The document discusses advances in computed tomography (CT) scanning technology. It describes the development of helical/spiral CT scanning using slip ring technology in the 1990s, allowing for continuous tube rotation. It then outlines the progression of multidetector CT (MDCT) from dual to 64+ slices, enabled by advances in detector arrays. MDCT provides improvements like faster scanning, thinner slices, reduced motion artifacts, and longer anatomical coverage. The document also reviews developments in CT tubes, reconstruction techniques, post-processing methods, and dual-source CT configurations.

1. Advances in CT
Sahara Mahato
Roll no – 96
B. sc.mit 2nd year
1
Advancement in CT

2. Outline
• Introduction
• Historical aspects
• Helical CT
• Multi detector CT
• Advantages
• Post processing technique
• Conclusions
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3. Introduction of CT
• CT is an imaging technique introduced in the
early 1970s that generates cross-sectional
images in the axial plane.
• The first CT Scanner was developed by
GODFREY HOUNSFIELD in 1972.
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Advancement in CT

4. History of CT
• In 1972, the first CT scan was introduced by
EMI.
• In 1990, the single slice helical/spiral CT was
introduced by Toshiba.
• 1n 1992, dual slices CT was introduced by
General Electric.
• In 1995, CT fluoroscopy was introduced by
Toshiba.
• 1n 1998, 4 slices MDCT was introduced.
Advancement in CT 4

5. Contd…
• In 2001, 8 slices MDCT was introduced.
• 1n 2002, 16 slices MDCT was introduced.
• In 2004, 64 slices MDCT was introduced.
• In 2005, dual source CT was introduced by
Siemens.
Advancement in CT 5

6. Contd…….
• In 2006, 256 slices MDCT was introduced by
GE.
• In 2008, 320 slices MDCT was introduced by
Toshiba.
• In 2010, 640 slices MDCT was introduced by
Toshiba.
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7. Advances in CT
• First - Helical CT
• Second - Multidetector CT/ Multi row CT
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8. Single slice Helical CT
• In 1990, the first single slice helical CT was
introduced by Toshiba.
• Generation wise, it was fifth generation CT.
• In helical CT, the patient table translates
through the gantry while the x-ray tube and
detector rotates continuously around the
patient, creating a volume of data.
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9. Contd……
• Once a volume of data is collected, an image
can be reconstructed at any point along the
effective path traced by the x-ray tube.
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Z-AXIS

10. Contd……
• The helical scanning in CT was possible due to
the Slip Ring Technology.
• In this CT, one slice per gantry rotation is
obtained.
• Single row of detectors is used.
• Can acquire data fast as compare to
conventional CT.
Advancement in CT 10

11. Pitch
• Pitch is defined as the ratio of
table increment per 360 degree
gantry rotation over slice
thickness.
• Pitch <1 results in overlapping
images and increased patient
dose.
• Pitch >1 results in extended
imaging and reduced patient
dose.
Advancement in CT 11

12. Slip Ring Technology
• Slip rings are
electromechanical
conducting brushes
that transmits power
to gantry
components for its
continuous rotation.
• Due to the slip ring
technology, helical
scanning is possible.
Advancement in CT 12

13. Contd….
• One surface is a smooth ring and other a ring
with brushes that sweep the smooth ring.
• In a slip ring gantry system, power and
electrical signals are transmitted through
stationary rings within the gantry.
• Thus eliminating the need for electrical cables.
Advancement in CT 13

14. Contd….
• Brushes that transmit power to the gantry
components glide in contact grooves on the
stationary slip ring.
• Composite brushes made from conductive
material(silver graphite alloy) are used as a
sliding contact.
• Slip rings are drum or annulus shaped.
Advancement in CT 14

15. Contd…..
• There are usually 3 slip-
rings in a gantry.
– One provides high voltage
power to a x-ray tube and
generator.
– Second provides low
voltage power to control
system on rotating gantry.
– Third transfers digital data
from the detectors ( data
acquisition ).
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16. Advantages of helical over
Conventional CT
• Large volume coverage in single breathe hold.
• High speed
• Improved detection of small lesions
• Improved contrast enhancement
• Image reconstruction and manipulation
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17. Multidetector CT
• MDCT represents the latest breakthrough in
CT technology .Generation wise- seventh
• It is a specialized CT system equipped with a
multi detector array that simultaneously
obtains data at diff slices (4, 16, 64, 128, 256,
320 and 640) during one gantry rotation.
• The primary difference between single-slice
CT (SSCT) and MDCT hardware is in the design
of the detector arrays.
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18. MDCT has following features
• Multiple Detector rows .
• DAS(Multiple).
• Faster Gantry rotation(sub second).
• High Speed image reconstruction system.
• The high rating x-ray tube i.e. 8 MHU or more.
• Multiple reconstruction technique.
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19. Advancement in CT 19
FIGURE. (Left) SSCT arrays containing single, long elements along z-axis.
(Right) MSCT arrays with several rows of small detector elements.

