CT GENERATIONS COMPARISON

	3rd Generation	4th Generation	5th Generation	6th Generation	7th Generation
Geometry	Rotate-Rotate	Rotate-Stationary	Stationary-Stationary - Imatron electron beam scanner	Rotate-Rotate Helical CT	Multiple detector array CT - rotate rotate geometry
X-ray Tube	Rotating Tube 360 degree and then reverse	Rotating tube 360 degree and reverse	Large arc of tungsten encircles patient and lies opposite detector ring	Slip ring technology allow continuous movement around gantry	Slip rings allow continuous movement around gantry
Beam	Wide Beam to form an arc over patient	Wide Beam to form an arc over patient	X-rays produced from focal track as high energy electron beam strikes tungsten - electron beam produced in a cone like structure is electronically steered around the patient	X-ray beam moves in helical pattern	Wide beam
Detectors	Rotating array of detectors rotating with rotating x-ray tube in Gantry (800)	Stationary ring of detectors (4800+)	Beam on High voltage target ring that covers a 210 degree arc		512 slice (new 640 slice MDCT), Detector array closely abutted
Detector type	Xenon gas (25 atm) or Solid State	Solid State	Solid State	Solid State	Solid State
Fan Beam Geometry	Source fan - x-ray tube apex	Detector Fan - detector apex
Reference beam measured by	detectors near the edge of the detector array	measured by same detector used for transmission measurement
Slice thickness determined by	Collimator	Collimator	Collimator	Collimator	Slice thickness limited by detector size, increased by binning different # of detector subunits together and moving collimator to the edge of all 4 slices
Collimator < detector size	Yes	Yes	Yes	Yes	Collimator space 4x > detector array size
Acquisition				Acquire data while table is moving. Interpolation of helical data set. Interleaving reconstruction (<2:1 clinical limitation).
Movement artefact	More	more	None	Single breath hold for entire abdomen <30s	Reduce patient movement - acquisition in single breath hold
Helical Pitch				Collimator pitch = table movement / collimator width	Detector pitch = table movement / detector width
Other	Ring Artifact from detector failure		No Moving Parts Cine CT Cardiac imaging	Use less contrast. Increase patient throughput	3D images, CT Angiograms and even Image beating heart
Speed	<5s / slice	<2s / slice	<50 us	30s / abdomen series	<0.4 s
Filter	Bow-tie	Bow-tie
Slice sensitivity profile				Slightly Broader