Multi Slice CT Flashcards
-SSCT Slice thickness is defined by :
-MSCT slice thickness is defined by :
- collimation
- detector array
Pitch - SSCT
defined as
patient couch movement per rotation divided by the slice thickness.
SSCT the x-ray beam width=
slice thickness
A pitch < 1 leads
oversampling (double irradiation of some tissues)
- this means patient is moving faster than you are rotating around
EXAMPLE- TABLE MOTION = 2mm and SLICE THICKNESS =5mm
Pitch = 1
each slice is continuous
Pitch >1 implies
-gaps between the x-ray beams from adjacent rotations
-gaps get bigger between individual slices.
-tf lower image quality but lower dose
In MSCT “Beam Pitch” is defined
patient couch movement per rotation divided by the acquired length (ACQUISITION BEAM WIDTH)
For SSCT image noise depends on
-KV
-slice thickness
-mA
-Rotation time
Kv
↑kV = ↑ penetrating photons = more hitting the detector and less noise.
Slice thickness
-thicker slices=Detectors collect more photons(less noise)….produces more partial volume effect.
mA
↑mA= ↑higher photon flux tf less noise
Rotation time
faster rotation=shorter time acquiring photons tf more noise
Image noise is generally independent of
pitch
linear CT
CT rotates around 360º w patient moving.
the patients moves in a few mm for the next rotation
Heat loading
continous helical scanning increases the heat loading on the tube by 100.
causing a limiting factor
tf we need to produce tubes w better heat capacity
