Week 13 - Dose Flashcards
What happens to dose when the CT diameter gets smaller?
Dose increases
*larger diameter, lower dose
T/F
As the CT diameter increases, image quality declines and noise is increased
True
Where is dose the least within the slice?
The center
Where is dose the most in a slice?
Outside the center, will vary with body dimension, composition and MA modulation
What are 4 types of dosimeters?
-film dosimeter
-thermoluminescent dosimeter (TLD)
-pencil ionization chamber
-solid state metal oxide semiconductor field effect transistor (MOSFET)
A ratio of the distance the table travels per revolution to the total nominal beam collimation
CT dose index (CTDI) pitch
What 2 dose metrics are used to document dose after CT scan?
CTDI
dose length product (DLP)
T/F
The weighting for CTDI is less in the center than the periphery
True
-developed by the IS food and drug administration (FDA)
-represents the mean absorbed dose in the scanned object volume
-unit of measurement is Gray (Gy)
CT dose index
T/F
CTDIw accounts for the average dose in the x-y axis of the patient instead of the z -axis
True
T/F
CTDIvolume considers the dose in the z-axis
True
Provides a measurement of the exposure per slice of tissue
CTDIvolume
Provides a measurement of the total amount of exposure for a series of scans
DLP
*calculates total energy imparted to a patient
-the selection of milliamperage and time before scan begins
-determines quantity of photons (dose) incident on the patient for the duration of the exposure
-dose is directly proportional to mAs
Constant mAs
Term used for multislice CT scanners that denotes the mAs per slice, creating a relationship with pitch
Effective mAs
*effective mAs = true mAs / pitch
-penetrating power of the photons coming from the xray tube
*radiation dose is proportional to the square of the kvp
Peak kVp
T/F
Multidector CT has a higher dose profile than single detector
True
