Radiation Safety & Physics of Diagnostic Radiology Flashcards Preview

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Flashcards in Radiation Safety & Physics of Diagnostic Radiology Deck (52):
1

Which two types of imaging are based on the absorption of x-rays?

Radiography and CT 

2

What is another name for x-ray?

photon (can be used interchangeably) 

3

What are x-rays?

type of electromagnetic radiation

4

what are some properties of x-rays? (6 of them) 

No charge or mass

Invisible

Cannot be felt

Travel at speed of light

Penetrate all matter to some degree

Cause ionizations if energy high enough

5

what is ionization?

loss of an electron 

6

why can ionization in DNA be dangerous 

can lead to cell death and mutation (carinogenesis) 

7

T/F: veterinarians are unelievably careless about x-ray safety 

True (we must implement change) 

8

T/F these are good examples of radiation safety 

FALSE!! 

9

what are some consequences of bad radiation safety 

professional reputation 

violation of state regulations 

employee health 

litigation 

10

T/F if you get pregnant you can still receive some radiation dose 

True. 10% of radiation during gestation, must notify employer in writing of pregnancy 

11

what does ALARA stand for?

 

As Low As Resonably Achievable 

12

how is ALARA implemented 

time

distance

shielding 

13

Ways to reduce time exposed to x-rays 

rotate personnel in room 

avoid repeat examinations 

minimize patient holding 

14

T/F increasing the distance between personnel and radiation source reduces exposure significantly 

True (inverse square law is key!)

15

what is the inverse square law?

Intensity of radiation (x rays/unit area) decreases with the square of the distance from the source

i.e double the distance reduces the x-ray intensity to 1/4th (1/2)^2; tripling the distance reduces the intensity to 1/9th (1/3)^2

16

If the distance between the film and the x-ray source decreases from 40” to 30”, how much does radiation intensity at the film change?

By 40^2/30^2

17

what does shielding protect from?

scattered ratiation (won't protect against primary radiation) 

18

what causes scatter?

patient, floor, table, etc 

19

T/F scatter degrades the image and increases personnel dose 

True

20

How can scatter be reduced?

minimize the size of the beam (collimation)

 

21

what is a radiograph?

A picture of the pattern of x rays emerging from the patient

Differential absorption needed to create an image

22

when are x-rays produced?

when high speed electrons strike metal (occurs in an x ray tube) 

23

T/F the anode has a negative charge (-) and the cathode has a postive charge (+)

False

the anode is positive (+) and the cathode is negative (-) 

24

how does the filament (-) work?

current causes heating and electrons "boil" off 

25

T/F the number of x rays produced is proportional to current (mA) and time current is "on" (s)

True (this is your mAs) 

26

T/F doubling the mAs double the number of x rays 

True 

27

T/F the longer the time (s) the more electrons are produced 

true 

28

T/F the target and the filament are made of tungsten 

True 

29

T/F the voltage between target-filament makes target positive to attract the negatively charged electrons 

True

30

what is kVp

voltage quantified 

 

31

what does increasing kVp do?

greater voltage difference 

electrons travel faster 

have more kinetic energy 

create higher energy x rays 

32

how do we keep the target from melting?

tungsten has a high melting point 

target rotates to dissipate heat 

33

what are the mAs and kVp setting important for avoiding

over or underexposure 

34

this image is over/underexposed?

underexposed (either kVp or mAs is too low) 

35

this image is under/overexposed/perfect?

overexposed (either kVp or mAs is too high) 

36

what does it mean when your radiograph is too light?

too few x-rays hit the detector (underexposed)

fix: increase mAs (more x rays) or increase kVp (higher energy) 

37

T/F many combinations of mAs and kVp lead to suitable exposure 

True 

38

whether kVp or mAs is changed will effect the ______

image contrast 

39

what is high contrast?

low kVp, high mAs 

x rays are less penetrable, few shades of grey 

40

what is low contrast?

high kVp, low mAs 

x rays are more penetrable, absorption is more uniform, many shades of grey 

41

what mAs/kVp should be used in the thorax?

high kVp, low mAs

air provide contrast-lungs!!

42

what mAs/kVp should be used in abdomen

low kVp, high mAs

fat provides the contrast-subject contrast needs to be maximized by technique (some animals fatter than others) 

"when you're fat you have a high body mAs index"

43

what is needed to make an image 

absorption and scatter 

44

what are some problems caused by scatter 

degrades image 

increases personnel dose 

45

why are grids used?

"intercepts" scatter from patient before it reaches film 

46

when are grids generally used?

when the patient is more than 10 cm thick 

47

which setting needs to be changed when using a grid 

mAs

need 2-3x more photons due to absorption of primary beam by lead 

48

where should the grid be positioned?

 

between the patient and the cassette

49

what are the 2 methods for recording the x ray image 

analog and digital 

50

what are the components of analog image recording system?

cassette

intensifying screens

x ray film 

51

what does the intensifying screen do?

converts x ray photons to light photons 

one x ray photons= many light photons 

light photons expose the x ray film (sensitive to light) 

>90% of blackness due to light vs x rays 

52

advantages of intensifying screens 

100x reduction in mAs 

reduced movement artifact 

reduced patient exposure 

reduced personnel exposure 

increased tube life