Random Flashcards
“wasted radiation” that scatters beyond the edge of the detector rows:
overbeaming
irradiating tissue abaove and below the desired scan range found in helical scanning:
overRANGING
Pitch=
TFmmper36 degree rotation/number of detector rows *slice colimation in mm
what is the maximum pitch before data loss ocurrs:
2
Amathmatical formula used to convert scan data into image data:
reconstruction
Predetermined algorithms:
kernals
where are smooth kernels used:
brain or liver for low contrast detectability
where are sharp kernals used:
ases bone structures to increace spacial resolution
a post processing technique for off axis perspective of the original axial acuisition:
reformating
what post processing technique is used to make sagital and coronal iages:
reformated
contrast’s peak time for renal excreation:
3 min
urine iodine consitration is hightest at:
60min
what is an apropriate kVp for pediatric pts:
100
amount of radiation an individual is exposed to, not how much is absorbed:
a roentgen
measures the amount of radiation in the air:
roentgen
measures how much radiation is absobed:
Rad
describes the amount of radiation an individual is exposed to:
Rem
radiation absorbtion is measured in:
rad and rem
rem exposure
rad absorbed
measurment of radiation to specific tissue:
absorbed dose
units of absorbed dose:
gy
mGy
replaced the unit rem
measurement based on the sensitivity of the tissue exposed to radiation:
effective dose
effective dose is measured in:
sieverts
used to quantify the risks of developing cancer or genetic defects:
effective dose
measures radiation output from the scanner:
CTDI
a calculated value based on x-ray tube settings:
CTDIvol
a measurment of radiation to the scan volume of a phantom
CTDIvol
measurment of tube output based of kvp mas pitch and dose, estimates exposure per slice:
CTDIvol
measurment of total amount of exposure for a series of scans:
dose length profile
DLP=
CTDIvol * scan length
used to calculate efective dose for specific CT exams:
DLP
used to aproximate pt organ dose
CTDIvol
mAs per slice
Effective mAs
pixel size(mm^2)=
((dfov)(mm^2))/matrix size
voxel size=
(DVOF * slice thickness)/matrix size
ability to capture, absordb, and convert x-ray photons that have passed through a pt into an electical signal:
detecto/capture effciency
quantity of x-ray photons absorbed by th detectors.
absorbtion efficency
Ct detector output being proportional to photons capture:
linearity
slice thickness=
x-ray beam thickness/number of slices
allows the tech to interact with the imaging system
system console
process/convert the analog signal to digital by using the ADC:
host computer
what is located in the gantry: (6)
x-ray tube
slip ring
generator
collimator
detectors
DAS
reconstructs attenuated raw data into a CT image
array processor
quantity of x-radiation passing through a uniy area:
photon fluence
major diadvantage of back projection:
star artifact
the amount of enerrgy that passes through the PT onto the detector:
transmited intensity
limiting resolution f modern scanners:
25lp/cm
the distance between the centers of two adjacent reconstructed CT images:
section interval
