Image Quality Flashcards
This describes the level of detail that can be seen on an image.
Spatial resolution
Spatial resolution relates to how small an object can be seen on a particular imaging system -and this would be the limiting spatial resolution.
In radiology, images vary in size from small spot images acquired in mammography (50 mm x 50 mm) to the chest radiography, which is ____________.
350 mm x 430 mm
These images are acquired and viewed in the spatial domain.
This refers to the two dimensions of a single image, or three dimensions of a set of tomographic images such as computed tomography (CT) or magnetic resonance imaging (MRI).
Spatial domain
This is the most basic measure of the resolution properties of an imaging system, and perhaps the most intuitive as well.
Point spread function (PSF)
It is also called the impulse response function.
The diameter of the “point” input should theoretically be infinitely small, but practically speaking, the diameter of the point should be _____________ than the width of the detector element in the imaging system being evaluated.
Five to ten times smaller
An imaging system with the same PSF at all locations in the field of view is called _____________, while a system that has vary depending on the position in the field of view is called _____________.
Stationary or shift invariant
Nonstationary
When an imaging system is stimulated with a signal in the form of a line, the ___________ can be evaluated.
Line spread function
For analog imaging system such as radiographic film, a device called a ______________ is required to measure the optical density as a function of position.
Scanning microdensitometer
In some situations, PSF and LSF measurements are not ideally suited for a specific imaging application, where the _____________ can be measured.
Edge spread function (ESF)
This is particularly useful when the spatial distribution characteristics of glare or scatter phenomenon are the subject of interest - since a large fraction of the field of view is stimulated, low-amplitude effects such as glare or scatter (or both) become appreciable enough in amplitude to be measurable.
This is an integral calculus procedure that accurately describes mathematically what the blurring process does physically.
Convolution
A mathematical process that describes physical blurring phenomena
When convolution techniques can be used to restore (improve) spatial resolution. What is this process?
Deconvolution
While it can improve spatial resolution, it also amplifies the noise levels in the image
It is a method for decomposing a function such as a gray scale profile into the sum of a number of sine-waves.
Each sine wave has three parameters that characterized its shape: amplitude, frequency, and phase.
Fourier series
This is an algorithm that decomposes a spatial or time domain signal into a series of sine waves, that when summed, replicate that signal.
Fourier transform
Once a spatial domain signal is Fourier transformed, the resulting data are considered to be in what domain?
Frequency domain
This refers to the ability to detect very subtle changes in gray scale an distinguish them from the noise in the image.
Contrast resolution
It is characterized by measurements that pertain to the signal-to-noise-ration in an image.
This relates to how close one to gets to the “truth”
Accuracy
This is a description of variation, scatter, or reproducibility in a measurement.
Precision
Measurements with low precision have higher level of noise.
This results in screen film radiography, where the image is formed by millions of silver grains attached to the clear film substrate.
Grain noise
In general, grain noise is too small to be resolved in general radiography.
This is typically additive noise from various sources that does not scale with the signal level.
Electronic noise
This can be from thermal noise, shot noise, and other electronic noise sources.
When signal levels are low, the added noise can be substantial and can contribute appreciably to the overall noise levels in the image.
What are ways to reduce electronic noise?
Cooling the detector system to reduce thermal noise
Designing in noise reduction circuitry
Shielding electronics to avoid stray electronic signal induction
This represents reproducible pattern on the image that reflects differences in the gain of individual detector elements or groups of detector elements.
Structured noise
This refers to anatomy in the patient which is not pertinent to the specific imaging examination.
Anatomical noise
Refers to noise resulting from the use of a very low number of quantum in medical images involving x-rays and gamma rays.
Quantum noise
This is the fundamental contrast that arises in the signal, after in has interacted with the patient but before it has been detected.
Subject contrast
This is a component of subject contrast that relates to the actual anatomical or functional changes in the patient’s tissues, which give rise to contrast.
Intrinsic component/ factor
A factor in subject contrast that relates to how the image-acquisition protocol can be optimized to enhanced subject contrast.
Extrinsic factor
This is an object size-independent measure of the signal level in the presence of noise.
This is a good metric for describing the signal amplitude relative to the ambient noise in an image, and this is particularly useful in simple objects.
Contrast-to-noise ratio
This is most applicable when test objects that generate a homogeneous signal level are used.
This is a metric similar to the CNR, except that the size and shape of the object is explicitly included in the computation.
Signal-to-noise ratio
This does not require the test object that generates the signal to be homogeneous.
