CT- SCANNING SYSTEM

1. GENERATIONS OF CT SCANNER
MACHINE
• WAQAS MAHMOOD
23-FA-00675

2. CT- SCANNING SYSTEM
• First Generation-Parallel Beam Geometry.
• Second Generation-Fan Beam,Multiple Detectors.
• Third Generation-Fan Beam,Rotating Detectors.
• Fourth Generation-Fan beam,Fixed Detectors.
• Fifth Generation-Scanning Electron Beam.
• Spiral/Helical Scanning

3. FIRST GENERATION CT
• To Acquire a projection (X-ray)
translation and rotation motion is
used
• Translate x-ray pencil beam and
detector across body and record
output(eg.160 measurements)
• Translational scanning seperated
by 1 degree increments repeated
thro arc of 180 degree.
• Assemble all the projections.
• Typical scan time of 5 minutes.
• Limited only to brain studies.

6. 1st Generation Data Collection

7. Hounsfield’s CT Formulation
• Measurement Ni
written as sum of
attenuation of
pixel along path
• Solve simultan-
eous equations
from data at many
positions and
angles

8. Second generation scanners
• Fan shaped beams where introduced so that multiple measures are made simultaneously
• Fan-shaped beam & increased number of detectors permitted scanning and rotation with fewer
linear movements (eg. 30 degree fan beam and 10 degree angular increments.)
• Improved image quality by reducing the effects of motion
• Loss of collimation increased the amount of scatter detected = major disadvantage
• Long data reconstruction time.
• Scan time – 20 to 60 seconds
• Reasonable breath holds
• Exams of whole body now possible

11. Third Generation
• Wider fan-shaped beam
• Curved array of 250 - 750 detectors to
achieve a single projection
• Beam was wide enough to include entire body
in a single exposure
• Complete 360 degree rotation Rotate/Rotate
movement
• One rotation = one slice
• Second data acquisition could be made as the
tube and detectors move in the opposite
direction.
• Time reduced to 1 sec per slice
• Dynamic scanning – 4 scans per minute

12. THIRD GENERATION CT (Contd..)

14. FOURTH GENERATION CT

15. Fourth generation CT
• Single-projection fan-shaped beam
• 600-2000 stationary detectors in a 360° ring
• Wider range of scan arcs possible with scan times from 0.5
– 10 seconds
• Some are capable of scan rates of 15 scans per minute
• Limiting factor = interscan time & computer processing
time

17. 1ST, 2ND, 3RD, & 4TH GENERATION
One detector
Translation-rotation
Parallel-beam
Multiple detectors
Translation-rotation
Small fan-beam
Multiple detectors
Translation-rotation
Large fan-beam
Detector ring
Source-rotation
Large fan-beam
1st Generation 2nd
Generation
3d Generation
4th
Generation
YUMC RIRS

18. FIFTH GENERATION CT SCANNER
(OR) ULTRA FAST CT SCANNER
• ELECTRON BEAM COMPUTED
TOMOGRAPHY or CARDIAC CINE
• X-ray tube is replaced with an
electron gun
• Deflection coil to direct electron
beam around an anode ring
• Uses an electron beam accelerated by
130-140KV instead of x-ray tube.
• Focal point is Electromagnetically
focused around the patient,deflected
over target in 50 ms scan times.
• Used in cardiac examinations.
• 4 anode rings, 2 detector rings,8
contiguous slices,8x8 mm scanned
area.
• Heartscan by Imatron EBCT

21. WILLI KALENDER Developed Spiral CT in 1989
SPIRAL (HELICAL) CT

22. SPIRAL (HELICAL) CT
• Referred to as Helix, volume or 3 D CT Scanning.
• If the X Ray tube can rotate constantly, the patient can then be moved continuously through the
beam, making the examination much faster
• For helical scanners to work, the X Ray tube must rotate continuously
• This is obviously not possible with a cable combining all electrical sources and signals
• A self lubrication “Slip Ring” is used to supply power and to collect the signals

23. HELICAL SCAN PRINCIPLE
• Scanning Geometry
• Continuous Data Acquisition and Table Feed
X Ray beam
Direction of patient
movement

24. • Helical (spiral) Scanners
• Slip ring technology
• Current and voltage supplied while the tube is in continuous motion around the gantry
• Table is moved slowly during exposure while tube is in continuous rotation.
• Scanning motion has a set circular diameter (helix)
• Much shorter scan time = 30-40 seconds for entire abdomen
• Less contrast is needed
• Entire exam can be completed in 1 breath hold
• Eliminates overlaps & variations in inspirations
• Reduces possibility of motion artifacts
• Primary disadvantage: a full 360 set of data is not acquired for each section
• The patient is continually advanced through the gantry during exposure
• Sectional image is created from computer reconstructions

25. A LOOK INSIDE A SLIP RING CT
X Ray
Tube
Detector
Array
Slip Ring
Note:
how most
of the
electronics
is
placed on
the rotating
gantry

28. SPIRAL (HELICAL) CT
• A pitch of 1 yields contiguous spiral.
• A pitch of 2 yields an extended spiral.
• A pitch of ½ yields an overlapping spiral.

29. SPIRAL (HELICAL) CT vs. CONVENTIONALCT
• Fasterimage acquisition
• Quicker responsd to contrast medium
• Fewer motion artifactrs
• Improved two-axis resolution
• Physiological imaging
• Improved coronal, sagittal, and 3D imaging
• Less partial volume artifact.
• Ability to set pitch at less than 1.0 and produce oversampling of areas of interest
• Image reconstruction can be set for smaller section thicknesses than those that were acquired.
• Increasing pitch value permits a greater field of view to be imaged in a shorter time.
• Using the smallest detector size combined with a pitch of less than 1 increases resolution in the z plane

30. SINGLE-SLICE VS. MULTI-SLICE
DETECTORS

31. SINGLE-SLICE CT
1sec/revolution

32. 7th Generation(Multi slice)
• Single slice CT scanners:
• Section thickness
determined by collimator
size
• Multi Slice CT scanners:
• Section thickness is
determined by the width of
the detector
• Resolution is determined
by the width of the
detector

33. MSCT

34. HELICAL MULTI-SLICE CT
16 SLICES
0.4 sec/revolution
1.25 slice thickness
1000 images/whole body study

35. MSCT
• Because these bands of detectors operate simultaneously – a single beam
exposure can produce multiple sets of image receptor data.
• When combined with helical scanning:
Total exam time is dramatically reduced
(chest or abd procedure: 15-20 sec).
• Section thickness determined by collimator size in single slice.
• Section thickness is determined by the width of the detector and resolution
determined by width of detector in multi slice detector.

36. 7th Generation
• MSCT:
• More efficient
• Reduces patient exposure
• Increases image resolution
• Allows post-acquisition reconstruction at new levels…

37. 7th
• Example:
• 20 mm collimated beam width can expose an array of four 5 mm detector
bands – the dataset from this exposure can be displayed as:
• Four 5 mm sections
• Two 10 mm sections
• One 20 mm section
• Any other combination = unlimited choices for Dr