פוטוגרפיה מצגת 10

Front 1

What two types of reactions happen when x-rays hit tissue?

Back 1

Photoelectric reaction and Compton reaction

Front 2

What are the three things that can happen to an electron shot from an xray tube?

Back 2

• penetrate (pass through without particles meeting and without losing energy, e.g. lungs)

• photoelectric effect: completely absorbed (e g. bones)--hits an electron in the inner ring K, ionization--photon with low energy hits electron with high energy, electron absorbs photon's energy and gets knocked out of inner ring, becomes photoelectron. Electron from higher ring fills space.

• Compton effect: photon with high energy hits electron in outer ring, knocks it out (ionized), gives only part of its energy to the electron and then continues to travel in a new direction in the form of scatter radiation, hitting the film and anything else around it

Front 3

What happens in a photoelectric reaction in the body?

Back 3

A photon from the x-ray tube hits an electron in the inner ring of an atom in the body (ionization). The photon needs to have slightly higher energy than the electron. An electron from an outer ring fills the space.

Front 4

What are the conditions of a photoelectric reaction?

Back 4

• photon with low energy (less than 40 KV)
• energy of photon and binding energy of electron must be similar
• higher chance of happening on denser tissue (of body)

Front 5

Energy of photon +

Absorption ?

Penetration ?

Back 5

Energy of photon +Absorption -Penetration +

Front 6

Energy of photon -Absorption ?Penetration ?

Back 6

Energy of photon -Absorption +Penetration - (lungs appear more white...)

Front 7

Density of tissue +

Chance of photoelectric reaction ?

Back 7

Density of tissue +Chance of photoelectric reaction +

Front 8

An organ that can be penetrated does/does not have the photoelectric effect. Why or why not?

Back 8

An organ that can be penetrated does not have the photoelectric effect.

Front 9

Bones do/do not have the photoelectric effect.

Back 9

Bones do have the photoelectric effect. They absorb the radiation, appearing white and providing natural contrast.

Front 10

What can be used to improve the contrast in tissue that does not have the photoelectric effect? How does it work?

Back 10

Contrast agent. It has a high atomic number, so it absorbs the rays instead of being penetrated by them.

Front 11

What are the advantages of the photoelectric effect?

Back 11

• contrast + (organs present with natural contrast--white bones appear white)
• no scatter radiation (all the photons are absorbed)

Front 12

What are the disadvantages of the photoelectric effect?

Back 12

• using high kv (large people or crowded organs) prevent the effect
• tissue absorbs all the radiation (damage to patient)

Front 13

What is the Compton effect?

Back 13

Scatter radiation--photon hits electron in outer ring, knocks it out (ionized), gives only part of its energy to the electron and then continues to travel in a new direction in the form of scatter radiation, hitting the film and anything else around it

Front 14

What increases the chance of the Compton effect?

Back 14

High KV (dependent on energy of x-ray: the photon). NOT dependent on the atomic number of the tissue.

Front 15

True or False: The Compton effect does not depend on the atomic number of the tissue.

Back 15

True

Front 16

Higher mass density, higher chance of _____.

Back 16

An interaction (Compton or photoelectric)--more electrons available to have a reaction

Front 17

Larger field (bigger organ), higher chance of ______.

Back 17

Compton effect (more tissue means higher KV, higher KV means more Compton)

Front 18

Higher KV, higher chance of ___.

Back 18

Compton effect (photons with more energy)

Front 19

When mass density is doubled, the chance for an x-ray interaction is _____.

Back 19

Doubled (twice as many electrons are available)

Front 20

True or false: Even though it's not dense, air can serve as a contrast material.

Back 20

True. Appears black instead of white.

Front 21

Contrast dye raises contrast because it has a high _____.

Back 21

mass density

Front 22

What are the disadvantages of the Compton effect?

Back 22

• hurts image (graininess, fog, חשחרת הסרט, bad contrast)
• the high KV damages tissue and has more radiation
• scatter radiation hurts staff

Front 23

In the Compton effect, a photon hits an electron in the ____ ring.

Back 23

outer

Front 24

In the photoelectric effect, a photon hits an electron in the ____ ring.

Back 24

inner

Front 25

The probability of the _____ effect depends on the energy of the incoming x-ray photon and the composition of the anatomic tissue.

The probability of the _____ effect depends on the energy of the incoming x-ray photon but not the composition of the anatomic tissue.

Back 25

Photoelectric

Compton

Front 26

The _____ effect is dominant in element with high atomic numbers.

Back 26

photoelectric

Front 27

In the ____ effect, the photon must have slightly higher energy than the electron binding energy in the electron of the inner ring.

Back 27

photoelectric

Front 28

Given that most of the elements in the human body have a low atomic number and low binding energy, the _____ effect is dominant in imaging that uses lower levels of radiation.

Back 28

photoelectric (lower levels of radiation, such as in mammograms, mean that the photons have slightly more radiation than the inner ring electrons).

Front 29

The ____ effect is not dependent on the atomic number.

Back 29

Compton

Front 30

The chance of the Compton effect occurring increases with ____ KV.

Back 30

higher

Front 31

The ___ effect decreases the image quality.

Back 31

Compton

Front 32

Scatter radiation spreads from the ____ to the _____.

Back 32

body of the patient, surroundings

Front 33

_____ radiation is secondary radiation.

Back 33

Scatter

Front 34

Primary radiation comes from the ___.

Back 34

x-ray tube

Front 35

Give an example of an x-ray in which the Compton effect would be expected?

Back 35

Stomach x-ray (need higher KV to penetrate more typres of tissues, contrast is hurt so we use dye).

Front 36

What is attenuation?

Back 36

Reduction of the strength of the primary rays as they pass through tissue (by absorption and scatter)

Front 37

Photon energy +

Photoelectric effect ?

Compton effect ?

Back 37

Photon energy +

Photoelectric effect -

Compton effect +

Front 38

Why is scatter radiation the enemy of imaging?

Back 38

Fog, bad contrast, radiation with no useful information

Front 39

What is primary radiation?

Back 39

The radiation that comes from the tube and is absorbed by tissue or penetrates it and gets to the cassette.

Front 40

What is secondary radiation?

Back 40

Scatter radiation that results from a reaction happening in the patient.

Front 41

What is the מנת המעבר?

Back 41

Primary radiation + secondary radiation

Front 42

What is HVL?

Back 42

Half value layer--the thickness necessary (in any material) to reduce the strength of the rays by half

Front 43

Absorption +, attenuation ?

Back 43

+ (photons give up all their energy to the tissue, not much left)