Radiation Units & Quantities (CTBC 21)

Question 1

2 means of measuring x-rays

Answer 1

Radiation in Air
Radiation in Tissue

Question 2

Exposure

Answer 2

Number of ionizations created in air

Question 3

Units of Exposure

Answer 3

Coulombs per kilogram (C/kg)

Question 4

6.242x10^18 ionizations equals

Answer 4

1 coulomb

Question 5

Traditional units of radiation measurement

Answer 5

Roentgens (R)
(more common in practice)

Question 6

2.58 x 10^-4 C/kg

Answer 6

1 Roentgen

Question 7

Typically the exposure in air created by CT is significantly less than…

Answer 7

1C/kg or 1R
(1 C/kg ~ 3876 R)

Question 8

(air) KERMA

Answer 8

Kinetic Energy Released per unit MAss
(Alternative to measuring exposure)

Question 9

Air kerma quantifies radiation by measuring

Answer 9

Energy of ionizations

Question 10

Ionizations

Answer 10

Liberated electrons

Question 11

Air kerma measures _____ of ionizations; Exposure measures _______ of ionizations

Answer 11

energy
number

Question 12

Air Kerma Units

Answer 12

Gy
mGy

Question 13

Both _______ and _______ can be used to measure radiation produced by CT x-ray tube, scatter radiation produced during CT procedure, scatter radiation escaping CT scan room

Answer 13

Exposure
Air kerma

Question 14

Measuring the radiation produced by a CT x-ray tube is readily done with

Answer 14

Exposure or Air Kerma

Question 15

Measuring the scatter radiation produced during a CT procedure is readily achieved using

Answer 15

Exposure or Air Kerma

Question 16

Measuring the scatter radiation escaping the CT scan room is readily achieved using

Answer 16

Exposure or Air Kerma

Question 17

Increasing mA _______exposure and air kerma

Answer 17

Increases

Question 18

Increasing kVp _______ exposure and air kerma

Answer 18

Increases

Question 19

The most basic way to quantify the amount of radiation energy absorbed by the body

Answer 19

Absorbed dose (D)

Question 20

Units for absorbed dose (D)

Answer 20

Gy/mGy
(Rad/mRad)

Question 21

1 J/kg =

Answer 21

1Gy

Question 22

An extension of absorbed dose measured in Sv/mSv (rem/mrem)

Answer 22

Equivalent dose (EqD)
(EqD = D x Wr)

Question 23

Wr (W-subR)

Answer 23

Radiation weighting factor: used to define difference in biological damage between different radiation types

Question 24

Wr (W-subR) for x-rays

Answer 24

1

Question 25

Wr (W-subR) for gamma rays

Answer 25

1

Question 26

Wr (W-subR) for beta particles

Answer 26

1

Question 27

Wr (W-subR) for protons

Answer 27

5

Question 28

Wr (W-subR) for slow neutrons

Answer 28

5

Question 29

Wr (W-subR) for fast neutrons

Answer 29

10

Question 30

Wr (W-subR) for alpha paticles

Answer 30

20

Question 31

Because CT utilizes x-rays, the EqD is always equal to _______ x D

Answer 31

EqD = (1)D

Question 32

In CT the difference between EqD and D is

Answer 32

Units: Sv vs Gy

Question 33

EfD (equation)

Answer 33

Effective Dose EfD = (D)(W-subR)(W-subT)

Question 34

Purpose of EfD

Answer 34

Accounts for specific radiosensitivities of different tissue types

Question 35

Wt (W-subT) for bone marrow

Answer 35

0.12

Question 36

Wt (W-subT) for breasts

Answer 36

0.12

Question 37

Wt (W-subT) for lungs

Answer 37

0.12

Question 38

Wt (W-subT) for colon

Answer 38

0.12

Question 39

Wt (W-subT) for stomach

Answer 39

0.12

Question 40

Wt (W-subT) for gonads

Answer 40

0.08

Question 41

Wt (W-subT) for liver

Answer 41

0.04

Question 42

Wt (W-subT) for thyroid

Answer 42

0.04

Question 43

Wt (W-subT) for brain

Answer 43

0.01

Question 44

Tissue weighting factors (Wt (W-subT)) represents the *comparative* risk of

Answer 44

Developing radiation-induced cancer

Question 45

Describes the biological effect of a given dose of radiation

Answer 45

Equivalent dose (EqD) (EqD = D x Wr)