22 Questions
The MTF is the ratio of the image to the object as a function of ______ frequency.
spatial
The characteristics of the CT imaging system that contribute to image degradation include ______ element size and concentration.
detector
If the image faithfully represents the object, the MTF of the CT imaging system would have a value of ______.
1
An MTF curve that extends farther to the right indicates better ______ resolution.
spatial
An MTF curve that is higher at low spatial frequencies indicates better ______ resolution.
contrast
Most CT imaging systems are judged by spatial frequency at an MTF equal to ______, sometimes called the limiting resolution.
0.1
Image fidelity is measured by determining the image ______ at various spatial frequencies.
contrast
At a spatial frequency of 1 lp/cm, the variation in image contrast of the image is 0.88 times that of the ______.
object
Imaging system A has a 0.1 ______ at 5.2 lp/cm.
MTF
The ______ resolution of a CT imaging system is expressed in terms of the spatial frequency of the limiting resolution.
spatial
The ______ object size that can be resolved by a CT imaging system is equal to one half the reciprocal of the spatial frequency at the limiting resolution.
absolute
Important measures of imaging system performance that can be evaluated with test objects include ______ generation, contrast resolution, and spatial resolution.
artifact
The system resolution is therefore ______ mm, which represents a 1-mm object separated by a 1-mm interspace.
1
In terms of line pairs, one line and its interspace require at least ______ pixels.
two
Image quality is expressed in terms of ______ resolution, contrast resolution, and noise.
spatial
Computed Tomography image quality is somewhat easier to ______ and quantify.
characterize
______ resolution is a term that refers to the number of pixels utilized in construction of a digital image.
Spatial
______ resolution is the ability to distinguish between differences in intensity in an image.
Contrast
Radiographic ______ is a fluctuation in optical density on radiographic or mammographic images, often as a result of low radiation dose.
noise
The five principal characteristics of CT image quality include ______, contrast resolution, noise, linearity, and uniformity.
spatial resolution
The degree of blurring is a measure of the ______ resolution of the system.
spatial
The image at the interface will be somewhat ______ due to the limitation of spatial resolution.
blurred
Study Notes
Image Quality in CT Imaging
- The loss of faithful image reproduction at higher spatial frequencies is due to limitations of the imaging system.
- Modulation Transfer Function (MTF) is the ratio of image to object as a function of spatial frequency, ranging from 1 (perfect reproduction) to 0 (no information).
- Characteristics contributing to image degradation include collimation, detector element size and concentration, mechanical and electrical gantry control, and reconstruction algorithm.
Modulation Transfer Function (MTF)
- MTF measures the ability of the CT imaging system to reproduce objects of various sizes.
- An MTF curve that extends farther to the right indicates better spatial resolution.
- An MTF curve that is higher at low spatial frequencies indicates better contrast resolution.
Spatial Resolution
- Spatial resolution refers to the number of pixels used to construct a digital image.
- Higher spatial resolution images are composed of a greater number of pixels.
- The degree of blurring at an interface measures the spatial resolution of the system.
Contrast Resolution
- Contrast resolution is the ability to distinguish between differences in intensity in an image.
Image Quality Characteristics
- Five principal characteristics of CT image quality can be numerically assigned: spatial resolution, contrast resolution, noise, linearity, and uniformity.
Measuring CT Image Quality
- A number of methods are available to measure CT image quality.
- Test objects, such as the phantom designed by the American College of Radiology, can be used to evaluate image quality factors.
This quiz explores the limitations of CT imaging systems, including factors that contribute to image degradation, such as collimation and detector element size. It also discusses the Modulation Transfer Function (MTF) and its relationship to spatial frequency.
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