1. Radiation physics and bio part 2

types of x-ray interaction with matter and occurrence %

• coherent 7%

• photoelectric 27%

• compton 57%

• no interaction 9%

start w photon

describe coherent scattering

my own words: photon transfers energy to outer shell electron which scattered that photon in a different direction

important: no change in energy

from lecture: passing of low energy photon near a outer electron causes that electron to vibrate as same frequency and it forms another x-ray photon with same frequency as incident photon

7%

describe photoelectric scattering

photon interacts with inner-shell electron that is then ejected (ionized). all the energy is transferred to the ejected electron and photon no longer exists and characteristic radiation is emitted (low energy and absorbed in pt)

27%

describe clinical significance of photoelectric effect/absorption

Z of bone > Z of soft tissue and this differential makes production of radiographic image possible

describe compton scattering

photon interacts with outer orbital electron, the electron is ejected (ionization) and the photon is deflected as scattered photon with lower energy

describe two important points of compton scattering

• it accounts for 57% of dental x-ray beam interactions

• 30% of scattered photons exit the pts head

describe the three results of differential absorption resulting in radiograph

• radiopaque (white, bone, absorbed)

• radiolucent (black, air, pass through)

• fogged (confuse the image)

define equivalent dose

a measure of comparison of biological effectiveness of different types of radiation

SI unit: Sievert (Sv)

describe three important points of effective dose

• estimates risk by comparing exposure types

• takes into account volume/radio sensitivity of tissue irradiated and biological effectiveness of radiation

• compares x-ray exposures