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Physics - Common Equipment > Chapter 9 > Flashcards

Chapter 9 Flashcards

1
Q

What determines the overall quality of an image?

A

Visibility of anatomic structures and the accuracy of their structural lines (sharpness)

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2
Q

Brightness and contrast are used to describe an images:

A

Visibility

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3
Q

How is image sharpness acheived?

A

Maximizing spatial resolution and minimizing distortion

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4
Q

How is visibility acheived?

A

Properly balancing brightness and contrast

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5
Q

What is brightness?

A

The amount of luminance of a display monitor

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6
Q

Brightness can easily be adjusted in digtial imaging because the images are formed by:

A

Numerical data

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7
Q

How is brightness adjusted in digital imaging?

A

Adjusting technique or adjusting window during post processing

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8
Q

Why should a radiographer repeat the image if it is way too dark or too bright?

A

Windowing can correct brightness but it cannot correct over or under penetrated

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9
Q

What does a receptor need to properly utilize as much of the remnant beam as possible?

A

Wide dynamic range

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10
Q

What should the radiographer evaluate before sending an image to PACS?

A

Proper exposure, not just brightness

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11
Q

What is saturation?

A

Receptor is over exposed, resulting in an image that is burnt out and cannot be corrected with windowing

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12
Q

What causes an image to look grainy?

A

Receptor is underexposed

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13
Q

What are exposure indicators?

A

Numeric values that indicate the amount of radiation exposure received

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14
Q

What is image contrast?

A

The exhibited difference in brightness levels within an image

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15
Q

What causes an image to have a washed out appearance?

A

Too little contrast

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16
Q

What causes an image to have a black and white appearance

A

High contrast

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17
Q

When do we want high contrast vs low contrast?

A

High - bony structures
Low - Soft tissue

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18
Q

What is radiographic contrast?

A

Combined results of dynamic range, radiation quality, and the characteristics of tissues being imaged

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19
Q

What is subject contrast?

A

Refers to the absorption characteristics of the tissues being imaged

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20
Q

What tissue characteristics affect contrast?

A

Thickness, density, and effective atomic number

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21
Q

How does high radiation quality alter subject contrast?

A

The stronger the beam, the more likely it is to scatter or pass through the body

Less chance of absorption results in fewer brightness differences - lower contrast

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22
Q

How does high absorption affect subject contrast?

A

More brightness differences in the image, but can also degrade image quality of IR is not properly exposed

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23
Q

Contrast is a complex image attribute, it is more _______ than brightness

A

Subjective

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24
Q

What is grayscale?

A

The number of different shades of gray diplayed

25
Q

What is used to describe an imaging systems ability to differentiate between small structures that attenuate radiation similarly?

A

Contrast Resolution

26
Q

What is high contrast resolution?

A

Able to differentiate between small, similar structures

27
Q

Benefit of increased pixel depth?

A

Provides a larger amount of grays = higher contrast resolution

28
Q

How is contrast adjusted once an image is processed?

A

Adjusting window width

29
Q

What is spatial resolution?

A

Used to evaluate the accuracy of anatomic structural lines

30
Q

How does pixel size impact spatial resolution?

A

The larger the pixels, the less spatial resolution

31
Q

Pixel size formula:

A

FOV/matrix size

32
Q

If displayed FOV is increased for a fixed matrix size, then pixel size is:

A

Increased

33
Q

If matrix size is increased for a fixed FOV, then pixel size is:

A

Decreased

34
Q

The relationship between FOV and matrix size is:

A

Inversely proportional

35
Q

Resolution in digital imaging is limited by pixel size and:

A

spatial frequency

36
Q

What is spatial frequency?

A

Unit of line pairs per millimeter (lp/mm)

37
Q

Relationship between objects and spatial frequency?

A

Smaller objects have greater spatial frequency

Larger objects have lower spatial frequency

38
Q

What makes up a line pair?

A

A line and a space; a white and black line

39
Q

Relationship between spatial frequency and resolution?

A

Directly proportional - the more line pairs, the greater the resolution

40
Q

What is MTF?

A

Modulation Transfer Function - measure of an imaging systems ability to display the contrast of anatomic objects in varying size

41
Q

What are the values for MTE?

A

0 to 1

0 - no difference in brightness

1- maximum difference in brightness

42
Q

What is DQE?

A

Detective Quantum Efficiency - measurement of how efficiently an image receptor is in converting x-ray exposure it receives into a quality radiographic image

43
Q

What does 100% DQE represent?

A

IR would be able to convert all of the radiation it receives into an image with zero information lost

44
Q

What is distortion?

A

The misrepresentation of the anatomic part in imaging

45
Q

What is size distortion?

A

Refers to the increased size of the anatomic structure

46
Q

What has a strong effect on size distortion?

A

SID
OID

47
Q

Increased OID, results in ______ magnification

A

Increased

48
Q

Increased SID, results in ________ magnification

A

Decreased

49
Q

What are the two forms of shape distortion?

A

Elongation and foreshortening

50
Q

Because digital receptors can detect lower levels of radiation, they are _____ sensitive to scatter

A

More

51
Q

What is quantum noise (mottle)?

A

Caused by too little radiation reaching the IR - gives a grainy appearance

52
Q

Method of describing the strength of radiation exposure compared with the amount of noise present in a digital image

A

Signal-to-noise Ratio (SNR)

53
Q

What is signal?

A

Amount of radiation exposure captured by the IR

54
Q

What causes noise?

A

Not enough radiation hits the IR

55
Q

How can noise be decreased?

A

Increasing signal, however, this also increases patient dose

56
Q

What is the method of describing contrast resoltuion compared with the amont of noise present in an image?

A

Contrast-to-noise ratio (CTN)

57
Q

How does noise affect CNR and SNR?

A

Negatively

58
Q

What are artifacts?

A

Unwanted darkness or brightness level

Physics - Common Equipment (7 decks)

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