Intro to CT unit 4 Flashcards
The range of CT numbers used to map signals into shades of gray can be used to describe?
Window width
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?
Window level
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?
Absorption efficiency
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?
indirect
This effect is technologist controlled by increasing or decreasing dose to the patient?
direct
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?
Directly proportional
This technical factor determines the quantity of photons incident on the patient for the duration of the exposure?
mAs
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