Chapter 4 - Image Quality

Question 1

Describes the level of detail that can be seen on an image

Answer 1

Spatial Resolution

Question 2

Spatial resolution relates to how small an object can be seen on a particular imaging system

• a single number value that characterizes the approx. resolution limit of an imaging system
• often considered to be the frequency at which the MTF crosses the 10% level or some other agreed-upon and specified level.

Answer 2

LIMITING Spatial Resolution

Question 3

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)

Answer 3

Spatial domain

Question 4

Most basic measure of the resolution properties of an imaging system; the response of the imaging system to a point source (input to the imaging system)

Answer 4

Point Spread Function (PSF)

- also called the impulse response function

Question 5

An imaging system with the same POINT SPREAD FUNCTION (PSF) at all locations in the fields of view

Answer 5

STATIONARY or SHIFT INVARIANT

Question 6

A systems that has POINT SPREAD FUNCTIONs (PSFs) that vary depending on the position in the field of view

Answer 6

NONSTATIONARY

Question 7

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

Answer 7

LINE SPREAD FUNCTION (LSF)

Question 8

Device required in analog imaging system to measure the optical density as a function of position

Answer 8

Scanning microdensitometer

Question 9

Particularly useful when the spatial resolution characteristics of glare or scatter phenomenon are the subject of interest

Answer 9

EDGE SPREAD FUNCTION (ESF)

Question 10

An integral calculus procedure that accurately describes mathematically what the blurring process does physically

Answer 10

Convolution

Question 11

A process wherein convolution techniques are used to restore (improve) spatial resolution

Answer 11

Deconvolution

Question 12

Another useful way to express the resolution of an imaging system is to make use of the _________.

Answer 12

SPATIAL FREQUENCY DOMAIN

***page 69

Question 13

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

Answer 13

Fourier Transform

Question 14

Resulting data after a spatial domain signal is Fourier transformed

Answer 14

Frequency Domain

Question 15

Perfect line source input

Answer 15

Delta function

Question 16

Sets the upper bound on the spatial frequency that can be detected for a digital detector

Answer 16

Nyquist Frequency

Question 17

The center-to-center distance between adjacent deal extortion elements

Answer 17

Detector Pitch

Question 18

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

-characterized by measurements that pertain to signal-to-noise ratio(SNR) in an image.

Answer 18

Contrast resolution

Question 19

Image noise…the actual distribution of the silver grains is random and is a function of the manufacturing and development process.

-image is formed by millions of silver grains attached to the clear film substrate

Answer 19

Grain noise

Question 20

Typically additive noise from various sources that does not scale with the signal level

• worst in areas of low actual signal in the detector

Answer 20

Electronic noise

Question 21

Image noise that represents a reproducible pattern on the image that reflects differences in the gain of individual detector elements or groups of detector elements

-can be corrected using a flat film algorithm

Answer 21

Structured Noise

Question 22

Characterized by exposing the detector to radiation in the absence of an object

Answer 22

Gain image

Question 23

Measured with no radiation incident on the detector

Answer 23

Offset image

Question 24

Image noise which refers to anatomy in the patient which is not pertinent to the specific imaging system

Answer 24

Anatomical noise

Question 25

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.

Answer 25

Quanta

Question 26

***page 80

Answer 26

Quantum noise

Question 27

A)halfway point in the observed data set B)most frequent observation, the highest point in the histogram C)width of the distribution

Answer 27

A) median B) mode C) range

Question 28

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

Answer 28

Normal distribution(also called the Gaussian Distribution)

Question 29

Statistical distribution governed by only one parameter

Answer 29

Poisson Distribution

Question 30

Characterizes frequency dependence of the noise variance

Answer 30

Noise Power Spectrum (NPS)

Question 31

A type of uncorrelated noise wherein the noise in each pixel of a 2D image is NOT DEPENDENT upon the noise values in any of its surrounding pixels producing a flat horizontal line in the noise power spectrum and no noise correlation

Answer 31

White noise

Question 32

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

Answer 32

Subject contrast

Question 33

...the incident beam of energy from the imaging system will eventually reach the detector(s)... ***page 88

Answer 33

Detector contrast * screen-film radiography- nonlinear response to X-rays * digital radiography- linear response

Question 34

Raw image information is processed into an image that is finally meant for physician viewing

Answer 34

Displayed Contrast

Question 35

Most commonly used look-up table (LUT) in radiological imaging

Answer 35

Window/level

Question 36

An object size-independent measure of the signal level in the presence of noise

Answer 36

Contrast-to-Noise ratio (CNR)

Question 37

Object size DEPENDENT measure of the signal level in the presence of noise

Answer 37

Signal-to-Noise ratio

Question 38

SNR >or= 5 : an object will almost always be recognized (detected) Detection performance continuously degrades as SNR approaches zero

Answer 38

ROSE CRITERION

Question 39

A conceptual visual method for combining the concepts of spatial resolution and contrast resolution

Answer 39

CONTRAST DETAIL DIAGRAM (CD Diagram)

Question 40

Characterization of an X-ray imaging system which describes the over-all frequency-dependent SNR performance of the system - combines concepts of spatial and contrast resolution but the methods of analysis are less visual and more quantitative - defined as the ratio of the SNR2 OUTPUT from the system the SNR2 of the signal INPUT into the system

Answer 40

Detective Quantum Efficiency (DQE)

Question 41

Refers to the probability that the patient is actually abnormal (TP)

Answer 41

Positive predictive value (PPV)

Question 42

Refers to the probability that the patient is actually normal (TN)

Answer 42

NEGATIVE PREDICTIVE VALUE