There are 7 generations of CT scanners that have advanced over time to provide faster acquisition times, better spatial resolution, and shorter reconstruction times. The document describes each generation's key features and advantages/disadvantages. First generation used a pencil beam and translate-rotate motion. Later generations introduced fan beams, complete rotation, ring detectors, and dual x-ray sources to improve imaging capabilities while reducing motion artifacts and scan times. The latest generations aim to differentiate tissue composition using dual-energy techniques.

1. GENERATIONS OF CT
BY: Ms. Mamta Panda

2. GENERATIONS OF CT MACHINES
First Generation Pencil Beam; Translate- Rotate Motion
Second Generation Narrow Fan Beam; Translate- Rotate Motion
Third Generation Wide Fan Beam; Complete Rotation Motion
Fourth Generation Ring Detector; Complete Rotation Motion
Fifth Generation Electron Beam Scan; Dynamic Spatial Reconstruction
Sixth Generation Dual Source ; Dual Multi Detector
Seventh Generation Flat Panel Digital Area Detector
Changes and advances according to time in CT scanner.
There are 7 generations of CT scanner-

3. AIM
Provide faster
acquisition time
Better spatial
resolution
Shorter
computer
reconstruction
time
Simplification of
mechanical
motion

4. FIRST-GENERATION SCANNERS
• Parallel beam geometry was first used by Hounsfield (1973). The first EMI
brain scanner and other earlier scanners were based on this concept.
• Parallel beam geometry is defined by a set of parallel rays that generates a
projection profile (Fig. 4-2).
• The data acquisition process is based on a translate-rotate principle, in which
a single, highly collimated x-ray beam and one or two detectors first translate
across the patient to collect transmission readings.
• After one translation, the tube and detector rotate by 1 degree and translate
again to collect readings from a different direction.
• This is repeated for 180 degrees around the patient. This method of scanning
is referred to as rectilinear pencil beam scanning.
• First-generation CT scanners took at least 4.5 to 5.5 minutes to produce a
complete scan of the patient, which restricted patient throughput.
• The image reconstruction algorithm for first-generation CT scanners was based
on the parallel beam geometry of the image reconstruction space (a square or
circle in which the slice to be reconstructed must be positioned).

8. ADVANTAGES :
• Pencil beam geometry allowed very efficient scatter reduction.
DISADVANTAGES:
• NaI is Hygroscopic (absorb moisture from air)
• High scan time
• Complex mechanical motion of rotate-translate system
• Poor spatial resolution
• Shorter rotational angle
• Design only for head

9. SECOND-GENERATION SCANNERS
• Second-generation scanners were based on the translate-rotate principle of first-generation scanners with a
few fundamental differences, such as a linear detector array (about 30 detectors) coupled to the x-ray tube
and multiple pencil beams.
• The result is a beam geometry that describes a small fan whose apex originates at the x-ray tube. This is the
fan beam geometry shown in Figure 4-3, B, C, and D.
• Also, the rays are divergent instead of parallel, resulting in a significant change in the image reconstruction
algorithm, which must be capable of handling projection data from the fan beam geometry.
• In second-generation scanners, the fan beam translates across the patient to collect a set of transmission
readings.
• After one translation, the tube and detector array rotate by larger increments (compared with first-generation
scanners) and translate again.
• This process is repeated for 180 degrees and is referred to as rectilinear multiple pencil beam scanning.
• The x-ray tube traces a semicircular path during scanning. The larger rotational increments and increased
number of detectors result in shorter scan times that range from 20 seconds to 3.5 minutes.
• In general, the time decrease is inversely proportional to the number of detectors. The more detectors, the
shorter is the total scan time.
• Bowtie filter was firstly used in this generation.

12. ADVANTAGES
• Shorter scan time
• Speed increased of scanning due to increased number of detector
• Larger rotational increments
DISADVANTAGES
• More scattered radiation
• Hygroscopic nature of NaI
• Complex mechanical motion of translate rotate
• Scatter radiation increased due to narrow fan beam

13. THIRD-GENERATION SCANNERS
• Third-generation CT scanners were based on a fan beam geometry that rotates
continuously around the patient for 360 degrees.
• Up to about 750 detectors were used in this generation.
• Both Xenon and scintillator detectors were used
• The x-ray tube is coupled to a curved detector array that subtends an arc of 30 to 40
degrees or greater from the apex of the fan.
• As the x-ray tube and detectors rotate (rotate-rotate principle), projection profiles are
collected and a view is obtained for every fixed point of the tube and detector.
• This motion is referred to as continuously rotating fan beam scanning. The path traced
by the tube describes a circle rather than the semicircle characteristic of first- and
second-generation CT scanners.
• Third-generation CT scanners collect data faster than the previous units (generally within
a few seconds).
• This scan time increases patient throughput and limits the production of artifacts caused
by respiratory motion.
• This is the most commonly used method today and takes about 0.3 seconds to image a
single slice

