CT scan Generations (GEN 1-7 Flashcards
*Original EMI Scanner
*Designedfor neurologic examination only
*A demonstration project
*EMI Ltd.
*Very long scan times
*No longer in use
FIRST GENERATION
Translate-rotate (scan-index)
*180 translations, 1o rotation
*Pencil x-ray beam (3x26 mm
field)
*Single or paired detectors (NaI)
FIRST GENERATION
5 mins scan time
*Uses water bag
*Eliminates air interfaces
*Has reference detector
*Help to calibrate
*Reduce artifacts
FIRST GENERATION
FIRST GENERATION Brain tissue scanner matrix?
80 x 80 matrix
Permits whole body exam
*No longer available
2nd
*Increased radiation intensity that
occurs toward the edges of the beam
*Long examination time
*For one complete examination
*Increased scatter radiation
*Due to loss of collimation
SECOND GENERATION
*Translate-rotate
*18/6 translations, 10o/30o rotations
*Narrow fan x-ray beam
*Multiple detector (5-30)
*30 secs scan time
SECOND GENERATION
*Most widely used generation
*Rotate only system
*De facto baseline model
THIRD GENERATION
Rotate-rotate
*Subsecond scan time (<100 ms)
*Curvilinear (30-60o) detector
array (250-750 detectors)
*Wider fan x-ray beam
*Reference detector
*Measures beam
*700,000 measurements/sec
*220o or 360o scanning arc
*Reduced scan time (1-10 secs/slice)
THIRD GENERATION
Advantages:
*Tube directly focused on the detector array
*Good image reconstruction
*Better collimation
*Reduces scatter radiation
*Improve image quality
*Prevents motion artifacts
THIRD GENERATION
*Disadvantages:
*Prone to ring artifacts
*Detector malfunction
*Compensation:
*Software connected image reconstruction
algorithm
*Recalibration
THIRD GENERATION
Closer SID
*Lower technical factors
*Dynamic (15 scanning sections/min)
*Uses over scan
*Tube arc >360o
*1,200,000
measurements/section
*Rotate-stationary
*Wide fan beam
*Stationary/fixed detector array (360o
detector ring)
*600-2000 detectors
*4800 detectors
*Subsecond scan time
FOURTH GENERATION
Advantage:
*Free of ring artifacts (auto- detector
calibration)
*Disadvantages:
*Interscan time
*Computer processing time
*Increased patient dose
*Motion artifact
*High cost
FOURTH GENERATION
Electron Beam or Cardiac Cine or Ultrafast CT
*Dedicated cardiac unit designed
*Produced by Imatron (1980)
*50 ms scan time
*Uses huge electron gun
*Rotating electron beam
*Uses deflection coil
*Direct the 30o beam of electron in a 210o arc
*Dynamic imaging (4 sections/50ms)
*Annular/Semicirculartargets
FIFTH GENERATION
Helical/Spiral CT
*Volumetric scanners Continuous data
acquisition scanning
*Uninterrupted table movement
*Introduced by Will Kalender and Kazuhiro Katada
*Reconstruction is possible at any desired z-axis
position
*Uses slip ring technology
*Eliminated interscan delay
*Made helical CT possible
SIXTH GENERATION
*Eliminates overlap and missed areas Due to breathing
*Reduces motion artifacts
*Respiratory & cardiac
*Pitch settings can be set to oversample
sections of interest
SIXTH GENERATION
*Advantages:
*Beneficial to patient comfort
*Beneficial to department productivity
*Superior MPR & 3D reformation
SIXTH GENERATION
Disadvantages: *Full 360o projection data is not
acquired for each section *The patient is continuously advancing
through the gantry bore during the exposure
*Section are reconstructed to
represent approximate acquisition of planar data
SIXTH GENERATION
Applications:
*CT angiography
*Radiation therapy treatment planning
*Imaging uncooperative patients
SIXTH GENERATION
Multisection CT (MSCT)
*Multidetector CT (MDCT)
*Multidetector Array Scanners (MDA)
*Produces multiple slices in a single rotation
*16,32,64,128, 256-section scanner
SEVENTH GENERATION
determined by the
width of the detector
MDCT Section Thickness
determined by the
collimator size
*SDCT Section Thickness
Provides longer & faster z axis
coverage/gantry rotation
*Increased volume coverage/unit time
*Dramatically reduces total examination time
*Combined with helical scanning
SEVENTH GENERATION
Advantages:
*More efficient
*Reduces patient exposure
*Allows post-acquisition reconstruction
*Increases image resolution
*Section thickness can be reduced
Axial data acquisition
*Used when speed is not a major concern
*Used when optimal resolution is required
e.g. IAC
*Helical data acquisition
SEVENTH GENERATION
