Ch 15 & Tube/Target Interactions

Question 1

What factors contribute to Compton scatter

Answer 1

KVp

Volume of irradiated material (part size)

Question 2

What is occupational dose

Answer 2

Compton scatter

Question 3

What does increased kVp do to pt interactions

Answer 3

Less photoelectric absorption
More scatter
Less dose

As long as it goes with decreased MAs

Question 4

How does increased kVp effect image quality

Answer 4

Lower amount of contrast

Question 5

What does decreased kVp do to pt interaction

Answer 5

More photoelectric absorption
More dose
Less scatter

Question 6

How does decreased kVp effect Pt dose

Answer 6

Increased photoelectric absorption meaning Increased dose

Question 7

Decreased kVp effect on image quality

Answer 7

Higher image contrast

Question 8

Increased field size increases the volume of tissue irradiated, what also does this increase

Answer 8

Scatter

Question 9

Decreased field size decrease beam quantity which also

Answer 9

Decreases scatter

Decreases amount of remnant radiation hitting the receptor

Question 10

What is quantum mottle

Answer 10

IR does not receive the correct amount of exposure & causes a greying/grainy effect

Question 11

What do you increase if you decrease the field size to maintain image quality

Answer 11

Mas

More photons make the image look less grainy

Question 12

Is barium/contrast dense or not dense

Answer 12

Dense

Question 13

Atomic number 74

Answer 13

Tungsten

Question 14

Atomic number 56

Answer 14

Barium

Question 15

Atomic number 20

Answer 15

Bone

Question 16

What does beam restriction do for the pt and workers

Answer 16

Decrease scatter
Increase detail
Decrease dose
Decrease scale of contrast

Question 17

What are the types of beam restrictors

Answer 17

Collimator
Aperture diaphragm
Cones
Cylinders

Question 18

What’s the most common beam restrictor

Answer 18

Collimator

Question 19

How many sets of shutters do the Collimator have

Answer 19

Two

Question 20

What type of collimation does the Collimator allow

Answer 20

Rectilinear collimation

Question 21

What do the bottom shutters reduce

Answer 21

Penumbra

Question 22

What is penumbra

Answer 22

Geometric unsharpness

Question 23

What does the upper shutters reduce

Answer 23

Off focus radiation

Question 24

What is off focus radiation

Answer 24

Image shadows - ghosting

Question 25

What percent of accuracy does the light field need to be within

Answer 25

+/- 2% of SID

Question 26

What is PBL

Answer 26

Positive beam limitation

Question 27

What does PBL do

Answer 27

Automatically collimate the light field to the size of the IR - you can reduce the light field still but not increase it bigger than IR

Question 28

What does scatter create on the IR

Answer 28

Fog

Question 29

What does a grid do

Answer 29

Cleans up scatter - soft photons

Question 30

How are the shutters in the Collimator positioned

Answer 30

At right angles of each other. That shutter in opposing directions

Question 31

Example of Lead blocker

Answer 31

Shield

Question 32

When xray photons interact with matter and lose energy through those interactions, it is called

Answer 32

Attenuation

Question 33

Scattered photons that are deflected back towards the X-ray source is called

Answer 33

Back scatter

Question 34

What can coherent scatter also be called

Answer 34

Classical scatter Thompson scatter Unmodified scatter

Question 35

What is coherent scatter

Answer 35

Very low energy xray (10kev or lower) - non diagnostic The atom is excited and releases energy by producing a secondary photon equal to the incident photon - just moving in a different direction.

Question 36

What is photoelectric absorption

Answer 36

Patient dose Xray photon interacts with inner shell electron & ejects it, which gets absorbed by the pt. The atom is now ionized & a photoelectron is produced.

Question 37

What is Compton scattering

Answer 37

Occupational dose - AKA Compton effect Incident photon interacts & removes a loosely bound outer electron, loses 1/3 its energy & proceeds in a new direction as a scattered photon. It can continue to interact with more matter or exit the body

Question 38

What is pair production

Answer 38

Does not occur in diagnostic xray Very high energy photons (1.02 MeV or higher) gets close to the nucleus causing it to lose all of its energy. The result is production of a negatron & positron

Question 39

What is photo-disintegration

Answer 39

Does not occur in diagnostic xray Extremely high energy photons (10 MeV or higher) Photon strikes the nucleus & energy is absorbed, the nucleus gets excited & emits a nuclear particle

Question 40

Will increased kVp increase scatter or decrease scatter

Answer 40

Increase - more power behind the photons, the more chance it will act as a pin ball & go in all directions

Question 41

When will photoelectric absorption happen

Answer 41

When lower kVp is used When contrast agents are used

Question 42

Low kVp does what to contrast

Answer 42

High contrast

Question 43

High kVp does what to contrast

Answer 43

Decreased contrast