This document summarizes the history and generations of computed tomography (CT) scans. It discusses 7 generations of CT scanners: 1) first generation used a translate-rotate motion with one detector, 2) second generation used translate-rotate with multiple detectors, 3) third generation used continuous rotate-rotate motion, 4) fourth generation used a rotate-fixed system with many detectors, 5) fifth generation could acquire data 10x faster, 6) sixth generation introduced spiral/helical scanning, and 7) seventh generation may use flat panel detectors. Each generation enabled faster scanning and improved imaging capabilities.

1. BASIC AND
GENERATIONS OF
COMPUTED
TOMOGRAPHY
MR. ROHIT BANSAL
ASISTANT PROFESSOR
MAMC (AGROHA)

2. CT scan is an computer assisted tomography
which scans an object in a cross sectional
format in defined thickness that is free from
superimposing of an overlaying structures by
which computerized mathematical
reconstruction process.

3.  1st approach done by mathematician J.Radon uses infinite sets of
projection to reconstruct the 2D &3D images of internal structure with
complex mathematics in 1917.
 Work continued by Bracewell (Radio astronomer) made soler map from
multiple ray projection in 1956.
 Oldendorf (1961) & Allen comark in 1963 made his computed assisted
tomographic laboratory model.
 Khul &Edward in 1968 made a type of scanner used in nuclear
medicine.
 But the technique of imaging was embedded in medical imaging by Sir
Godfrey N. Housnfield in 1972,worked at EMI laboratories.
History of CT Scan

4.  Basic principle of CT is that internal structures of an object can be
reconstructed from the multiple projection of an object.
 In early CT imaging devices (scanners) a narrow x-ray beam is scanned
across a patient in a synchrony with a radiation detector on the opposite
side of the patient.
 If the beam is monoenergetic or nearly so the transmission of x-ray
through the patient is
I=Io e-ux
 Where:
 I= intensity of photon transmitted across some distance x.
 Iø= initial intensity of photon.
 e= proportionality constant.
 u= the linear attenuation coefficient.
 X= distance travelled.
BASIC PRINCIPLE OF CT SCAN

5. SCANING MOTION:-
 CT scanners have gone through a number
of design changes since the technology was
first introduced in 1971.
 Scan time reduction is the predominant
reason for introducing new configurations.
 We will discuss geometry of design in five
categories:
1. First generation (translate-rotate, one
detector) .
2. Second generation (translate-rotate,
multiple detectors) .
3. Rotate-rotate (third generation) .
4. Rotate-fixed (fourth generation) .
5. Other geometries.

6. The first EMI brain scanner and other earlier scanners were based on
this concept.
Parallel pencil beam geometry is used.
The data acquisition process is based on a translate-rotate principle.
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.
First-generation CT scanners took at least 4.5 to 5.5 minutes to produce
a complete scan of the patient.
Matrix 80x80.
Tube operated at 130 kVp and 33 mAs.
Only head scan is possible in first generation.
NaI detectors are used.
First-Generation Scanners (1971-72)

8. 1st Generations CT Scan Image

9. The data acquisition process is based on a translate-rotate principle.
30 detectors are used.
Narrow fan shaped beam is used (5-10 degree divergence).
 Bow - tie filters are used.
 Detector are made up of NaI .
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.
The larger rotational increments and increased number of detectors
result in shorter scan times that range from 20 seconds to 3.5 minutes.
Rotary movement was in arc of 10º & linear movements were 18 as
compare to EMI scanner.
Increased scatter radiation due to fan beam.
Second-Generation Scanners (1974)

12. Third-generation CT scanners were based on a wide fan beam
(35-45 degree) geometry that rotates continuously around the
patient for 360 degrees.
 Array of 600- 900 detectors.
 Xenon gas detectors are used.
 Rotate rotate configuration.
 Scan time is 1 sec.
 Ring artifact is shown in this generation.
Third-Generation Scanners (1977)

15. Based on Rotate-fixed system i.e. tube rotates through 360º &
detectors stationary
A ring of detectors (1000-4500) surrounds the patient.
Wide Fan shaped beam (48-120 degree).
Scan time very short i.e. Less than 1 sec (vary from scanner to
scanner, depending on the manufacturer).
High cost because more no of detector use
More scatter radiation.
Solid state detectors are used.
Higher patient dose.
Ring artifact is removed.
Fourth-Generation Scanners (1980)

18. 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 (McCollough, 1995). 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.”).
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
Fifth-Generation Scanners

19. The basic configuration of an EBCT scanner is :
At one end of the scanner is an electron gun (320cm long ) 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 (180cm in diameter). These stationary
rings span an arc of 210 degrees. 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 (McCollough, 1995). 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.
Scan time- below 50 ms.

21. Introduced in 1989 by Dr. Kalender
Spiral CT is made possible by the use of slip ring technology. Slips rings
are an electromechanical devices that conduct electricity and electrical
signals through ring & brushes from a rotating surface onto fixed surface &
vice-versa.
Composite brushes are made up of conductive material (silver graphite)
Brushes are to be replaced every yr. or during preventive maintenance.
 3 kind of slip rings are used
-1st provide high & low voltage to X ray tube
-2nd provide low voltage to control system on gantry
-3rd transfer signal from rotating detectors array to DAS
Helical /Spiral CT refers to continuous gantry rotation with simultaneous
couch increments. In this mode a sequence of adjacent scans that may
overlap are continuously obtained.
A reconstruction algorithm interpolates the angular data from adjacent
scan into a single parallel cross section slice.
Helical units are capable to scan in both axial as well as helical mode
Sixth Generation (MSCT/DECT)

24. Seventh generation CT Scanners are 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.
Perhaps they may be labeled seventh-generation CT scanners on the basis of
the simple categorization mentioned above.
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.
The combination of area detectors that provide sufficient image quality
with fast gantry rotation speed will be a promising technical concept for
medical CT systems.
Seventh Generation CT scanner