This document summarizes the evolution of computed tomography (CT) technology over several generations: - 1st generation CT scanners from the 1970s took 5 minutes to generate a single image using a pencil-shaped beam and single detector. - 3rd generation scanners from the 1980s reduced scan time to 3-5 seconds using a fan beam and detector array while rotating continuously. - Current multislice CT scanners can scan multiple slices simultaneously in under 1 second using multiple detector arrays. - The latest technology uses a stationary beam and detector configuration to achieve scan times under 50 milliseconds.

1. ‫تعلم‬ ‫تكن‬ ‫مالم‬ ‫وعلمك‬
‫هللا‬ ‫فضل‬ ‫وكان‬
‫عظيما‬ ‫عليك‬

2. Basics Of Computed
Tomography (CT)
Lecture Three
Gamal Fathalla M.
Mahdaly
gamal_mahdaly@hotmail.com

3. Computed Tomography
 1- A highly collimated X-Ray beam is transmitted through a specific
cross-section of the patient.
(No superimposition- Minimal scattered radiation resulting in better
Contrast Resolution).
 2- This beam is variably attenuated in the body of the patient by
different anatomies with different densities
 3- The attenuated beam strikes special detectors , these detectors
are quantitative and measure subtle attenuation differences
resulting in high Spatial Resolution.
 4- The data from the detectors are processed by digital computer
(ADC) that uses special algorithms to reconstruct an image of cross-
section in different ways & different filters.
 5- The computed motion of the cradle together with the collimation
helps determine the slice thickness.

4. c.f. www.sprawls.org, computed tomography lecture
Formation of a CT image - Tomographic Acquisition
Before the axial acquisition of the next slice, the table that the patient is
lying on is moved slightly in the cranial-caudal direction or the z-axis of
the scanner
This positions a different slice of tissue in the path of the x-ray beam
for the acquisition of the next image
High kV of 120 to 140, mA ranging from 10 – 440 and scan times of
0.4 – 2 seconds

5. Voxel and pixel
Voxel =
(Volume element)
Pixel =
(Picture element)

7. Each cell in a CT scan matrix is a two dimensional
representation (pixel) of a volume of tissue (voxel).

8. Field of view (FOV):
The diameter of reconstructed image
Matrix :
 Orderly array of cells fashioned in rows
and columns.
 Current CT Scanners produce 512x512
images and 1024x1024 is available on
many.

9. Just 4 history: The 1st
generation head scanner

10. 1st Generation 5- min scan time
Moving in translate-rotate configuration.
Pencil- shaped beam.
Single detector.

11. In 1972, the EMI scanner was the First CT scanner introduced into Clinical practice.
5 minutes/ONE image
1st generation
Rotate/Translate, Pencil Beam, Single Detector

12. 2nd generation 5minutes/ONE Image
Translate/Rotate, Fan beam, Detector array.
Disadvantages of fan beam:
1-increase scatter radiation
2-incraese radiation intensity toward the edges due to body shape

14. 3rd generation 3-5 sec scan time.
Rotate/Rotate, Fan beam, Detector array.
Disadvantage: Ring artifacts
3-5 sec.scan time.

15. 3rd generation: Formation of CT image
You could have approx. 800 rays taken at 1,000 different projection angles
giving 800,000 transmission measurements

16. The linear detector array is characteristic of first- and second
generation ; the curvilinear array is in 3rd and 4thgeneration
The collimation is positioned on
either side of the slice to be scanned.
Constant source-to-detector
path length which was
advantage for good image
reconstruction.
Better x-ray beam
collimation to reduce the
effect of scatter radiation.

17. 4th generation 1sec scan time
Rotate/Stationary configuration, Fan beam ,Detector array
Rotating tube facing stationary detectors

18. 5th Generation 50 m.Sec Scan Time
Stationary/Stationary, Electron Beam scanner
Primarily for cardiologists,
Uses tungsten target and high-energy electron beam

19. 5th generation Electron Beam CT Scanner
A waveguide accelerates a focused electron beam onto a semicircular
tungsten target through a bending magnet. Actually, there are four tungsten
targets, so four tissue slices are scanned at the same time. Nothing moves
except the electron beam. Scan time 50 ms.

20. Patient is transported continuously through
gantry while data are acquired continuously
during several 360-deg rotations
6th generation (Helical/Spiral CT)

21. 6th generation (Helical/Spiral CT)
The movement of the x-ray tube is not spiral. It appears that way
because the patient moves through the plane of rotation during the
image.

22. Contiguous separate (axial)
acquisition (a)
Corresponds to complete
slice contour (b)
Helical acquisition (c) due to
table motion while X-Ray is on
corresponds
To incomplete slice contour (d)

23. 7th generation (MULTISLICES helical scanner)
SINGLE V/S MULTISECTION SCANNER
•EFFICIENT X-RAY TUBE USE.
•LONGER ANATOMIC COVERAGE/S

24. Advantages Spiral CT vs
Conventional CT
 Faster image acquisition.
 Quicker contrast follow up.
 Reduced patient dose at Pitch>1.
 Physiologic monitoring.
 Improved 3D imaging.
 Angiographic imaging.
 Fewer partial volume artifacts
 Fewer motion artifacts
 Freeze breathing.
 No Mis-registration.
 Increased output.
 Improved patient comfort
 Real time CT guided biopsy.

25. Any Question???.
Take your Tiiime!!! .
Again Any Question???.
Otherwise, I’m going to ask!!!.
Should I Ask???.

26. Have a nice day