Density

Question 1

For selection of an optimal radiographic technique, three groups of factors must be considered

Answer 1

• image quality factors ex density, contrast
• exposure technique factors ex kvp, mAs, SID
• patient factors ex pathology

Question 2

Visibility is achieved with the balance of

Answer 2

• radiographic density

- radiographic contrast

Question 3

Radiographic density

Answer 3

• the amount of overall BLACKNESS produced on the image after processing
• must achieve balance
• must have sufficient density (allows us to visualize the structures, excess or insufficient density results in poor visualization of anatomy)

Question 4

What are the factors that alter radiographic density of images (aka prime exposure factors)

Answer 4

• kVp
• exposure time
• mA
• SID

Question 5

What does it mean when an image is said to be too dark?

Answer 5

• has a high OD
• caused by overexposure
• more information

Question 6

What does it mean when an image is said to be too light?

Answer 6

• has a low OD
• caused by underexposure
• less information

Question 7

OD can be controlled by two major factors

Answer 7

• mAs
• SID
• direct relationship between mAs and OID

Question 8

MAs and exposure

Answer 8

• mAs is primary factor used for density
• determines the number of x-rays produced (quantity)
• direct relationship
• double the mAs=double the exposure
  
  • provided nothing else changes
  • also generally doubles the density

Question 9

Reciprocity law

Answer 9

• the density produced on a radiograph remains the same for any combination of mA and exposure times as long as the value of the mAs is the same
  
  • as long as the resultant mAs is the same, regardless of the mA and time combination used, the OD produced on the image will be the same
• failure of law occurs with: extremely short exposures and extremely long exposures

Question 10

When do we use the reciprocity law?

Answer 10

• motion
• focal spot size
• breathing technique

Question 11

MAs and density

Answer 11

• for us to notice a visible change in radiographic density
  
  • mAs needs to be changed by at least 25-30%
• what if the mAs is changed by 10%?
  
  • the change will not be visible to us
• the general rule of thumb for mAs changes is to make adjustments in doubles or halves

Question 12

What happens when mAs is decreased?

Answer 12

Radiographic density is decreased

Question 13

What happens when mAs is increased?

Answer 13

Radiographic density is increased

Question 14

True or false: mAs controls density; directly proportional

Answer 14

TRUE!!

Question 15

What role does kVp play in optical density?

Answer 15

• affects the intensity of the beam
• controls energy (strength) with which the electrons hit the target (anode)
• major player in quality (some effect on x-ray quantity)
• primary controller of x-ray beam quality and controls RADIOGRAPHIC CONTRAST
• what is contrast? Shades of grey on the image

Question 16

Contrast

Answer 16

• function: to make anatomy more visible
• the difference in OD between the adjacent structures, or the variation of OD on an image
• without it, would not be able to discern structural borders
• is a result of the x-ray beam being attenuated differently as it passes through the tissues of the body

Question 17

Kvp and density

Answer 17

• has an effect on density because it ALTERS PENETRABILITY OF THE BEAM (this also affects the amount of radiation that reaches the IR)
• if the kVp is decreased, less radiation reaches the IR, resulting in: decreased OD (image will be lighter)
• if the kVp is increased, more radiation reaches the IR, resulting in: increased OD

Question 18

15% rule

Answer 18

• increasing the kVp by 15% will have the equivalent effect on radiographic density, as doubling the mAs
• this rule can be applied for maintaining or adjusting density

Question 19

KVp vs mAs

Answer 19

• so if both affect radiographic density, how do I decide what to adjust?
• mAs THE SIMPLEST ADJUSTMENT TO MAKE, as it has a direct relationship with density
• when do we adjust kVp?
• when we want to change the contrast of the image
• when we want to control motion (as kVp is increased, mAs is decreased, meaning shorter exposure times can be achieved)

Question 20

The density of a radiographic image can be defined as?

Answer 20

-the amount of overall blackness produced on the image after processing

Question 21

What type of property is density?

Answer 21

• geometric

- photographic

Question 22

What range of OD can be detected by human vision?

Answer 22

-0.25-2.50 OD

Question 23

What are prime factors?

Answer 23

• kVp
• exposure time
• mA
• SID

Question 24

If you had to choose between an image with too much or too little density you would choose?

Answer 24

• an image with too much density

Question 25

How is visibility achieved?

Answer 25

-with the balance of radiographic density and radiographic contrast

Question 26

What type of relationship does mA and time have with radiographic density?

Answer 26

-directly proportional

Question 27

If all other factors were left unchanged, and the exposure time was decreased from 0.1 sec to 0.05s, how will the radiographic density on the image be affected?

Answer 27

-the density has been halved

Question 28

KVp primarily controls

Answer 28

Contrast

Question 29

True or false: The number of electrons in the thermionic emission cloud is controlled by kVp

Answer 29

FALSE

Question 30

X-rays with more penetrating power have a ____ wavelength than weaker x-rays

Answer 30

Shorter!

Question 31

When kVp is increased

Answer 31

- the # of x-rays transmitted is increased | - compton scattering is increased

Question 32

What is the relationship between dose and distance?

Answer 32

- if we increase one we have to decrease the other | - inversely proportional

Question 33

Does focal spot size influence the density of an image?

Answer 33

No!

Question 34

What is another name for the density maintenance formula?

Answer 34

Direct square law

Question 35

What is the relationship between distance and density maintenance?

Answer 35

⬆️ distance, ⬇️ density | ⬇️ SID (distance), ⬆️ density

Question 36

How can OID affect radiographic density?

Answer 36

⬆️ OID,results in ⬇️radiograophic density

Question 37

A ______pathology will increase the radiopacity of tissue

Answer 37

Constructive!

Question 38

A _____ pathology will increase the radiolucency of tissue

Answer 38

Destructive

Question 39

When you ____ the kVp, you ____ the number of interactions

Answer 39

-increase, decrease

Question 40

Why is there a difference in intensity of the x-ray beam when the SID is changed? How does this affect radiographic density?

Answer 40

-with increased SID, get a change in intensity. Same # of photons cover a larger area, so they become less intense