15. ADVANTAGES
• Improvement in detector and data acquisition technology
• Shorter scan time
• High spatial resolution
• Patient dose less
DISADVANTAGES
• Ring artifact
• Expensive
• More scattered radiation due to wide angle fan beam
• Complex electronic circuitry

16. RING ARTIFACT
• It is never possible to have a large number of detectors in perfect balance with each other during continuous
rotation of source detector assembly
• If one of the detectors is out of calibration, the detectors will give a consistently erroneous reading at each
angular position, resulting in a circular artifact called as ring artifact.
• So, ring artifact occurs due to miscalibration or failure of one or more detector elements

17. FOURTH-GENERATION SCANNERS
• Essentially, fourth-generation CT scanners feature two types of beam geometries: a rotating fan beam
within a stationary ring of detectors and a nutating fan beam in which the apex of the fan (x-ray tube)
is located outside a nutating ring of detectors.
• It was rotate/ stationary system with wide fan beam
• Huge no. of detectors (up to 4,800) were used
• This generation was designed to overcome the ring artifact

18. Rotating Fan Beam Within a Circular Detector Array
The main data acquisition features of a fourth generation CT scanner are as
follows:
1. The x-ray tube is positioned within a stationary, circular detector array.
2. The beam geometry describes a wide fan.
3. The apex of the fan now originates at each detector. Figure 4-4 shows two fans
that describe two sets of views.
4. As the tube moves from point to point within the circle, single rays strike a
detector. These rays are produced sequentially during the point’s circular travel.
5. Scan times are very short and vary from scanner to scanner, depending on the
manufacturer.
6. The x-ray tube traces a circular path.
7. The image reconstruction algorithm is for a fan beam geometry in which the
apex of the fan is now at the detector, as opposed to the x-ray tube in the third-
generation systems.

19. Rotating Fan Beam Outside a Nutating Detector Ring
In this scheme,
The x-ray tube rotates outside the detector ring.
As it rotates, the detector ring tilts so that the fan beam strikes an array of
detectors located at the far side of the x-ray tube while the detectors
closest to the x-ray tube move out of the path of the x-ray beam.
The term nutating describes the tilting action of the detector ring during
data collection.
Scanners with this type of scanning motion eliminate the poor geometry
of other schemes, in which the tube rotates inside its detector ring, near
the object.
However, nutate-rotate systems are not currently manufactured.

21. ADVANTAGE-
• Reduced ring artifact
• Reduced motion artifact
• No complex electronic circuitry
DISADVANTAGE-
• Higher patient dose
• Higher cost
• More sensitive to scattered radiation than 3rd generation

23. MULTISLICE CT SCANNERS: CT SCANNING IN
SPIRAL-HELICAL GEOMETRY
Helical ("spiral") CT image acquisition was a major
advance on the earlier stepwise ("stop and shoot")

24. Helical CT scanner acquire data while the table is moving.
Raw data from helical scan can be interpolated to approximate acquisition of planar reconstruction data, by
interpolation algorithm.
Image reformatting is possible to display coronal, sagittal or oblique views.
Collimator pitch= Table movement per 360 degree rotation
Collimator width at isocenter
This pitch influences radiation dose, image quality and scan time.
 If pitch = 1 Normal scanning.
 If pitch > 1 table motion faster under scanning.
 If pitch < 1 table motion slow over scanning.
Image quality increases with patient dose increment.
(use for pediatric patient image quality decreases and
patient dose is also reduced )

25. Advantages-
• No motion artifact.
• High quality reconstruction.
• Reduce scan time.
• Smooth movement of gantry and other components.
Disadvantages-
• More processing time.
• Expensive.
• Tube heating increased.
• Reduced resolution.

26. Axial vs spiral scanning
“Step and shoot”
1.Gantry stops and rotates to acquire data from single
slice
2.X-rays switched off
3.Patient moves to next slice
4.Rotates to acquire data from next slice

27. •Gantry keeps rotating continuously releasing x-ray beams.
•The couch simultaneously moves.
•This results in a continuous spiral scanning pattern.
Advantages:
•Avoids respiratory misregistration as scan performed
during one breath
•More effective use of contrast agent as faster scanning
enables scanning during multiple phases in one contrast
injection e.g. portal venous, angiographic, delayed
•Overlapping slices allows better reconstruction and helps
in showing smaller lesions
•Pitch > 1 can be used to reduce scan time and / or
radiation dose and still cover the same volume

28. Multi-slice CT Scan (MSCT) OR Multi- Detector Ct Scan (MDCT)
• This generation CT uses 3RD generation CT with helical scanning and low voltages
slip rings.
• In MSCT, the multiple rows of detectors are used instead of using only one row of
detector as previous generations.
• The multiple rows of detectors allows for registration of more than one channel per
gantry rotation.
• Multislice scanning uses lots of rows and each row consists of equal-sized
detectors
• Rows combined to give different number of slices. Number of slices limited by
number of data channels.
Older scanners may use one of the following types of detector array:
• Linear array: all detector rows are of equal width
• Adaptive array: detector rows are of different widths
• Hybrid array: central rows narrower than outer rows. Most commonly used
array today.

