Radiography Calculations

Question 1

what is the relation between kV and electrons?

Answer 1

the higher the kV, the faster the electrons will travel towards the anode

Question 2

what happens to the wavelength and colour of the image with a high kV?

Answer 2

• short wavelength
• darker image

Question 3

what happens to the wavelength and colour of the image with a low kV?

Answer 3

• lower wavelength
• paler image

Question 4

what is the relation between mA and the colour of the image?

Answer 4

a high mA results in more x-rays and therefore a blacker image

Question 5

what is the relation between time and the number of x-rays produced?

Answer 5

the longer the time, the more x-rays produced

Question 6

what is a grid?

Answer 6

a flat plate which is placed between the patient and the cassette

Question 7

what does a grid consist of?

Answer 7

a series of thin, lead strips alternating with strips of a material that allows x-rays to pass through

Question 8

what is a parallel grid?

Answer 8

stationary grid with alternating vertical strips of lead and radiolucent material

Question 9

what is a focused grid?

Answer 9

stationary grid with central alternating vertical strips and gradually sloping strips of lead and radiolucent material

Question 10

what is a pseudo focused grid?

Answer 10

stationary grid with vertical slats that become shorter on the edges

Question 11

what is a crossed grid?

Answer 11

stationary grid with vertical and horizontal strips of a radiolucent material

Question 12

what is a pro and con of using a grid during x-rays?

Answer 12

pro - reduces scatter radiation
con - expensive to buy

Question 13

if an x-ray was overexposed, what colour would it be?

Answer 13

black

Question 14

if an x-ray was underexposed, what colour would it be?

Answer 14

white

Question 15

what is density?

Answer 15

The degree of blackening of an x-ray

Question 16

what is contrast?

Answer 16

the difference between adjacent areas on a radiographic image

Question 17

what is the equation for mAs?

Answer 17

mA x S = mAs

Question 18

what is the 10kV rule?

Answer 18

• increasing the kV by 10 allows the mAs to be halved
• decreasing the kV by 10 means doubling the mAs

Question 19

what is the grid factor rule?

Answer 19

old exposure x grid factor = new exposure

Question 20

why do we have exposure charts?

Answer 20

• to provide consistent methods of choosing the proper exposure
• health and safety

Question 21

what is focal film distance?

Answer 21

the focal distance between the x-ray head and film is known as FFD

Question 22

what does changing the focal film distance have an effect on?

Answer 22

the intensity

Question 23

what is the the inverse square law (FFD Rule)?

Answer 23

doubling the distance, quarter the effect
halving the distance, x4