+
Cards In This Set
| Front | Back |
|
What are the 5 key influences on CT parameter selection?
|
*Contrast Resolution
*Spatial Resolution
*Temporal Resolution
*Image Noise
*Patient Dose
|
|
What is contrast resolution?
|
The ability to differentiate small differences in density on the image.
|
|
What is spatial resolution?
|
A measure of the size of the smallest object that can be visualized in an image.
|
|
What is temporal resolution?
|
Refers to the precision of a measurement with respect to time.
|
|
When helical scanning became available, the exam times ___________.
|
Decreased
|
|
What is image noise?
|
Noise appears in a CT image as a point-to-point fluctuation in the CT number within a uniform material, it makes the image look grainy or speckled.
|
|
What is the easiest way of increasing the # of photons that contribute to the pixels in the image?
|
Increase the tube current or the scan time.
|
|
What happens to patient dose when tube current or scan time is increased.
|
Patient dose increases.
|
|
What is patient dose?
|
The dose is the amount of ionizing radiation absorbed by the patient per unit mass.
|
|
What parameters in CT affects patient dose?
|
*scan rotation time *slice thickness
*tube current *table increment
*the peak tube voltage *pitch
*anatomical coverage desired
|
|
What is attenuation?
|
The progressive reduction of the intensity of the x-ray beam as it passes through the patient's tissue.
|
|
The x-ray photons are attenuated via what 2 processes?
|
Absorption and scattering
|
|
The amount of attenuation is dependent upon what factors?
|
*atomic number
*density of electrons
*thickness
*photon energy
|
|
The attenuation of an x-ray beam is highly dependent upon what?
|
The energy of the x-ray photons.
|
|
What is mA?
|
The tube current.
|
