Principles of Image formation and Radiation safety

Question 1

What are x-rays?

Answer 1

A form of electromagnetic radiation

Question 2

What can electromagnetic radiation differ in?

Answer 2

wavelength, energy, frequency

Question 3

Long wavelength creates what level of energy and frequency?

Answer 3

low energy and low frequency

Question 4

How are x-rays able to create an image?

Answer 4

a radiograph is a series of silhouettes where x-rays can penetrate matter, however x-rays will penetrate different types of tissues at different levels

Question 5

List tissues in order of high attenuation to low attenuation.

Answer 5

Metal, Bone, Soft tissue, fat, air

Question 6

Low attenuation is equal to what level of transmitted x-rays and radiographic appearance?

Answer 6

high transmitted X-rays and black radiographic appearance

Question 7

Film is like toast…

Answer 7

the more exposure the darker it gets

Question 8

What is ionization?

Answer 8

when energy is high enough to completely knock electrons out of orbit

Question 9

What is the molecular effects of ionizing radiation?

Answer 9

to produce ions that further result in changes in molecular composition

Question 10

what are the cellular effects of ionizing radiation?

Answer 10

radiation damages all cellular constitutes but some are more harmful then others for example DNA damage

Question 11

What is the main/critical target of ionizing radiation?

Answer 11

DNA

Question 12

What can happen if DNA damage occurs?

Answer 12

It may be repaired or may produce mutations or cell death

Question 13

What is the direct effect of radiation injury?

Answer 13

radiation directly hits the DNA (less likely)

Question 14

What is the indirect effect of radiation injury?

Answer 14

production of free radicals that can diffuse far enough to reach and damage the critical target (DNA, RNA, Proteins)

Question 15

What is the relative susceptibility of cells, tissues, organs, or organisms to the harmful effects of ionizing radiation called?

Answer 15

radiosensitivity

Question 16

What kinds of cells are more radiosensitive?

Answer 16

stem cells (important for pregnant women especially in 1st trimester)

Question 17

what kinds of tissue is more radiosensitive?

Answer 17

• young tissue
• tissue with high metabolic activity (gonads)
• proliferating tissue

Question 18

What are some outcomes of chronic low level radiation injury?

Answer 18

genetic effects
carcinogenesis
effects on growth and development
reduced life span
cataracts

Question 19

What is the guiding principle of radiation safety?

Answer 19

ALARA: As low as reasonably acheivable

Question 20

What three basic principles does ALARA adhere to?

Answer 20

Distance, time, shielding

Question 21

What are some ways you could use minimize the time of exposure to radiation?

Answer 21

minimize holding patients

• use sedation
• positioning devices
• rotate personel

develop good technique chart to minimize retakes

Question 22

What is one of the biggest impacts in minimizing exposure to radiation?

Answer 22

maximize your distance from radiation source

doubling your distance from the source will reduce exposure by 1/4th

Question 23

What else can be done to maximize distance from radiation source?

Answer 23

don’t manually hold portable x-ray machines or cassettes

stand away from X-ray tube as possible when making exposures

Question 24

How can shielding help promote radiation safety?

Answer 24

Using personal protection such as lead aprons, gloves, and thyroid shields
(this will only help protect you from scatter radiation, not the main beam)

Question 25

What is the maximum permissible dose for the general public?

Answer 25

2% of the occupational level

Question 26

What is the MPD of occupational workers?

Answer 26

5,000mrem/yr 18 is minimum age

Question 27

What is the mA selector?

Answer 27

number of x-rays in beam (quantity)

Question 28

What is the focal spot selector?

Answer 28

trade-off between resolution and quantity of radiation

Question 29

What is the timer (msec)?

Answer 29

number of x-rays in beam (quantity)

Question 30

What is the mAs selector

Answer 30

mA x Time | number of x-rays in beam

Question 31

What is the kVp selector

Answer 31

energy of beam (quality) | number of x-rays (quantity)

Question 32

What is the 1st step in the production of x-rays?

Answer 32

(prep) electrons are generated by electrical current through the filament in the cathode, its brought up to a certain temp which makes the filament glow, its so hot the e- go free and surround filament

Question 33

what is the 2nd step in the production of x-rays?

Answer 33

(expose) x-rays are produced when electrons interact with metal in the anode (tungsten) due to a voltage

Question 34

What controls the current to the filament?

Answer 34

mA selector | the more current applied, the hotter the filament, the more x-rays produced

Question 35

What does focal spot size influence?

Answer 35

resolution (sharpness) smaller focal spot sharper image -sometimes you have to give up resolution to see a big body part

Question 36

When would you use the small filament in the cathode?

Answer 36

for low output exposures where high detail is needed

Question 37

What is the large filament used for?

Answer 37

high output exposures

Question 38

What determines the voltage across the X-ray tube and contrast of an image?

Answer 38

kVp selector

Question 39

what is gradual transition with shades of gray?

Answer 39

low contrast

Question 40

what is sharp transition with few shades of gray?

Answer 40

high contrast

Question 41

What is the role of the X-ray tube housing?

Answer 41

metal housing which contains lead to shield x-rays produced in different directions other than the patient

Question 42

what factors increase scatter radiation?

Answer 42

the greater amount of body area exposed to radiation the greater amount of scatter -collimating the beam reduces scatter

Question 43

What how do collimators improve image quality?

Answer 43

by reducing scatter radiation

Question 44

how do collimators work?

Answer 44

they restrict the x-ray beam to a confined region | -located outside tube housing

Question 45

what are the devices used to prevent scatter radiation from reaching the film?

Answer 45

grid

Question 46

how does scatter radiation decrease image quality?

Answer 46

by reducing image contrast

Question 47

How does the grid work?

Answer 47

they are composed of hundreds of alternating lead strips which are angled directly with divergence of the beam scatter radiation will be deflected in other directions preventing them from reaching the film

Question 48

What impacts resolution of digital radiographs?

Answer 48

size of detector elements

Question 49

How is a digital image created?

Answer 49

by assigning a shade of gray or a color to each number in the matrix

Question 50

since images are 2-dimensional what is necessary for image interpretation?

Answer 50

2 views at 90 degree angles

Question 51

What is the degree of attenuation of the x-ray beams dependent upon?

Answer 51

subject density and thickness of the object

Question 52

What phenomenon causes the effect when two objects are superimposed over each other the overlapping portions of the object will appear more opaque?

Answer 52

summation effect

Question 53

Do objects need to be in direct contact to experience the summation effect?

Answer 53

no just superimposed

Question 54

What is it called when two objects of the same subject density are in contact, they will appear to blend together radiographically?

Answer 54

silhouetting effects

Question 55

What is border effacement?

Answer 55

inability to see the margins and edges of structures in contact with the same subject density's (silhouetting effect)

Question 56

What refers to the enlargement of the image relative to the actual size of the object being imaged?

Answer 56

magnification

Question 57

The magnification will be greater when?

Answer 57

the object is further from the film

Question 58

If an object is not in the center of a beam there will be?

Answer 58

distortion