29. The elements within the central detector rows are the
thinnest and they get wider towards the outside.
Advantages:
• As few detector elements as possible
activated to still give a large range of
detector slices
• Fewer detector rows activated means fewer
septae dividing up the rows. This improves
the dose efficiency.
Disadvantage:
• Upgrading to more data channels requires an
expensive detector replacement.

30. •Similar to linear arrays in that the elements within the detector rows are the same width
across. However, the central group of detector rows are narrower than the outer rows.
•These are the main detector arrays used for 16-slice scanners and above.

31. Other main features of MSCT
• Cone shaped beam is used.
• Slip ring technology used.
• Collimator spacing is wider.
• Slice thickness is controlled by detector size, not by
the collimator.

32. • Detector pitch-
Table movement per 360 degree rotation of gantry
Detector width
• Relation b/w detector pitch and collimator pitch-
Collimator Pitch = Detector Pitch
N
N= No. of detector array in MSCT

33. PITCH

34. ADVANTAGES-
• Faster acquisition.
• Reduced scanning time.
• High resolution images.
• Ultra thin slices
• Lesser contrast agent
DISADVANTAGES-
• High radiation dose.
• Very expensive equipment.
• Data overload.

35. SLIP-RING TECHNOLOGY
• In conventional CT scanning there was paused between each gantry rotation.
• But in helical CT, slip ring technology is used which allows continuous rotation
of gantry without interruption.
• Spiral-helical CT is made possible through the use of slip-ring technology,
which allows for continuous gantry rotation.
• Slip rings (Fig. 4-11) are “electromechanical devices consisting of circular
electrical conductive rings and brushes that transmit electrical energy across a
rotating interface” (Brunnett et al., 1990).
• Today, CT scanners incorporate slip-ring design and are referred to as
continuous rotation, volume CT, or slip-ring scanners.

36. Slip-ring functions to allow the transfer of electrical information and power between a rotating device and
external components. They are used in helical CT and MRI scanners among other applications; in this setting,
they allow image acquisition without progressive twisting of cables as the scanner rotates
A rotating circular conductor as opposed to a nonrotating conductive metallic strip to allow a complete circuit to
be maintained despite device rotation.
Specific functions of slip rings include:
• Transferring high voltage to power the rotating device
• Transferring information to the rotating device (for example from a CT control room to the CT scanner)
• Transferring information from the rotating device (for example from a CT detector array)

37. FIFTH-GENERATION SCANNERS
ELECTRON BEAM CT SCANNER
Fifth-generation scanners are classified as high-speed CT scanners
because they can acquire scan data in milliseconds.
The principles and operation of the EBCT scanner were first
described by Boyd et al. (1979) as a result of research done at the
University of California at San Francisco during the late 1970s.
In 1983, Imatron developed Boyd’s high-speed CT scanner for
imaging the heart and circulation (Boyd & Lipton, 1983).
At that time, the machine was referred to by such names as the
cardiovascular computed tomography scanner and the cine CT
scanner. Today, the machine is known as the EBCT scanner
It is expected that more of these machines will be distributed
worldwide in the near future. (Siemens Medical Systems will
distribute the EBCT scanner under the name “Evolution.”)

38. • The overall goal of the EBCT scanner is to produce high-
resolution images of moving organs (e.g., the heart) that are
free of artifacts caused by motion.
• In this respect, the scanner can be used for imaging the
heart and other body parts in both adults and children. The
scanner performs this task well because its design enables it
to acquire CT data 10 times faster than conventional CT
scanners.
The design configuration of the EBCT scanner (Fig. 4-8) is
different from that of conventional CT systems in the
following respects:
1. The EBCT scanner is based on electron-beam technology
and no x-ray tube is used.
2. There is no mechanical motion of the components.
3. The acquisition geometry of the EBCT scanner is
fundamentally different compared with those of
conventional systems.

