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Radiology > Principles of Image formation and Radiation safety > Flashcards

Principles of Image formation and Radiation safety Flashcards

1
Q

What are x-rays?

A

A form of electromagnetic radiation

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2
Q

What can electromagnetic radiation differ in?

A

wavelength, energy, frequency

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3
Q

Long wavelength creates what level of energy and frequency?

A

low energy and low frequency

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4
Q

How are x-rays able to create an image?

A

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

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5
Q

List tissues in order of high attenuation to low attenuation.

A

Metal, Bone, Soft tissue, fat, air

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6
Q

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

A

high transmitted X-rays and black radiographic appearance

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7
Q

Film is like toast…

A

the more exposure the darker it gets

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8
Q

What is ionization?

A

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

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9
Q

What is the molecular effects of ionizing radiation?

A

to produce ions that further result in changes in molecular composition

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10
Q

what are the cellular effects of ionizing radiation?

A

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

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11
Q

What is the main/critical target of ionizing radiation?

A

DNA

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12
Q

What can happen if DNA damage occurs?

A

It may be repaired or may produce mutations or cell death

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13
Q

What is the direct effect of radiation injury?

A

radiation directly hits the DNA (less likely)

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14
Q

What is the indirect effect of radiation injury?

A

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

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15
Q

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

A

radiosensitivity

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16
Q

What kinds of cells are more radiosensitive?

A

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

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17
Q

what kinds of tissue is more radiosensitive?

A
  • young tissue
  • tissue with high metabolic activity (gonads)
  • proliferating tissue
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18
Q

What are some outcomes of chronic low level radiation injury?

A 
genetic effects
carcinogenesis
effects on growth and development
reduced life span
cataracts
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19
Q

What is the guiding principle of radiation safety?

A

ALARA: As low as reasonably acheivable

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20
Q

What three basic principles does ALARA adhere to?

A

Distance, time, shielding

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21
Q

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

A

minimize holding patients

  • use sedation
  • positioning devices
  • rotate personel

develop good technique chart to minimize retakes

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22
Q

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

A

maximize your distance from radiation source

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

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23
Q

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

A

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

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

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24
Q

How can shielding help promote radiation safety?

A

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

25
Q

What is the maximum permissible dose for the general public?

A

2% of the occupational level

26
Q

What is the MPD of occupational workers?

A

5,000mrem/yr

18 is minimum age

27
Q

What is the mA selector?

A

number of x-rays in beam (quantity)

28
Q

What is the focal spot selector?

A

trade-off between resolution and quantity of radiation

29
Q

What is the timer (msec)?

A

number of x-rays in beam (quantity)

30
Q

What is the mAs selector

A

mA x Time

number of x-rays in beam

31
Q

What is the kVp selector

A

energy of beam (quality)

number of x-rays (quantity)

32
Q

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

A

(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

33
Q

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

A

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

34
Q

What controls the current to the filament?

A

mA selector

the more current applied, the hotter the filament, the more x-rays produced

35
Q

What does focal spot size influence?

A

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

36
Q

When would you use the small filament in the cathode?

A

for low output exposures where high detail is needed

37
Q

What is the large filament used for?

A

high output exposures

38
Q

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

A

kVp selector

39
Q

what is gradual transition with shades of gray?

A

low contrast

40
Q

what is sharp transition with few shades of gray?

A

high contrast

41
Q

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

A

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

42
Q

what factors increase scatter radiation?

A

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

43
Q

What how do collimators improve image quality?

A

by reducing scatter radiation

44
Q

how do collimators work?

A

they restrict the x-ray beam to a confined region

-located outside tube housing

45
Q

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

A

grid

46
Q

how does scatter radiation decrease image quality?

A

by reducing image contrast

47
Q

How does the grid work?

A

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

48
Q

What impacts resolution of digital radiographs?

A

size of detector elements

49
Q

How is a digital image created?

A

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

50
Q

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

A

2 views at 90 degree angles

51
Q

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

A

subject density and thickness of the object

52
Q

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

A

summation effect

53
Q

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

A

no just superimposed

54
Q

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

A

silhouetting effects

55
Q

What is border effacement?

A

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

56
Q

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

A

magnification

57
Q

The magnification will be greater when?

A

the object is further from the film

58
Q

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

A

distortion

Radiology (3 decks)

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