20. In MDCT, advancement in following
feature
• Multidetector Rows
• CT tube
• Gantry rotation
• Data acquisition/Reconstruction
• Post processing Technique
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21. Multi detectors Rows
• Detectors measure the
intensity of radiation
transmitted through the
patient.
• In the advancement of
detectors, increase in
numbers, size and Z-axis
size of detector arrays.
• With multiple detector
array ,slice thickness
determined by detector
width.
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22. Detectors array configuration
• Matrix Type(uniform)
• Adaptive Type(non-uniform)
• Hybrid Type(mixed)
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23. Matrix detector array
• Equal width detectors.
• 16 rows of 1.25-mm
detectors (effective
width at isocenter are
aligned in the z-axis.
• To achieve different
slice widths, the
detectors are
electronically coupled
at the beginning of
each scan according to
the requested slice
width. Advancement in CT 23

24. Contd…..
Advancement in CT 24
•The total z-axis
dimension of the
detector covers 20
mm.
•This approach limits
the minimal z-axis
resolution to the
nominal width (at
isocenter) of the
individual detectors.

25. Adaptive detector array
• The variable-width detector.
• This approach is more
geometrically efficient
because there is less
unusable space in the z-axis.
• This combination also
permits slice widths as small
as 0.5 mm, enabling
isotropic imaging (i.e., sub
millimeter voxel dimensions
are equal in all planes.
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26. Contd…..
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27. Hybrid detector array
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28. Pitch
• The definition of pitch of MDCT is different
from the pitch of SDCT.
• In SDCT,
Pitch = table movement per rotation(I)/beam
width(W)
• In MDCT,
– Beam Pitch
– Detector pitch
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29. Contd…..
• Detector
pitch=I/T( table
increment per
rotation /slice
thickness)
• Beam Pitch =
Detector Pitch/N=
I/N x T = Pitch
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Diagram shows the concept of beam
pitch and detector pitch

30. Contd.…
Advancement in CT 30

31. Cone beam effect
• Multidetector CT complicates
fan-beam reconstruction
techniques by adding a
divergence of the fan beam
along the longitudinal axis (z-
axis), creating a cone shape.
• It can compensate by cone beam
reconstruction algorithm.
• For up to 4 slice MDCT, the cone
divergence is to be considered in
the interpolation process.
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Fig: The x-ray fan beam is divergent in the
z-axis, creating a cone beam

32. CT Tube
Today's CT tubes include
• Rotating anodes.
• Unique cooling methods.
• Variable moving focal spots on the anode.
• Up to 7 MHU of anode heat storage capability.
• Cooling rates as fast as 1 MHU/minute.
Advancement in CT 32

33. Straton tube (Siemens)
• New construction, focused
and deflected beam of
thermal electrons.
• The whole tube and anode
assembly rotates, bearing out
side with oil cooled.
• Zero heat storage
capacity(cooling is faster than
heat storage).
Advancement in CT 33

34. Contd…..
• Cooling rate-4.7 MHU/min cooled down
within -20 sec
• Enables gantry speed of 0.37 seconds per
rotation with tube current-500 mA.
• Anode diameter-120mm(tungsten zerconium
Mo).
• focal spot-tungsten and rhenium.
Advancement in CT 34

35. Rotalix ceramic Tube(Philips)
• In 1989 phillips became the first company to
introduce MRC.
• Based on the technology of spiral groove
bearing using liquid metal alloy as lubricant.
Advancement in CT 35

36. Contd…..
• Noiselessly rotating anode that could be
switched on in the morning and switched off
in the evening.
• Liquid metal alloy as lubricant, avoid waiting
time during and between examination.
• Higher output and longer tube life.
Advancement in CT 36

37. Contd…..
• 200 mm graphite backed anode
• Anode heat storage capacity -8 MHU
• Tube voltage 90 to 140 kv
• Tube current 20 to 500 mA
• Anode angle – 7o
Advancement in CT 37

38. Gantry rotation
Sub second gantry rotation
• In 16 slices - 0.5 sec.
• In 64 slices – 0.3 sec.
• In 256/320 slices – 0.27 sec.
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39. Reconstruction
Filtered back projection:
• this method is commonly used because it
allows short computation time with relatively
accurate solutions.
• Attempts to approximate the solution by
projection of a uniform value of attenuation
over the path of the ray such that the
calculated over path is proportional to the
measured attenuation.
Advancement in CT 39

40. Advancement in CT 40
Figure: Reconstruction by back-projection of a high-density object in diffuse medium.
Back-projection with 18 views (A), 36 views (B), and 72 views (C).
Notice improvement of the image but persistence of star patterns with an increasing
number of views

