xray interactions

Question 1

what are the 2 important interactions for diagnostic imagin

Answer 1

compton scatter and photoelectric effect

Question 2

what happens in coherent scatter interactions

Answer 2

photon changes directions resulting in film fog
no change in energy

interaction between photon and outer shell electron
photon is scattered and is of lower energy than incident photon
a secondary electron is released

Question 3

what is the probability for a coherent scatter

Answer 3

1/E

Question 4

what happens in photoelectric effect interactions

Answer 4

photons interact with inner shell electrons liberating the electron causing a vacancy that is filled via an outer shell electron
when the vacancy is filled there is an energy release

Question 5

what is the probability of the photoelectric effect

Answer 5

(1/E)^3

also Z^3 ( proportional to atomic number)

Question 6

what happens during pair production interactions

Answer 6

xray interacts with electric field of nucleus and is then absorbed and produces positron and electron
an annihilation photon is produced by their interaction

Question 7

what occurs during phtodisintegration interactions?

Answer 7

xrays absorbed directly into nucleus producing a nuclear fragment

Question 8

what energies do the 5 interactions occur at typically

Answer 8

Coherent - >1keV
compton -kV energy range
PE around 100kV
PP - >1.02Me
photodis - >10 MeV

Question 9

which interaction i s more likely to occur with high atomic number materials

Answer 9

photoelectric - Z^3

Question 10

which interaction causes fog on the kV image

Answer 10

coherent

Question 11

which interaction causes a significant amount of backscatter

Answer 11

compton

Question 12

what are the 3 posibilities that can occur when a kV photon reaches the patient

Answer 12

absorbed - photoelectric effect
scattered - compton
continue through to the image receptor

Question 13

describe differential absoption

Answer 13

the differences in the photon absorption of different tissues due to their respective atomic numbers
results in image contrast and the formation of the image

Question 14

differential absorption increases as ____ is reduced

Answer 14

kvp

Question 15

if there is little difference in atomic number of tissues while high kvp or low kvp allow for the maximum differential absorption

Answer 15

low

imagine if they were high, all the photons would pass through almost equally

Question 16

reducing kvp allows for max differential absoption resulting in better _____ in your image.
to compensate for lower kVp you must ______ ___

Answer 16

contrast

increase mA

Question 17

define optical density

Answer 17

radiographic density

degree of blackening of the film