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RTE1418 Introduction to Radiologic Technique > Spatial Resolution > Flashcards

Spatial Resolution Flashcards

1
Q

What are the three different ways “Spatial Resolution” can be defined

A

a. Smallest structures in an image measured in LP/mm
b. Sharpness of structural lines on an image
c. Ability to image adjacent objects separately

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2
Q

What is the unit of measurement for spatial resolution?

A

line pairs/mm

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3
Q

What do the line pairs represent?

A

the smallest size object the imaging system is able to visualizing

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4
Q

define penumbra:

A

unsharpness in the image

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5
Q

define umbra:

A

a lack of unsharpness in the image

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6
Q

8 factors affecting spatial resolution

A

OID
SID
patient motion
filament size
anode angle
image display
size distortion
shape distortion

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7
Q

define OID:

A

object to image distance

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8
Q

increasing OID will lead to:

A

magnification

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9
Q

decreasing OID will lead to:

A

less magnification

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10
Q

What has the largest impact on magnification?

A

OID

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11
Q

Why does OID create magnification?

A

beam divergence

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12
Q

How do you double the size (2x mag.) of a body part?

A

always put the part half way between IR and source

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13
Q

Which of the following has the greatest effect on reducing object magnification?

A

decreasing OID

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14
Q

OID produces magnification of the part… why is this undesirable?

A

penumbra

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15
Q

What has a greater effect on spatial resolution?

A

OID

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16
Q

What is the best way to reduce focal spot blur (besides choosing the filament)?

A

decrease OID

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17
Q

What is the greatest way to reduce the effects of OID?

A

increase SID

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18
Q

The best way to minimize magnification is to:

A

decrease OID
increase SID

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19
Q

define SID:

A

anode target (source) to IR

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20
Q

increasing SID will:

A

decrease magnification

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21
Q

decreasing SID will:

A

increase magnification

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22
Q

How is SID measured?

A

AFS to IR

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23
Q

Decreasing SID does what to size distortion?

A

increases

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24
Q

Increasing distance (SID) requires that the mAS be _____ in order to maintain image receptor exposure

A

increased

25
Q

The more magnified an object,

A

the less the spatial resolution

26
Q

SOD is defined as:

A

distance between anode target and the object imaged

27
Q

magnification formula:

A

MF = SID/SOD

28
Q

actual size formula:

A

actual size = image size/MF

29
Q

SOD formula:

A

SID - OID

30
Q

define AFS:

A

area of the anode target struck by electrons

31
Q

Which two factors determine the size of the AFS

A

filament size
anode target angle

32
Q

the larger the AFS:

A

the worse the spatial resolution

33
Q

define EFS:

A

area projected onto patient

34
Q

the smaller the filament size:

A

the smaller the EFS and better the spatial resolution

35
Q

the smaller the anode angle:

A

the smaller the EFS and better the spatial resolution

36
Q

what size filament will always provide better spatial resolution?

A

small

37
Q

Why does a smaller filament produce a better spatial resolution?

A

less divergence (less penumbra)

38
Q

why does a larger filament create penumbra?

A

because there is more divergence

39
Q

define focal spot blur:

A

blurred region of a radiograph that the tech has little control

40
Q

decreasing OID will do what to focal spot blur?

A

reduce

41
Q

The line focus principle states:

A

An anode angle of less than 45° will produce a smaller EFS than the FSS

42
Q

The advantage of the line focus principle is that it simultaneously improves:

A

spatial resolution and heat capacity

43
Q

why would we want to make the AFS larger than the filament size?

A

more ability to dissipate heat

44
Q

lesser angles produce:

A

sharper images

45
Q
  1. larger anode angle = ______ heat dissipation
  2. smaller anode angle = ______ heat dissipation
  3. larger filament = ______ AFS
  4. smaller filament = ______ AFS
  5. larger EFS = ______ beam div. and ______ spatial resolution
  6. smaller EFS = ______ beam div. and ______ spatial resolution
A
  1. greater
  2. less
  3. larger
  4. smaller
  5. increased; decreased
  6. decreased; increased
46
Q

patient motion will always cause:

A

a loss in spatial resolution

47
Q

Two types of distortion:

A

size and shape

48
Q

Which type of image distortion is called “true distortion?”

A

shape

49
Q

Why is shape distortion called “true distortion?”

A

it is actually changing the shape of something

50
Q

define shape distortion:

A

distortion of an objects shape

51
Q

What are the two types of shape distortion?

A

elongation and foreshortening

52
Q

Which type of shape distortion is created by the angling of the part?

A

foreshortening

53
Q

Which type of shape distortion results from angulation of the tube or IR?

A

elongation

54
Q

Which of the following can be done to decrease size distortion?

A

increase SID
decrease OID

55
Q

Is shape distortion always bad?

A

no

56
Q

size distortion is only influenced by these 3 factors:

A

SID
OID
SOD (source to object)

57
Q

geometric factors affecting image quality:

A

magnification
distortion (shape and size)
focal spot blur

they all cause blur!

58
Q

Which set of factors will provide the greatest spatial resolution?

A

small filament, small anode angle, small OID, large SID

RTE1418 Introduction to Radiologic Technique (12 decks)

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