The document provides an overview of the evolution of computed tomography (CT) scanners, detailing their capabilities and design changes from first generation to fifth generation. Key developments include advancements in scanning speed, image quality, and detector configurations, culminating in modern technologies such as spiral/helical CT and multi-slice CT that enhance diagnostic imaging. It also discusses the implications of various scan types on radiation exposure and their specific applications in medical imaging.

1. CT- GENERATIONS
Adavala.Mallikarjuna
45th DRP
Guide: Shri K.K.Sanu

2. Introduction of CT scan solves the major drawbacks
of conventional radiography Viz. superposition of
overlaying structures and scatter.
Both these reduces image contrast.
In the early1970s Godfrey Hounsfield developed a
scanner and demonstrated.
Cormack is a physicist who developed mathematics
for the reconstruction of image from multiple
projections.
The basic principle of computed tomography is
reconstruction of image from multiple projections.
In1979 Hounsfield and Cormack shared Noble prize
in medicine for this invention.

3. CT scanners are classified into different
categories
Based on source detector configuration and
their relative movement.

4. Original EMI Scanner

5. The original EMI scanner consists of an X-ray tube
and a pair of detectors.
Tube and detectors are mounted on a gantry
opposite to each other.
A reference detector is placed in the path of X-ray
beam before it reaches to the patient.
The source-detector system makes linear and
rotatory motions.
The linear motion was repeated over and over for
180 times.
Between each of these linear movements the gantry
rotated 10 .

6. The axis of rotation passes through the centre of the
patient head.
The X-ray tube was on during linear motion and off in
rotatory motion.
The transmitted X-rays was measured for 160 times
during the linear motion.
Total 28,800 projections are counted.
The total scan time was 5 min and reconstruction time
is 1 min.
For 10 slices the scan time is about 25 to 30 min.

7. First Generation CT Scanner
The original EMI scanner belongs to first generation
CT scanner.
In all other first generation CT scanners only one
detector per slice.
Detector used in this CT scanners was NaI(Tl).
Image quality is excellent in this type of CT
scanners.

8. Second Generation CT Scanner

9. Second Generation CT has Rotate-Translate
movement.
In this narrow fan beam and an array of detectors are
used. About 30 detectors are arranged along an arc.
Due to the increased utilization of X-ray output (about
30 times more than the first generation) scan time was
reduced.
Scan time per slice reduces to 10 to 90 sec.
Inclusion of scatter component is more in this
generation compared to first generation.

10. Third Generation CT Scanner

11. In third generation CT scanners, translational motion
is completely removed.
X-ray tube and detector system makes rotatory
motion around the patient for acquiring information,
hence it is called Rotate-Rotate movement.
In this, a wide fan beam is used to cover the entire
body and more no of detectors (more than 800) are
used.
In this system, scan time reduces to about 5 seconds.
Newer systems have scan time of about 1.5 sec.
A single detector towards the end of array acts as the
reference detector.

12. In third generation CT the major drawback is ring
artefact.
This is due to the failure of detector.
This problem is rectified in fourth generation CT
scanners by the use of stationary detector ring.

13. Fourth Generation CT Scanner

14. Rotate – Stationary movement.
In this system a detector ring is used around
the patient. X-ray tube is rotating inside the
detector ring.
Each detector acts as its own reference
detector.
Scan time is reduced to about 1 sec.

15. Fifth Generation CT Scanner/
Electron beam CT

16. No moving parts.
In this a large arc of tungsten is used as X-ray target .
Detector ring is positioned directly opposite to the
tungsten arc.
An electron beam steered through a wave guide to
strike the tungsten arc through a bending magnet to
produce x-rays.
It is not very common type.

17. During the X-ray production patient couch is
moved to image different body cross-sections.
Capable of 50 m sec scan time.
It can produce fast-frame-rate CT moves of
beating heart.
It has special applications in cardiology

18. Slip ring technology
In previous generations, the rotation of source -
detector system around the patient was carried out
by the movement of the system through 3600 rotation
in one direction for a scan and in opposite direction
for the next scan.
Continuous rotation of source-detector system
became possible with the introduction of Slip-ring
technology.
Slip-ring technology is used in modern CT scanners

19. Spiral / Helical CT

20. In spiral CT source and detector system makes
continuous motion around the patient, the couch too
moves continuously into the axial direction.
As a result x-ray beam follows a spiral/helical trajectory
hence the name is spiral/helical CT.
Speed of rotation of the gantry and speed of table
determines the pitch of the helix.
Pitch =couch movement per 3600 / Slice thickness.
During the spiral CT scan image data is received
continuously

21. However the data obtained during spiral scan may not be
sufficient for reconstruction of images of all slices along
the axial direction.
Therefore image reconstruction in spiral CT is done by
the interpolation of data available at 3600 apart.
Entire scan can be done in a breath hold time.
Axial resolution decreases with increase in pitch.Smaller
pitch increase patient dose.
Longer processing time as more data have to be
handled.

22. Spiral CT is advantageous in CT Fluoroscopy as use of
contrast media can be minimised .
Reconstruction of images is possible in different planes
3D image too can be reconstructed.
Applications of Spiral/helical CT

23. MULTI SLICE CT
 The principle in multi slice CT is similar to the
helical / spiral CT but there are more number of
detector channels.
 No. of channels : 4, 8, 16, 32, 40 & 64.
 use of cone beam
 The major advantage of multi slice CT is more
volume is covered in a single scan .
 Effective utilization of x-ray beam.

25. Generation Configuration Detectors Beam Min Scan Time
First Translate-rotate 1~2 Pencil thin 2.5 min
Second Translate-rotate 3~52 Narrow fan 10 sec
Third Rotate-rotate 256~1000 Wide fan 0.5 sec
Fourth Rotate-fixed 600~4800 Wide fan 1 sec
Fifth Electron beam 1284 detectors
Wide fan
beam
33 ms

26. Examination Typical effective dose (m Sv)
Chest X-ray 0.1
Head CT 1.5
Abdomen CT 5.3
Chest CT 5.8
Chest, Abdomen and Pelvis
CT
9.9
Cardiac CT angiogram 6.7-13
CT colonography (virtual
colonoscopy)
3.6 - 8.8

27. Thank you