Ch. 8 X-ray emission

Question 1

What is the intensity of the x-ray beam of an x-ray imaging system measured in in air?

Answer 1

mGy(subscript a) formerly milliroentgen

Question 2

What is mGy (air) called?

Answer 2

x-ray quantity

Question 3

x-ray quantity and radiation exposure are both measured in…

Answer 3

mGy (air) or mR

Question 4

mGy measures what in the air?

Answer 4

the number of ion pairs produced in the air by a quantity of x-rays.

Question 5

X-ray quantity is the number of…

Answer 5

x-rays in the useful beam

Question 6

Most general purpose radiographic tubes, when operated at 70 kVp produce x-ray intensities of about…

Answer 6

50 microgray/mAs or 5 mR/mAs at a 100cm SID

Question 7

x-ray quantity is directly proportional to…

Answer 7

mAs

Question 8

formula for relationship of mAs to quantity

Answer 8

I(1)/I(2) = mAs(1)/mAs(2)

Question 9

x-ray quantity is proportional to the square of the ratio of…

Answer 9

kVp

Question 10

formula for relationship of kVp to quantity..

Answer 10

I(1)/I(2) = (kVp(1)/kVp(2))^2

Question 11

to maintain constant exposure of the IR, kVp should increase by ___ and mAs should…

Answer 11

15%, decrease by 50%

Question 12

DESCRIBE inverse square law.

Answer 12

x-ray intensity varies inversely with the square of the distance from the x-ray tube target

Question 13

Formula for inverse square law?

Answer 13

I(1)/I(2) = (d (2)/d (1))^2

Question 14

To maintain constant exposure when SID is increased, mAs should be…

Answer 14

increased by SID^2

Question 15

What is the formula for the square law?

Answer 15

mAs (1)/mAs (2) = SID(1)^2/SID(2)^2

Question 16

DESCRIBE the square law

Answer 16

When SID is increased, mAs must be increased by SID^2 to maintain constant exposure to the IR

Question 17

How much filtration is positioned in the useful beam in a metal filter?

Answer 17

1-5 mm of Al

Question 18

Adding filtration to the useful beam reduces…

Answer 18

patient dose

Question 19

As the energy of an x-ray beam is increased, the penetrability is…

Answer 19

also increased

Question 20

What does penetrability refer to?

Answer 20

the ability of x-rays to penetrate deeper in tissue

Question 21

Penetrability of a beam is also called…

Answer 21

x-ray quality

Question 22

What do not affect radiation quality?

Answer 22

Distance and mAs

Question 23

Attenuation is…

Answer 23

the reduction in x-ray intensity that results from absorption and scattering

Question 24

How is the quality of x-rays measured?

Answer 24

by the HVL.

Question 25

What is the range of the HVL in a diagnostic beam?

Answer 25

3-5 mm Al or 3-6 cm of soft tissue

Question 26

The HVL is the…

Answer 26

thickness of absorbing material necessary to reduce the x-ray intensity to half of its original value.

Question 27

X-ray beam quality can be identified by kVp or filtration, but what is most appropriate?

Answer 27

HVL

Question 28

What can increase x-ray quality?

Answer 28

kVp and Filtration

Question 29

What can increase x-ray quantity?

Answer 29

mAs & kVp

Question 30

What can reduce x-ray quantity?

Answer 30

distance and filtration

Question 31

What has no affect at all on x-ray quality?

Answer 31

mAs & Distance

Question 32

What happens to beam quality and the HVL if kVp is increased?

Answer 32

quality is increased

Question 33

What are the classifications of filtration?

Answer 33

added, inherent, compensating

Question 34

How much filtration is in the inherent classification?

Answer 34

0.5 mm of equivalent Al

Question 35

What is the bow tie filter?

Answer 35

a filter used with CT to compensate the shape of the head or body