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202 MEDIMAGE > 13. Radiographic image quality and contrast media > Flashcards

13. Radiographic image quality and contrast media Flashcards

1
Q

what does absorbed radiation create on the image in terms of appearance and brightness

A

increased brightness and white areas

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2
Q

what does transmitted radiation create on the image in terms of appearance and brightness

A

decreased brightness and black areas

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3
Q

what are the 3 factors in terms of anatomy visibility

A

brightness

contrast

signal to noise ratio

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4
Q

what are the 3 factors in terms of how accurately the image represents the anatomy (sharpness)

sharpness/accuracy of structural lines

A

spatial resolution

sharpness

distortion

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5
Q

how is image brightness evaluated

2 things

A

by the amount of luminance/light emission of the display monitor

the amount of density or overall blackness after processing

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6
Q

what is image brightness

A

amount of luminance/light emission from an image or display

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7
Q

what does brightness depend on

2 things

A

absorption and transmission of x-ray through tissue

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8
Q

what is the exposure intensity

A

amount and energy of x-rays reaching an area of the IR

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9
Q

the exposure intensity must be high enough to__ and low enough to __

A

high enough to overcome quantum noise

low enough to minimise patient dose

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10
Q

what causes noise in terms of primary exposure factors

A

mAs too low = grainy images

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11
Q

what is image contrast

A

differences in brightness/density levels to differentiate between anatomic tissues

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12
Q

the range of brightness levels/contrast is a result of what

A

the tissues differential absorption of the x-ray photons

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13
Q

what is subject contrast

what 2 things is it the result of

A

different densities in the patient

result of absorption characteristics of the anatomic tissue radiographed and the quality of the x-ray beam

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14
Q

what is the difference between the gray scale and scale of contrast

A

gray scale = number of different shades of grey that can be stored and displayed in a digital image

scale of contrast = range of densities visible on film

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15
Q

higher contrast results from what

A

great differences in radiation absorption between tissues that vary greatly in composition

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16
Q

what is contrast resolution

A

ability of IR to distinguish between tissues with similar subject contrast

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17
Q

what is spatial resolution

A

how much system is able to give info about detail by distinguishing between different structures even though the structures might have similar appearance to each other

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18
Q

what does spatial resolution refer to

A

the smallest object that can be detected in a digital image

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19
Q

what is sharpness/spatial resolution

A

accuracy of representing anatomical structural boundaries

20
Q

what 2 things affects the sharpness/spatial resolution of an image

A

focal spot size

magnification

21
Q

what is distortion

what 2 features of the anatomic part is involved

A

misrepresentation of either the size or shape of the anatomic part

22
Q

what are the 3 things that can affect distortion

A

CR alignment or the x-ray tube

CR alignment of the part

CR alignment of IR

23
Q

what are the 2 types of shape distortion that can occur

A

foreshortening

elongation

24
Q

what is shape distortion

A

change in the imaged proportions of an object

25
Q

what 3 things is shape distortion affected by

A

orientation and alignment of object, IR and central ray

26
Q

how is the size and number of pixels in the matrix related to the spatial resolution

A

larger number of pixels = greater spatial resolution

smaller pixel size = capture smaller entities and higher resolution

27
Q

anatomy must be aligned how to avoid shape distortion

in terms of the IR and x-ray beam

A

anatomy must be parallel to the IR plate and perpendicular to the x-ray beam

28
Q

what is size distortion and what does it affect

A

magnification

affects accuracy of representing anatomical structural boundaries

29
Q

what 3 things is size distortion due to

A

longer OID

shorter SID

larger focal spot size

30
Q

what should be done to the SID and OID to get rid of sharpness

A

shorter OID

extend/larger SID

31
Q

what is motion unsharpness

A

decrease in sharpness resulting from voluntary or involuntary patient motion

32
Q

what is scatter

A

unwanted exposure to the image receptor resulting in fog

33
Q

what is scatter the result of

A

compton interactions

34
Q

what does scatter and fog do to the image contrast

A

decreases contrast

35
Q

what do you reduce scatter via the primary exposure factors

A

decrease kV

36
Q

what is quantum noise

what is it dependent on

A

visible as brightness or density fluctuations and is photon dependent

too few x-ray photons results in increased quantum noise

37
Q

what is contrast media

A

group of chemical agents developed to aid the characterization of pathology by improving the contrast resolution of an imaging modality

38
Q

what are the 3 types of contrast administration

A

swallowed/orally

enemia/rectally

intravenously/intra-arterially

39
Q

what is a barium enema

what structures does it visualise

A

into large colon to see ascending, transverse and descending colon

40
Q

what are positive contrast in terms of what it does to the attenuation

A

increases attenuation

41
Q

what are 2 examples of positive contrast

A

barium, iodine

42
Q

what may need to be done when using positive contrast

A

may need to adjust exposure factors

43
Q

what are negative contrast in terms of what it does to the attenuation

A

decreases attenuation

44
Q

what is an example of negative contrast

A

air

45
Q

do exposure factors need to be adjusted when using negative contrast

A

no

46
Q

why can contrast agents be seen on images

A

due to differences in tissue density (increased x-ray absorption based on higher density)

202 MEDIMAGE (18 decks)

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