CT Quick Prep Flashcards
How does filament size affect image quality?
A smaller filament produces images with superior spatial resolution.
When the pitch is increased from 1:1 to 2:1, what happens to the effective slice thickness?
it increases (widened)
In CT, why is the beam heavily filtered?
To reduce beam-hardening artifacts & scatter radiation.
The ability to resolve, as separate forms, small objects that are very close together is called:
Resolution.
The area of pt tissue exposed during a CT scan is controlled by the:
Scan field of view (SFOV).
The ability of the detector to capture transmitted photons and change them to electronic signals is called:
Detector efficiency.
A speckled appearance of the CT image caused by insufficient photons reaching the detectors is known as:
Noise.
What fundamental property accounts for beam hardening artifacts?
The polychromatic nature of the x-ray beam.
What unit quantifies a structure’s ability to attenuate the x-ray beam?
Hounsfield Unit (HU).
What takes up more computer space when stored, raw data or image data?
Raw Data.
A cube of data acquired in CT is called:
A voxel.
What is the process by which different tissue attenuations are averaged to produce a single less accurate pixel reading?
Volume averaging or partial volume effect.
What is the process of converting the data from the attenuation profile to a matrix?
Back Projection
The __________ is often called the “Brain” of the CT system.
Central processing unit (CPU).
An artifact that results from beam hardening & appears on the image as a vague area of increased density in a somewhat concentric shape around the periphery of an image, similar to the shape of a cup is called a:
Cupping artifact.
Visible fluctuations in the image which result in a salt and pepper look is called
Quantum noise.
The CT process be broken down into these three segments:
- data acquisition.
- image reconstruction.
- image display.
The way the detectors are placed, relative to one another, affects the:
Amount of scatter radiation that reaches the image (geometric efficiency).
With what type of scanner are ring artifacts more common?
3rd generation.
What part of the CT system is responsible for sampling each of the detector cells?
The data acquisition system (DAS).
What do the initials ROC stand for in the term “ROC curve”?
Receiver Operating Characteristics.
What is the current of electrons produced by the filament referred to as?
Milliamperes (mAs).
What is the unit of measure for the heat dissipation rate of a system?
KHU (thousand heat units).
What will happen to the CT image if too low an mAs setting is used?
The image will be noisy (grainy)
The amount of CT number variance within the region of interest is called
Standard deviation
What is a disadvantage to a tube with a small focal spot?
It decreases the amount of heat the tube can tolerate.
“The ability to resolve anatomy in an image” is the definition of:
Image quality
What effect does decreasing the slice thickness have on volume averaging?
A thinner slice results in less volume averaging.
What is a two-dimensional square of data called?
A pixel.
The space occupied by the detector collimator plates relative to the surface area of the detector determines the:
Geometric efficiency.
A measure of the beam-attenuation capability of a specific structure is expressed in:
Hounsfield unit (HU), pixel value or CT number.
Why are solid-state detectors sometimes called scintillators?
B/C they emit a flash of light when struck by an x-ray beam.
How can out-of-field artifiacts be avoided?
Proper pt centering within the gantry.
A volume elemnt is also called:
A voxel.
A manifestation that is seen on an image but is not present in the object scanned is called:
An artifact.
The ability to represent small objects & differentiate between closely spaced objects is called:
Spatial resolution.
The mechanism in some CT scanners that allows the x-ray tube to rotate continually in the same direction is known as a:
Slip-ring.
All the measurements obtained from the detector array are called:
Scan data or raw data.
A picture element is known as a:
Pixel.
How will creating a more uniform x-ray beam intensity affect the CT image?
Beam-hardening artifacts will be reduced, therefore the image will be improved.
Sodium iodide, bismuth germanate, cadmium tungstate, cesium iodide, and ceramic rare earth are all materials that have been used for:
Making solid-state detectors.
In the formation of x-ray how will increasing the kilovoltage affect the electrons which will later strike the target material?
Increase thier speed.
Which type of detectors are more sensitive to fluctuations in temperature & moisture?
Solid-state detectors.
What parameter controls the number of detectors used to create an image?
The scan field of view (SFOV).
To create an image, info from the DAS must be translated into a:
Matrix
What device is used to convert the electric signal from the detectors into a digital format?
Analog-to-digital converter (ADC)
What device reduces the beam intensity at the periphery of the beam, corresponding to the thinner parts of a pt?
Bow-tie filters.
The ability of the detector to capture transmitted photons & change them to electronic signals is called:
Detector efficiency.
