Radiation Physics

Question 1

X-ray definition

Answer 1

Form of radiation- transfer of energy or energetic particles from one place to another
Energy released can cause electrons from an atom to leave, hence ionizing the atom = ionizing radiation
Part of electromagnetic spectrum
Gamma rays are another example of ionizing radiation

Question 2

X-rays properties

Answer 2

Travels at speed of light
Cannot be refracted or reflected like light
No electrical charge and remain unaffected by magnetic or electrical fields
Travel in a straight line
Can penetrate matter to some degree
Can cause florescence 
Can interact with photogenic emulsion
Can cause ionization
Can cause ionization 
Cannot be felt
Invisible

Question 3

Non-ionizing radiation

Answer 3

Transfer of energy occurs in waves
Microwaves and radio waves do not have enough energy to cause the creation of ions
Long wavelengths and low frequencies

Question 4

Ionizing radiation

Answer 4

Short wavelengths and high frequencies
Sufficient energy can be transferred to living tissue and cause the creation of ions within those tissues
Molecular change
Cellular change
Loss of cell function or abnormal cell function
Genetic or somatic abnormalities: mutations, cataracts and leukemia/cancer, death

Question 5

Hazards of radiation

Answer 5

Cell sensitivity- the most sensitive have high division rate : gonads and embryonic tissue
Damaged sperm and eggs can carry on defects to next gen
1st trimester= embryonic death, congenital abnormalities or growth defects

Question 6

Inverse square law

Answer 6

Double distance away from the primary beam, intensity of the beam should diminish to 1/4th the original intensity

Question 7

Why should you observe radiation saftey

Answer 7

Compliance with the law
Concerned about your health and also that of your employees
You can be sued if employees are sick because of your lack of radiation safety

Question 8

Natural radiation

Answer 8

Terrestrial- earth’s crust

Cosmic- solar

Question 9

Manmade radiation

Answer 9

Air travel
Nuclear fuel
Medical radiation

Question 10

Dose limit- public exposure

Answer 10

1 mSv or 0.1 rem per year

Question 11

Dose limit- Occupation exposure

Answer 11

50 mSv or 5 rem per year

Persons should be at least 18

Question 12

Embryo/fetus exposure

Answer 12

5 mSv for entire gestation

Question 13

How to lower occupational dose

Answer 13

Persons taking radiographs should be aware of the risks, have proper training in positioning and machine operations
Proper care of the protective equipment
ALARA principle

Question 14

ALARA principle

Answer 14

Making reasonable effort to limit exposure to ionizing radiation using time, distance, and shielding
As Low As Reasonably Achievable

Question 15

Time

Answer 15

Minimize number of retakes
Only the correct number of views needed
Sedation or anesthesia
Knowledgable staff
Rotation of staff

Question 16

Distance

Answer 16

As much distance between personnel and primary beam
Remember the inverse square law
use of cassette holders
holding the patients is allowed if done properly and persons are adequately shielded
No body part of the personnel should be in the primary beam

Question 17

Sand bags/socks

Answer 17

Physical restraint can aid in increasing distance from primary beam

Question 18

Shielding

Answer 18

Providing protection from scattered radiation
Increases the radiation dose of personnel
Scattered radiation also negatively impacts the radiographic image
Use of personal shielding: lead or lead equivalent impregnated clothing
lead aprons and gloves- 0.5mm
thyroid shields- 0.25 or 0.5mm
Eye glasses- 0.75 mm
Can also use structural shielding like screens and lead impregnated doors and walls

Question 19

Collimation

Answer 19

Adjustable lead shutters controls the size of the x-ray beam

smaller beam surrounding the area of interest means less scattered radiation production resulting in a shaper image

Question 20

Personal monitoring

Answer 20

Monitor radiation of exposure of employees
Radiation badge is the most common form of personnel monitoring
Rings used if there is much hand holding
Should be analyzed quarterly and keep track
Badge only worn on job and worn on outside near collar

