuation • X-ray interaction in any of the five mechanisms already note • Which are… • Exponential attenuation (pg 185 figure 12-15

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