41. Contd……
• These values are then stored in the computer for
the matrix elements involved and the process is
repeated for each ray sum of the scan.
• Each matrix element thus receives a contribution
from each ray that passes through it.
• The final image obtained is rather blurred as a
result of the assumption that the beam
attenuation occurs uniformly over the entire path
of the ray.
Advancement in CT 41

42. Contd….
• No matter how many views are used,
however, the blurring effect is never
completely eliminated. Thus, mathematical
maneuver called a filtering, is used.
• The purpose of the filtering process is to
modify the ray sum data such that the back-
projections consist of both positive and
negative values.
Advancement in CT 42

43. Contd….
• With the continued development of larger,
more numerous detector elements,
reconstruction methods have more
remarkably complex.
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44. Interpolation
• is a reconstruction method that permits the
realignment of helical scan data for
reconstruction of an axial slice.
• To minimize motion artifacts, the volume of
collected data must be synthesized or
interpolated.
• The simplest form of interpolation is linear.
• Two common spiral linear interpolators are
shown in Figure.
Advancement in CT 44

45. Contd….
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Algorithms showing 360 degree and 180 degree linear spiral
interpolation. The 360 degree interpolator weights spiral data over two
revolutions of the gantry, and the 180 degree interpolator weights spiral
data over one revolution of the gantry.

46. Post processing Technique
• Multiplanar Reconstruction(MPR)
– MPR is the fast reconstruction method.
– Provide coronal or sagittal plane from axial
scan.
– Depend on acquisition parameter- thin
collimation excellent results.
– Commonly used in orthopedic examination
• Shaded surface display(SSD)
– Also called surface rendering
– The marching cubes algorithm must be
hallmark for surface rendering.
– Commonly used for fracture, deformities of
bone, CTA
Advancement in CT 46

47. Contd…
• Volume Rendering Technique(VRT)
– Representation, visualization &
manipulation of objects represented as
sampled data in 3 or more dimensions.
– Commonly used in CTA, CT Coronary
angiography
• Maximum Intensity Projection(MIP)/
Minimum Intensity Projection(MinIP)
– MIP is a relatively simple method.
– for visualization permits easy viewing of
vascular structures or air-filled cavities.
Advancement in CT 47

48. Contd…
• Virtual Endoscopy
– Used for 3D reconstruction of
upper GI.
• Virtual Colonoscopy
– Used for 3D reconstruction of
Colon.
• Virtual Bronchoscopy
– Used for 3D reconstruction of
airways.
Advancement in CT 48

49. Advantage of MDCT
• Improved temporal Resolution
– Because faster scanning time results in fewer
motion artifacts due to voluntary or involuntary
motion. Breath hold time reduced.
• Improved Spatial Resolution
– Because thinner slices improve resolution in the z-
axis, reducing partial volume artifacts and
increasing diagnostic accuracy.
Advancement in CT 49

50. Contd….
• Decreased image noise.
– Because more pt. length is scanned per rotation,
thus for extended length study the mA can be
increased, this decreases image noise and
improved image quality.
• Longer Anatomical coverage.
– Because of the more detector array, large body
area cover with in seconds.
Advancement in CT 50

51. Dual source MDCT
• Have developed dual x-ray
source CT scanners with
corresponding detectors in
the third-generation
configuration.
• The initial benefits-rapid
scan time and enhanced
characterization of tissue
properties.
• uses “air bearings” to
reduce friction and increase
the scan gantry rotation
speed.
Advancement in CT 51
Fig: configuration of dual x-ray sources
and detector systems

52. PETCT
• PET and CT provide
complementary
information.
• PET provides functional
information but little
anatomic detail.
• CT provides anatomic and
morphologic information
(size, shape, density of
lesions ) but provides little
physiologic insight into
tissues
Advancement in CT 52

53. Conclusions
• The advancement of CT technology is due to
the development in slip ring technology and
multidetector configurations.
• Due to the advancement in MDCT, the
radiological diagnosis is more accurate.
• This advancement is going on forward with
upcoming time.
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54. References
• CT and MRI of whole body- J.R.Hagga, fifth edition.
• Radiology book for Technologists-S.C.Bushong, ninth
edition.
• Essential book of Physics-Busburg, second edition.
• Principle of Multislice CT, Lee W. Goldman ,journal of
Nuclear Medicine Technology.
• Multidetector CT, from journal of RSNA.
• Recent advances in CT - Mahadevappa Mahesh,
Ph.D.
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55. Advancement in CT 55

56. Questions
• Define Helical CT Scan?
• What is Slip ring Technology?
• What are the different between SDCT and
MDCT?
• Describe the different type of detector
configuration?
• What is pitch? What is role of pitch on pt dose?
• What are the Post processing Technique?
• What are the advantages of MDCT?
4/24/2022 Advancement in CT 56