Physics: Radiation Quantities And Units 1

Front 1

What are several factors that make it difficult to determine how much radiation a patient has recieved

Back 1

include the many quantities that can be used to express the amount of radiation, the different units that are used, and the generally uneven distribution of the radiation within the patients body.

Front 2

What are the 2 main ways radiation quantities can be expressed

Back 2

Concentration and total

Front 3

What is being looked at when units of concentration are being used

Back 3

photon fluence
energgy fluence
exposure
dose
dose equivalent

Front 4

What is being looked at when the total radiation units are being used

Back 4

total photons
total energy
integral exposure
intregral dose
effective dose equivalent

Front 5

What is concentration of radiation mostly concerned with

Back 5

the concentration of radiation at some point (such as exposure) , or to a specific tissue or organ ( absorbed dose)

Front 6

What is total radiation concerned with

Back 6

total radiation delivered to the body

Front 7

What are the two types of Units of measurements of quantities of radiation

Back 7

conventional
SI (metric)

Front 8

What are the quanities of radiation measured

Back 8

concentration
total radiation

Front 9

What are the units

Back 9

conventional
SI

Front 10

What are the conventional units of radiation measurement

Back 10

the three R's
roentgen
rad
rem
and coloumbs

Front 11

What units make more sense

Back 11

the conventional (old will often have nice rounded numbers) the SI units where made for the sake of having one unifying system of measurment

Hint 11

The SI units are
C/kg (=roetgens)
sieverts (rem)
greys (rads)

Front 12

Why do the conventional units sometimes still get used today

Back 12

However, because of their practicality and familiarity, some of the conventional units, especially the roentgen, will continue to be used by many.

Front 13

How is all forms of electromagnetic radiation packaged

Back 13

into small units of energy called photons

Front 14

What is the physical differentce between different types of radiation

Back 14

he physical difference between the different types of radiation, like light and x-rays is the amount of energy packed in each photon

Front 15

What are 2 useful ways of expressing the radiation delivered to the body

Back 15

total number or the concentration of the photons

Front 16

graphic representation of how much energy is contained in sunlight and x ray radiation

Back 16

note how the total amount of photons or concentration is not related to the energy

Front 17

Why is expressing the amount of radiation delivered to an object in terms of either the total number or the concentration of photon

Back 17

There are several reasons. One is that the number of photons in a typical x-ray beam is such a large number, like in the billions or more, that it is not a practical quantity to work with

Front 18

Do we have a practical instrument for counting large quanitites of photons in an X-ray bem

Back 18

no

Front 19

What is a good way to think of radiation

Back 19

a shower of photons

Front 20

What are 2 situations in medicine where the number of photons is important

Back 20

Total photon (measure of radioactivity in curies or becquerels
Photon Concentration (fluence in photons/unit area)

Front 21

Where do photon fluence and total photons fit in the quantities chart

Back 21

Front 22

What is total photons

Back 22

a measure of radioactivity (curies or becquerels)

Front 23

How is the total photons measured

Back 23

One method used to measure the radioactivity of a sample is to count the photons that are emitted. Then, with proper calibration factors, the counts per minute (CPM) can be converted into units of radioactivity, curies or becquerels.

Front 24

What does photon concentration (fluence) determine

Back 24

a factor of image quality

Front 25

What is critical in medical imaging

Back 25

the concentration of photons absorbed in the image forming process is a very critical factor (fluence= photons/unit area)

Front 26

Why is the quantity of radiation absorbed so important

Back 26

this is the principle factor that determines the amount of visual noise in the image. That is the so-called quantum (photon) noise

Front 27

In projection imaging (radiography, fluoroscopy, gamma camera) the critical quantity is the concentration (photons/unit area) absorbed by the image receptor that determines the noise leve

Back 27

yes

Front 28

Is energy commonly used for expressing the amount of radiation delivered to the body

Back 28

yes, rad or Gy (absorbed dose)

Front 29

What is the concentration of energy absorbed in tissue

Back 29

the concentration of energy absorbed in tissue is the quantity, Absorbed Dose (rad or Gy)

Front 30

What is the total energy absorbed in a body

Back 30

the total energy absorbed in a body is the Integral Dose (Joule in SI and conventional unit is the gram-rad)

Front 31

What are 2 quantities we have talked about

Back 31

Photons (total [curies or becquerels] and concentration[photon per unit area])
Energy (absorbed dose [Gy or Rad] and intergral dose [Joule in SI and conventional unit is the gram-rad])

Front 32

Is Exposure a 3rd radiation quantity

Back 32

yes

Front 33

What is exposure

Back 33

Exposure is a radiation quantity that expresses the concentration of radiation delivered to a specific point, such as the surface of the human body

Front 34

d

Back 34

d

Front 35

Surface Exposure

Back 35

this is expressed as either surface intergral exposure or exposure

Front 36

Surface Exposure

Back 36

this is expressed as either surface intergral exposure or exposure

Front 37

Where is Exposure and Surface intergral exposure located in the quantities chart

Back 37

Front 38

What are the units of exposure

Back 38

roentgens

Front 39

What are the units of surface integral exposure

Back 39

R-cm^3

Front 40

Is exposure a measure of concentration

Back 40

yes

Front 41

Is surface intergral exposure a measure of total dose

Back 41

yes

Front 42

What are the 2 units for expressing exposure

Back 42

roentgen and SI coulomb/kg of air (C/kg of air)

Front 43

What is the most common quantitiy used to express the amount of radiation at a given point

Back 43

exposure

Front 44

What is the more common term for photon concentration

Back 44

photon fluence


MOVE

Front 45

How is total photons related to photon concentration or fluence

Back 45

This quantity depends on the size of the exposed area and the radiation concentration. If the radiation is uniformly distributed over the exposed area, the total number of photons entering the patient can be found by multiplying the concentration (fluence) by the exposed area

Front 46

What are the units of exposure

Back 46

R (conventional)
Coloumbs/kg (SI)

Front 47

What is the conversion for roentgens to C/kg

Back 47

1 R = 2.58 x 10-4 C/kg

Front 48

What is the conversion factor for C/kg to R

Back 48

1 C/kg = 3876 R

Front 49

Exposure is the quantity most commonly used to express the amount of radiation delivered to a point.

Back 49

yes

Front 50

Why is exposure commonly used

Back 50

The reason exposure is such a widely used radiation quantity is that it can be readily measured (total photons and photon fluence are very difficult to measure and that is one reason why that is not used)