Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Physics > AIM: Ch 4: Image Quality > Flashcards

AIM: Ch 4: Image Quality Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards AP® Physics flashcards
1
Q

It describes the level of detail that can be seen on an image. In simple terms, it relates to how small an object can be seen on a particular imaging system.

A

Spatial resolution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Size of the picture element in an image is called

A

Pixel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

T/F: While it is true that one cannot resolve an object that is smaller than the pixel size, it is also true that one may be able to detect a high-contrast object that is smaller than the pixel size if its signal amplitude is large enough to significantly affect the gray scale value of that pixel.

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

T/F: In many cases, it is not the pixel size that is the limiting factor in spatial resolution.

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

The ____ refers to the two dimensions of a single image, or to the three dimensions of a set of tomographic images such as computed tomography (CT) or magnetic resonance imaging (MRI).

A

Spatial domain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

The ____ is the most basic measure of the resolution properties of an imaging system, and is by definition the response of the imaging system to that point input

A

Point spread function (PSF)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

The PSF is also called the ____

A

Impulse response function

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

The ____ is a two-dimensional (2D) function, typically described in the x and y dimensions of a 2D image

A

PSF

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

An imaging system with the same PSF at all locations in the field of view is called ____, while a system that has PSFs that vary depending on the position in the field of view is called ____

A

Stationary or shift invariant, nonstationary

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

The PSF describes the extent of ____ that is introduced by an imaging system, and this is the manifestation of physical events during the image acquisition

A

Blurring

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

When an imaging system is stimulated with a signal in the form of a line, the ____ can be evaluated

A

Line spread function (LSF)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

It is a measure of gray scale as a function of position

A

Profile

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

For an analog imaging system such as radiographic film, a device called a ____ is required to measure the optical density as a function of position.

A

Scanning microdensitometer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

____ is an integral calculus procedure that accurately describes mathematically what the blurring process does physically

A

Convolution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Use of such a kernel in data analysis is also called a

A

Boxcar average or running average

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

It is worth noting that if the kernel was [0, 0, 1, 0, 0], G would be ____ to H. This kernel is called a ____ function.

A

Equal, delta

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

____-dimensional convolution techniques are also used in medical imaging processing

A

Three

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Convolution is a mathematical process that describes physical blurring phenomena, but convolution techniques can be used to restore (improve) spatial resolution as well—in such cases the process is called ____

A

Deconvolution

While deconvolution can improve spatial resolution in some cases, it also amplifies the noise levels in the image.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

The spatial resolution ____ as the width of the RECT function increases

A

Decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

It is an algorithm that decomposes a spatial or time domain signal into a series of sine waves that, when summed, replicate that signal

A

Fourier transform

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

The ____ converts a temporal or spatial signal into the frequency domain, while the ____ converts the frequency domain signal back to the temporal or spatial domain

A

Fourier transform, FT[]
Inverse Fourier transform, FT21[]

Fourier transform = toward Frequecy domain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

____ are used to perform the filtering procedure in filtered back projection, for CT reconstruction

A

Fourier transforms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

____ are used in MRI to convert the measured time domain signal into a spatial signal.

A

Inverse Fourier transforms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

The ____ is used to determine the MTF in experimental settings

The Modulation Transfer Function, MTF(f)

A

LSF

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

A perfect line source input (called a ____), it turns out, is represented in the frequency domain by an infinite number of sinusoidal functions spanning the frequency spectrum

A

Delta-function

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

The limiting spatial resolution is often considered to be the frequency at which the MTF crosses the ____, or some other agreed-upon and specified level.

A

10% level

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

It is the accepted standard for the rigorous characterization of spatial resolution

A

MTF

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

It sets the upper bound on the spatial frequency that can be detected for a digital detector system with detector pitch (delta).

A

Nyquist frequency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Give the formula for the Nyquist frequency

A

FN = 1/2 (delta)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

T/F: If a sinusoidal signal greater than the Nyquist frequency were to be incident upon the detector system, its true frequency would not be recorded, but rather it would be aliased.