39. At one end of the scanner is an electron gun that generates a 130-kilovolt (kV) electron beam.
This beam is accelerated, focused, and deflected at a prescribed angle by electromagnetic coils to strike
one of the four adjacent tungsten target rings.
These stationary rings span an arc of 210 degrees (tungsten).
The electron beam is steered along the rings, which can be used individually or in any sequence.
As a result, heat dissipation does not pose a problem as it does in conventional CT systems.
When the electron beam collides with the tungsten target, x rays are produced.
Collimators shape the x rays into a fan beam that passes through the patient, who is positioned in a 47-cm
scan field, to strike a curved, stationary array of detectors positioned opposite the target rings.
The detector array consists of two separate rings holding a 216-degree arc of detectors.
The first ring holds 864 detectors, each half the size of those in the second ring, which holds 432 detectors.
This arrangement allows for the acquisition of either two image slices when one target ring is used or eight
image slices when all four target rings are used in sequence.
Each solid-state detector consists of a luminescent crystal and cadmium tungstate (which converts x rays to
light) coupled optically with silicon photodiodes (which convert light into current) connected to a preamplifier.
The output from the detectors is sent to the data acquisition system.

40. ADVANTAGE-
• It can produce fast frame rate
• Minimum motion artifact
• No complex electronic circuitry
• Increased speed
DISADVANTAGE-
• Higher patient dose
• Higher cost
• More sensitive to scattered radiation than 3rd generation

41. SIXTH-GENERATION SCANNERS:
THE DUAL-SOURCE CT SCANNER
This is the new technology of CT scan that uses two x-ray photon spectrum to create images
Aim :-
Differentiation and classification of tissue composition.
Principle:-
Material separation of different composition is achieved with DECT.
• CT number at each voxel can be compared with different energies.
• Linear attenuation co-efficient of different element will be different so that unique absorption properties of
two material permits their material classification.

42. METHOD OF OBTAINING DECT
A. Single source with fast Kv switching:-
Single x-ray source is used with fast switching b/w 80-140 KVp
generates two energy x-ray spectrum.
Tube current is not varied.
65% exposure time used for 80 Kv acquisition and 35% exposure time
used for 140 kv acquisition.
Rapid peak kilovoltage (kVp)
switching CT.

43. B. Single source with dual detector array:-
In this method also single x-ray source is used but modified detector array used with two scintillation layer
arranged, one top of other to receive separate high and low energy data from x-ray source.
Top detector layer captures low energy data
Bottom detector layer captures high energy data
Dual-layer CT. CT

44. C. Dual source with dual detector array
In this method two x-Ray tubes are used with two detector
arrays.
The both x-Ray tubes and detectors are orthogonal (90 degree
angle) to each other
They acquire tow different image data simultaneously
Two different x-Ray tubes allow filtration and tube current
adjustment to optimal image quality
The size of detector is always smaller than first detector

46. SEVENTH-GENERATION SCANNERS:
FLAT-PANEL CT SCANNERS
Flat-panel digital detectors similar to the ones used in digital radiography are
now being considered for use in CT; however, these scanners are still in the
prototype development and are not available for use in clinical imaging.
A flat-panel CT scanner prototype is shown in Figure 4-10. The x-ray tube and
detectors are coupled and positioned in the CT gantry.
The detector consists of a cesium iodide (CsI) scintillator coupled to an
amorphous, silicon thin-film transistor array.
These flat-panel detectors produce excellent spatial resolution but lack good
contrast resolution; therefore, they are also used in angiography to image blood
vessels, for example, where the image sharpness is of primary importance.
In addition, flat-panel detectors are also being investigated for use in CT of the
breast, and currently several dedicated breast CT prototypes are being
developed

47. IMPROVEMENT
• 1989- Spiral CT
 Rotation And Patient Motion
 Scan In Single Breath Hold
 1mm- 10mm Slice Thickness
• 1991- Dual Spiral
• 2003- 64 Multislice CT
 Single Scan In 0.33sec
 Entire Scan In 20-60 Sec
 Resolution- 0.4mm
 512* 512 Images
• 2007-256 Multislice CT

48. ADVANCEMENT
Detector
X-ray tube
Gantry rotation
DECT
Different technique
PET–CT
Portable CT

49. ADVANCEMENT IN DETECTORS
• Ultrafast ceramic (UFC)
• Stellar
• Gemstone

50. ADVANCEMENT IN CT TUBE
• Straton tube
• Maximum rotalix ceramic x-ray tube (MRC)
• Liquid metal anode x-ray tube (LIMAX)
• Aquillion one x-ray tube.

51. GANTRY ROTATION TIME
 Rotation time is the time interval needed for a complete 360 degree rotation of the tube and the detector
system around the patient.
 Advantages of shorter scan time:
• Longer spiral length can be acquired in the same time.
• Same volume and same slice thickness can be scanned in less time.
• Increased temporal resolution.
• Motion artifacts are reduced.

52. BY: Ms. Mamta Panda
mpanda483@gmail.com