CT Scanner Physics for Medical Physicists and Nuclear Medicine and Radiology. Shahid Younas, Sr. Medical Physicist &RPA, SKMCH&RC, Lahore, Pakistan

1. Introduction to CT Physics
Shahid Younas

2. Introduction to CT Physics
Computed Tomography

3. X rays
Electromagnetic
0.01- 10 nm
30 PHz to 30
Hexa Hz

4. PET CT / Cyclotron- the Cycle

5. PET CT / Cyclotron- the Cycle
Highly energetic electrons interact
with matter and convert their
kinetic energy into
electromagnetic radiation.

6. X ray Production Device
Electron source
(Filament)
Glass tube
(Evacuated)
Target (Cathode)

7. Bremsstrahlung X Rays

8. Bremsstrahlung X Rays
The electron accelerates then
suddenly de-accelerates, causing
electromagnetic radiation equal to
that of the change in kinetic
energy of the electron.

9. Bremsstrahlung X Rays
The energy of the E= mc2 has
a continuous spectrum up to a
maximum, equal to the
maximum kinetic energy of the
electron.

10. Bremsstrahlung X Rays
The production of
Bremsstrahlung radiation
increases with the atomic
number of the target atom;
thus, it increases electrostatic
attraction.

11. Bremsstrahlung X rays

12. Bremsstrahlung X rays

13. Bremsstrahlung X Rays
Do you know peak voltage (Vp).

14. Characteristic X Rays

15. Brem + Char; = Continuous

16. Characteristic X Rays

17. Characteristic X Rays

18. Introduction to CT Scanner History
Roentgen was
beginning …..

19. Introduction to CT Scanner History
He was actually working
on properties of “cathode
rays”.

20. Introduction to CT Scanner History
Roentgen, like many husbands,
wanted to get rid of …… so ………

21. Introduction to CT Scanner History
‘‘X-ray mania’’

22. Introduction to CT Scanner History
… and then since 1896 she ….

23. Introduction to CT Scanner History
 This is an era of “planer radiology”.
 The discovery of X-rays was a necessary but insufficient
condition for the rise of computed tomography.
 Its design also depended on the development of
computational techniques.

24. Introduction to CT Scanner History
Allan MacLead Cormack (a), Godfrey Newbold Hounsfield (b)

25. Introduction to CT Scanner History

26. The EMI Mark I scanner (a) and a transverse image of the brain (b)

27. The EMI scanner with instrumentation and images obtained with it (a),
and the front cover of a company brochure describing the new
technology

28. EMI CT Scanner
 The basic parameters of the scanner used at that time were
as follows:
 scan time: about 4.5 min,
 reconstruction time: 20 s,
 cross-section thickness: 13 mm,
 image matrix: 80 x 80 pixels, where each pixel
represented an area 3 9 3 mm.

29. X Ray Tube
Do you know which algorithm was used by Hounsfield in the
first CT Scanner?
Algebraic Reconstruction Technique (ART)

30. X Ray Tube
 The x-ray tube provides an environment for x-ray
production via bremsstrahlung and characteristic radiation
mechanisms.
 Major components are the cathode, anode, rotor/stator,
glass (or metal) envelope, and tube housing.

31. X Ray Tube
The major components
of a modern x-ray tube
and housing assembly.

32. X Ray Tube
 For diagnostic imaging, effective peak voltage ranging
from 20 to 150 kVp.
 The tube current is the rate of electron flow from the
cathode to the anode.
1 mA = 6.24 X 1015 electrons/see.

33. X Ray Tube
Do you know the difference between KVp and KeV?
Peak Voltage (Vp) is the pushing force whereas
Electron Volts is a unit of energy

34. X Ray Tube
 For continuous fluoroscopy the tube current is typically 1
to 5 mA, and for projection radiography tube currents
from 100 to 1,000 mA are used with short exposure times
(less than 100 msec).

35. X Ray Tube
The kVp, mA, and exposure time are the three major
selectable parameters on the x-ray generator control panel
that determine the x-ray beam characteristics (quality and
quantity). These

36. Introduction to CT Scan
FDG PET-CT Imaging – What Every Imaging Specialist Should Know
Thanks