Prime Factors

Question 1

What are the three principal factors that affect X-ray quality and quantity?

Answer 1

1. Milliamperage per second (mAs)
2. Kilovoltage (kVp)
3. Distance

Question 2

What does the term ‘Quantity’ refer to in X-ray imaging?

Answer 2

The measure of the number of x-ray photons in the useful beam

Also known as output, intensity, or exposure, measured in roentgen (R).

Question 3

What is the prime controller of X-ray quantity?

Answer 3

Milliamperage per second (mAs)

It is also affected by kilovoltage (kVp), distance, and filtration.

Question 4

What does ‘Quality’ measure in X-ray imaging?

Answer 4

The penetrating ability of the x-ray beam

It is numerically represented by the Half Value Layer (HVL).

Question 5

What is the relationship between mA and exposure time in X-ray imaging?

Answer 5

Both mA and exposure time are directly proportional to the number of electrons crossing the tube and the number of x-ray photons created.

Question 6

How is mAs calculated?

Answer 6

mAs = mA x s

Where mA is tube current and s is exposure time.

Question 7

What is the Exposure Index (EI)?

Answer 7

A numeric exposure value used to assess image receptor (IR) exposure

It indicates the amount of exposure received but does not indicate patient dose.

Question 8

What happens if the EI value falls outside the specified range?

Answer 8

It indicates an over or under-exposed image.

Question 9

What is the effect of increasing kVp on the number of x-ray photons?

Answer 9

A 15% increase in kVp doubles the number of photons

Doubling kVp increases the number of photons about four times.

Question 10

How does kVp affect image contrast?

Answer 10

Higher kVp results in lower contrast, while lower kVp results in higher contrast.

Question 11

What is the 15% Rule in X-ray imaging?

Answer 11

An increase or decrease in kVp by 15% will double or halve the exposure.

Question 12

What is the Inverse Square Law in the context of X-ray distance?

Answer 12

Doubling the distance increases the area by 4 times, decreasing the intensity by ¼.

Question 13

What is the Direct Square Law used for?

Answer 13

To compensate for IR exposure changes when the distance changes.

Question 14

How does increasing distance affect X-ray exposure?

Answer 14

Increasing distance causes a decrease in exposure.

Question 15

What should the radiographer consider when setting kVp?

Answer 15

The desired contrast for the image.

Question 16

What is the responsibility of the radiographer regarding mAs?

Answer 16

To adjust mAs to provide the appropriate total exposure to the receptor.

Question 17

True or False: Higher kVp and lower mAs generally reduce patient dose.

Answer 17

True

This reduction is at the expense of contrast.

Question 18

Fill in the blank: The measure of the number of X-ray photons in the useful beam is known as _______.

Answer 18

Quantity

Question 19

Fill in the blank: The prime controller of X-ray quality is _______.

Answer 19

Kilovoltage (kVp)