Question 21

Radiation safety

Answer 21

Use of physical restraint
Chemical restraint
no body parts in primary beam
limit number of persons in the room
Collimation
no holding of cassettes
wearing lead apparel

Question 22

X-ray production

Answer 22

Cloud of electrons created when current is applied to a wire filament and electrons released
negatively charges so attracted to positively charges metal structure-anode
Striking of e on metal surface creates energy in form of xrays (1%)/photons and heat (99%- inefficient)
rotating anode helps to dissipate heat
High melting point of tungsten

Question 23

X ray tube housing

Answer 23

The xray tube is surrounded by a metal casing which is lined with lead
The lead contains the xrays so they they can only escape through a small opening

Question 24

Collimator

Answer 24

Controls the size of the xray beam

Question 25

Radiographic table

Answer 25

Image receptor is placed under the table

Grid is placed between the patient and image receptor

Question 26

Grid

Answer 26

Plate made up of alternating strips of lead and aluminum and placed at an angle.
80-160 lines per inch and properly aligned
To absorb scatter radiation, preventing it from reaching the image receptor
Scatter radiation causes fogging of the image and degrades the quality of the image
Patient thickness over 10 cm
Some of the primary beam will also be absorbed by the grid, need to increase mAs at least 2-3 times to compensate for the use of the grid

Question 27

mAs

Answer 27

The number of photons/xrays formed is related to the mA (milliampere) setting on the xray machine
Time setting (seconds) determines how long the electrons are allowed to hit the target or anode
The product od time and mA will determine the number of xrays formed

Question 28

kVp

Answer 28

Kilo voltage potential provides the energy needed to move the electron cloud across the gap between the filament and the target or the anode
increasing the kVp increases the energy of the electrons and also the energy of the resulting xrays or photons
Increasing the energy will increase the penetrating power of the photons
As the E increases the different tissue types will look the same- therefore less difference between soft tissue and bone

Question 29

xray too dark

Answer 29

too high kVp or mAs

Question 30

Underexposed radiograph

Answer 30

Need to increase either the mAs (more xrays reaching the film)
Or need to increase the kVp (increase the energy of the xrays so that more ger through the patient)
double mAs or increase kVp by 15%

Question 31

High contrast image

Answer 31

High mAs and low kVp
x ray have less energy
able to penetrate patient or not
More black/white and less grey

Question 32

Low contrast image

Answer 32

low mAs and high kVp
xrays have more energy
able to penetrate to varying degrees
more greys

Question 33

Image contrast- thorax

Answer 33

Low contrast bc thorax has its own inherent contrast

more greys- high kVp and low mAs

Question 34

image contrast- abdomen

Answer 34

less contrast in abdomen

less greys- high mAs and low kVp

Question 35

Radiopacities

Answer 35

Dark to light

air, fat, water, bone, metal

Question 36

Intensifying screens

Answer 36

convert xrays into visible light
xray film emulsion is more sensitive to visible light than to xrays
xray production is made more efficient by converting the xrays to visible light
screens hae florescent material which light up when struck with xray
Film is pressed between 2 screens in a cassette, thus increasing the chance of getting exposed during a radiographic study
System uses much lower mAs compared with exposing xray film directly by 100 times

Question 37

Benefits of intensifying screens

Answer 37

less xrays needed radiographic film
less radiation exposure for the patient and medical personnel
less stress on the xray tube
less chance of motion artefact
image detail decreases as the thickness of the fluorescent layer increases, the light produced can diffuse and be absorbed before reaching the film

Question 38

Processing xray film

Answer 38

xray film is coated with an emulsion which is comprised of silver halide crystals
When film is exposed to light or xray, elemental silver is deposited onto film surface
Upon chemical development the silver deposited on the surface is black
The unexposed areas of film, the unexposed silver halide is rinsed away during processing leaving those areas white and varying degrees of grey of the image
During this process, many artefacts are produced affecting quality of film