Flashcards in Intro to CT unit 4 Deck (41)
The range of CT numbers used to map signals into shades of gray can be used to describe?
Pitch is defined as?
The distance the CT table moves during one complete revolution (360) of the xray tube
What is the definition of High Reproducibility?
The product of capture efficiency, absorption efficiency, and conversion efficiency. It produces the total detector efficiency or dose efficiency.
The location of a CT number scale at which levels of gray are represented by the sample, regulating the optical density of a displayed image. This is the definition of what CT term?
This efficiency detector principle determines how well the detectors convert incoming x-ray photons by the type of tube material used and the thickness of the detectors is termed as which efficiency factor?
When increasing these 3 common factors it will reduce image noise and what does noise look like on a CT Image?
Increasing pixel size, size thickness, mAs
Noise- grainy appearance/mottle
The relative number of x-ray that interacts with a detector can be defined as?
Quantum detection efficiency
Detector dose efficiency affects the following factors by increasing signal to noise ratio:
a. Patient Dose =
b. Scanning (Imaging) Times =
c. Image Quality =
a. Patient Dose = reduce
b. Scanning (Imaging) Times =increase
c. Image Quality =increase
This effect improves image quality without the influence of radiation exposure?
This effect is technologist controlled by increasing or decreasing dose to the patient?
What is considered the most important technique for maintain constant image quality while optimizing radiation dose?
ATCM-Automatic tube current modulation
What is the correlation between the use of mA for slice thickness size?
This technical factor determines the quantity of photons incident on the patient for the duration of the exposure?
How does mAs affect dose?
Increase mAs, increase dose DIRECT
When pitch increases what should happen to mAs in order to keep the Computed Tomography Dose Index (CTDI) constant?
mAs must be increased
How is radiation dose affected by kVp²?
Radiation dose is proportional to the square of the kVp
This technical factor determines the penetrating power of the photons coming from the x-ray tube?
This technical factor defines the beam width for the examination and demonstrates the effective use of the x-ray beam at the detectors?
What is the difference between Translation (Rotation) and Pitch?
Pitch is the distance the CT table moves during one complete revolution of the xray tube, while translation is the distance the table travels between slices during the actual scanning of the pt
What is the typical pitch used in CT & CT Angiography?
1 typical; 2 ct angiography
How does pitch affect dose?
Increasing pitch decreases dose
To increase patient scanning & volume scanning what should happen to pitch?
More detectors have what affect on patient dose?
Decrease dose (inverse)
Why is patient centering so crucial in computed tomography?
Inadequate positioning results in a reduction in imaging quality and increases the pt dose also inadequate pt positioning results in the bowtie filter not to work properly
What is the purpose of a “Bow Tie” filter?
Reduce the beam intensity at the periphery of the beam corresponding to the thinner area of the pts anatomy—started in the second generation
How does time of exposure relate to patient dose?
Increased time increased dose (Directly)
How is distance related to patient dose?
Inversely proportional to the square of distance
For a technologist to receive the least amount of radiation dose when holding a patient, the technologist should stand where?
Stand in a straight line at a right angle with the ct gantry the individual will receive the least amount of radiation dose if individual has to be in the room
What are the 3 Principles that are vital to radiation protection?