A

True

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

It occurs when frequencies higher than the Nyquist frequency are imaged

A

Aliasing

Aliasing is visible when there is a periodic pattern that is imaged, such as an x-ray antiscatter grid, and aliasing appears visually in many cases as a Moiré pattern or wavy lines.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Refers to the center-to-center distance between adjacent detector elements

A

Detector pitch

33
Q

T/F: For a detector where the detector pitch (the center-to-center distance between adjacent detector elements) is D, the width of each detector element (a) is greater than D, that is, a > D

A

False

34
Q

T/F: For a system which has an MTF defined by the sinc function, the possibility of aliasing is high since the MTF still has nonzero amplitude above FN. An imaging system that has an MTF defined by the sinc function is performing at its theoretical maximum in terms of spatial resolution.

A

True

35
Q

It refers to the ability to detect very subtle changes in gray scale and distinguish them from the noise in the image

A

Contrast resolution

36
Q

T/F: Contrast resolution is characterized by measurements that pertain to the signal-to-noise ratio (SNR) in an image.

A

True

37
Q

Accuracy versus precision: In medical images, ____ has to do with the amount of noise in the image

A

Precision

PrecisioN = Noise

38
Q

In the case of x-ray and gamma ray imaging, which are typically quantum limited, precision can almost always be improved by collecting more photons (quanta) to make the image. How is this accomplishes?
a. By increasing the time of the image acquisition
b. Turning up the intensity of the source (or injecting more isotope)
c. Either and/or all of the above
d. None of the above

A

C. Either and/or all of the above

39
Q

T/F: Grain noise is not a factor when reading a film radiograph on a view box

A

True

40
Q

Grain noise is based on the actual distribution of the ____ and may be possible to observe in screen-film mammography, and thus, they would become a source of image noise in that instance

A

Silver grains

41
Q

This noise refers to the electrons that are added to the signal that are not the result of signal detection events

A

Electronic noise

Can be from thermal noise, shot noise, and other electronic noise sources

42
Q

The following are the ways to reduce electronic noise:
a. Cooling the detector system to reduce thermal noise
b. Designing in noise reduction circuitry (e.g., double correlated sampling)
c. Shielding electronics to avoid stray electronic signal induction
d. All of the above

A

d. All of the above

43
Q

Results when groups of detector elements that are read out have different offset noise and gain characteristics in digital detector systems

A

Structured or fixed pattern noise

Structured noise can be corrected using a flat field algorithm

44
Q

These two calibration images can then be used to correct for structured noise using the so-called flat field correction algorithm

A

Gain image and offset image

The key to correcting for structured noise is that it is spatially constant for a period of time. This allows the offset and gain factors for each individual detector element to be characterized by exposing the detector to radiation in the absence of an object (the so-called gain image)

The offset image is measured with no radiation incident on the detector.

45
Q

A splash of iodinated contrast agent on the input surface of an image intensifier (II) used in angiography will cause a ____ that is always at the same location in the image (except when magnification modes are applied)

A

Dark spot

46
Q

Flat field correction approaches will correct for these blemishes as well, but if the II is cleaned and the flat field images are not recomputed, then the blemish will be overcompensated for—it will be a ____

A

Bright spot

47
Q

It is the pattern on the image that is generated by patient anatomy that is always present but not important for the diagnosis

A

Anatomy noise

48
Q

These are performed primarily to reduce anatomical noise

A

Temporal and dual-energy subtraction methods

49
Q

T/F: Much of the power of tomography, then, is in its ability to reduce anatomical noise through spatial isolation

A

True

50
Q

It refers to any number of particles or objects that can be counted, such as electrons, x-ray photons, optical photons, or even brush strokes on impressionist paintings.

A

Quanta

51
Q

This noise results from the low numbers of quanta for most medical images involving x-rays or gamma rays

A

Quantum noise

52
Q

Point in the distribution where 50% of the observations are greater, and 50% are less

A

Median

53
Q

Most frequent observation, the highest point in the histogram

A

Mode

54
Q

Most widely used statistical distribution in scientific analysis and other observational settings

A

Normal distribution, also called the gaussian distribution

55
Q

The frequency dependence of the noise variance is characterized by the ____, where for a 2D image I(x,y)

A

Noise power spectrum, NPS(f)

The NPS(f) yields an informative, frequency-dependent measure of how an imaging system operates on the noise input into the system. NPS is essentially a frequency-dependent breakdown of the variance, and indeed the integral of the NPS over all frequencies equals the variance^2

