Concepts you already know!!! Chapter 8 Concepts you already know!!!

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

HALF VALUE LAYER What is penetrability? HIGH QUALITY VS LOW QUALITY X-RAYS HVL See last green box on pg 142

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

Interaction with Matter Chapter 9 Interaction with Matter

INTERACTION WITH MATTER X-RAYS AND INTERACTION WITH MATTER

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

Low energy 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

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

Medium energy Scattered x-ray can go many directions not useful 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

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

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

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

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

WHAT IS MASS DENSITY?

Contrast examination Barium Iodine Air

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