Factors controlling intensity

Question 1

What is intensity?

Answer 1

total amount of energy in x-ray beam

Question 2

How do you determine x-ray intensity?

Answer 2

quantity x quality

Question 3

What is the quantity & what is it related to?

Answer 3

number of photons in a beam
- tube current & exposure time (mAs)

Question 4

What is the quality & what is it related to?

Answer 4

average energy of the x-ray beam
- tube voltage (kvp)

Question 5

T/F the x-ray beam is heterogenous?

Answer 5

true: most x-rays are not the maximum energy

Question 6

As tube voltage increases:

Answer 6

• # photons increases (quantity)
• mean energy increases (quality)
• max energy increases

Question 7

As exposure time increases:

Answer 7

• # photons increases (quantity)
• mean energy unchanged
• max energy unchanged

Question 8

As tube current increases:

Answer 8

• # photons increases (quantity)
• mean energy unchanged
• max energy unchanged

Question 9

What is the purpose of filtration?

Answer 9

selectively removes long wavelength/low energy x-rays

Question 10

As filtration increases:

Answer 10

• # photons decreases (quantity)
• mean energy increases (quality)
• max energy unchanged

Question 11

How does collimation affect intensity?

Answer 11

• # photons decreases (quantity)
• mean energy unchanged
• max energy unchanged

Question 12

How to calculate total filtration?

Answer 12

inherent (glass envelope, immersion oil, metal housing, tube window) + added (aluminum disks)

Question 13

As the source to receptor distance increases:

Answer 13

• # photons decreases (quantity)
• mean energy unchanged
• max energy unchanged

Question 14

If the distance to receptor is doubled what will the new intensity be?

Answer 14

1/4

Question 15

What factors affect density ?

Answer 15

time, mA, distance (quantity)
– things that affect the # of x-rays reaching receptor

Question 16

What factors affect contrast?

Answer 16

kVp, filtration (quality)
– things that affect the energy of the x-rays reaching the receptor

Question 17

Higher density images will be lighter or darker & why?

Answer 17

darker because more x-rays reach receptor

Question 18

If exposure time has been doubled and you want to maintain the same density, what can you do?

Answer 18

half the current (mA)

Question 19

What primarily controls the contrast?

Answer 19

voltage

Question 20

Low contrast has short or long gray scale? Why?

Answer 20

long gray scale
– high penetration, high kvp (short-wavelengths)

Question 21

High contrast has short or long gray scale? Why?

Answer 21

short gray scale
– less penetrating (long-wavelengths)

Question 22

Which type of scale/contrast has greater density differences between adjacent areas?

Answer 22

high contrast / short gray scale

Question 23

Which type of scale/contrast has more subtle differences between adjacent areas?

Answer 23

low contrast / long gray scale

Question 24

How does kVp affect contrast?

Answer 24

• high kvp = high contrast
• low kvp = low contrast