56
Q

If the noise in each pixel of a 2D image is not dependent upon the noise values in any of its surrounding pixels, then there will be no noise correlation and the NPS(f) will essentially be a flat, horizontal line (Fig. 4-28). This type of uncorrelated noise is called ____

A

White noise

57
Q

It is the fundamental contrast that arises in the signal, after it has interacted with the patient but before it has been detected

A

Subject contrast

58
Q

Intrinsic vs Extrinsic Component of Subject contrast:
a. It relates to the actual anatomical or functional changes in the patient’s tissues, which give rise to contrast
b. It relates to how the image-acquisition protocol can be optimized to enhance subject contrast

A

a. Intrinsic
b. Extrinsic

59
Q

T/F: The detector system can have a profound impact on how the subject contrast incident upon it is converted to the final image

A

True

60
Q

The most commonly used LUT in radiological imaging is called

A

Window/level

61
Q

Image processing method where the raw 14-bit image is collapsed down to a displayable 10-bit image

A

Blurred mask subtraction

62
Q

It is an object size-independent measure of the signal level in the presence of noise

A

Contrast-to-Noise Ratio (CNR)

63
Q

A metric where size and shape of the object is explicitly included in the computation

A

Signal-to-Noise Ratio (SNR)

64
Q

This states that if SNR >/= 5, then an object will almost always be recognized (detected), but that detection performance continuously degrades as SNR approaches zero

A

Rose Criterion

65
Q

This metric is most applicable when test objects that generate a homogeneous signal level are used—that is, where the mean gray scale in the signal ROI is representative of the entire object

A

Contrast-to-Noise Ratio (CNR)

66
Q

Example uses of this metric include optimizing the kV of an imaging study to maximize bone contrast at a fixed dose level, computing the dose necessary to achieve a given CNR for a given object, or computing the minimum concentration of contrast agent that could be seen on given test phantom with fixed dose.

A

Contrast-to-Noise Ratio (CNR)

67
Q

This metric does not require the test object that generates the signal to be homogeneous; however, the background does need to be homogeneous in principle—a series of gaussian “blobs” is used to illustrate this point

A

Signal-to-Noise Ratio (SNR)

68
Q

It is a conceptual, visual method for combining the concepts of spatial resolution and contrast resolution.

A

Contrast detail diagram, or CD diagram

It is a subjective visual test. The use of CD diagrams unites the concepts of spatial resolution (i.e., detail) and contrast resolution (i.e., SNR) on the same graph.

69
Q

It is a characterization of an x-ray imaging system, used by imaging scientists, which describes the overall frequency-dependent SNR performance of the system

A

Detective Quantum Efficiency of an imaging system

70
Q

It describes how well an imaging system processes signal

A

MTF(f)

71
Q

It describes how well an imaging system processes noise in the image.

A

NPS(f)

72
Q

Unit of DQE(f)

A

1/mm^2

73
Q

T/F: The DQE(f), is a frequency-dependent description, and at zero frequency (f=0) in the absence of appreciable electronic noise, the DQE(0) essentially converges to the detector’s quantum detection efficiency, the QDE.

A

True

74
Q

Image quality can be quantified using a number of metrics that have been discussed above. Ultimately, however, the quality of an image relates to how well it conveys diagnostic information to the interpreting physician. This can be tested using the concept of the ____ curve

A

Receiver operating characteristic (ROC)

75
Q

Starting point of ROC analysis

A

2 x 2 decision matrix (sometimes called the truth table)

76
Q

a. True-negative fraction
b. True-positive fraction

A

a. Specificity
b. Sensitivity

True SpEN and SnOP

77
Q

T/F: An ROC curve is a plot of the TPF as a function of the FPF, which is also the specificity as a function of (1-sensitivity)

A

False

An ROC curve is a plot of the TPF as a function of the FPF, which is also the sensitivity as a function of (1-specificity)

78
Q

It refers to the probability that the patient is actually abnormal (TP), when the diagnostician says the patient is abnormal (TP + FP)

A

Positive predictive value

79
Q

It refers to the probability that the patient is actually normal (TN), when the diagnostician says the patient is normal (TN + FN).

A

Negative predictive value

Physics (16 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions