Computerized tomography (CT) uses X-rays and digital image processing to generate cross-sectional images of the body. Godfrey Hounsfield invented the first commercially viable CT scanner in 1972. CT scans provide more detailed images than traditional X-rays by using multiple angles to reconstruct cross-sectional slices of the body. Modern CT scanners can obtain these slices quickly, in under one second, allowing imaging of moving structures like the heart.

1. COMPUTED TOMOGRAPHY
CT SCAN
BY SAJID EJAZ

2. INTRODUCTION
• Computer tomography (CT), originally
known as computed axial computed axial
tomography (CAT or CT scan) and body
section rentenography.
• It is a medical imaging method employing
tomography where digital geometry
processing is used to generate a three-
dimensional image of the internals of an object
from a large series of two-dimensional X-ray
images taken around a single axis of rotation.

3.  The word "tomography" is derived from the
Greek tomos (slice) and graphein (to write).
CT produces a volume of data which can be
manipulated, through a process known as
windowing, in order to demonstrate various
structures based on their ability to block the
Xray beam.

4. HISTORY
 The first commercially viable CT scanner
was invented by Godfrey Newbold
Hounsfield in Hayes, England at Thorn EMI
Central Research Laboratories using X-rays.
 Hounsfield conceived his idea in 1967, and
it was publicly announced in 1972.
 It is claimed that the CT scanner was "the
greatest legacy" of the Beatles; the massive
profits from their record sales enabled EMI
to fund scientific research.

5. ADVANTAGE OF COMPUTED
TOMOGRAPHY OVER
CONVENTIONAL RADIOGRAPHY
 To overcome superimposition of structures.
 To improve contrast of the image.
 To measure small differences in tissue
contrast.

6. PRINCIPLE OF TOMOGRAPHY
 The internal structure of the object can be
reconstructed from multiple projections of the
object.
 Mathematically principle of CT was first
developed in 1917 by Radon.
 Proved that image of unknown object could be
produced if one had several number of
projections throughout the object.

7. VARIOUS PARAMETER OF CT
 SLICE
 MATRIX
 PIXEL
 VOXEL
 CT NUMBER
 WINDOWING
 WINDOW WIDTH
 WINDOW LEVEL
 PITCH

8. SLICE/CUT
 The cross section
portion of body which
is scanned for
production of CT
image is called Slice.
 The slice has width
and therefore volume.
 The width is
determined by width
of the x rays beam.

9. MATRIX
 The CT image is represented as the Matrix
of the number.
 A two dimensional array of numbers
arranged in rows and columns is called
Matrix.
 Each number represent the value of the
image at that location.

10. PIXEL
 Each square in a matrix is called a pixel.
 Also known as picture element.
VOXEL
 Each individual element or number in
the image matrix represents a three
dimensional volume element in object
called VOXEL.

11. CT NUMBER
 The numbers in the image matrix is called
CT NUMBER.
 Each pixel has a number which represents
the x-ray attenuation in the corresponding
voxel of the object.

12. HOUNSFIELD UNIT (HU)
 Related to different composition and nature
of Tissue.
 The CT NUMBER is also known as
Hounsfield units(HU).
 Represent the density of tissue.
 Different Tissue have different CT number
Range in HU.

13. WINDOWING
 It is a system where the CT no. range of
interest is spread cover the full grey scale
available on the display system.
 WINDOW WIDTH –Means total range of CT
no. values selected for gray scale
interpretation. It corresponds to contrast of the
image.
 WINDOW LEVEL– represents the CT no.
selected for the centre of the range of the no.
displayed on the image. It corresponds to
brightness of image .

14. PITCH
 The relationship between patient and tube
motion is called Pitch.
 It is defined as table movement during each
revolution of x-ray tube divided by collimation
width.
 For example: For a 5mm section, if patient
moves 10mm during the time it takes for the x-
ray tube to rotate through 360˚, the pitch is 2.
 Increasing pitch reduces the scan time and
patient dose.

15. GENERATION OF CT
 First Generation:-
 Narrow pencil beam
 Single detector
 Detector used is made up of NaI.
 Translate –Rotate movements of Tube-
detector combination
 Scan time-5mins.
 Designed only for evaluation of brain.

16. FIRST GENERATION CT SCAN
 Head kept enclosed in
a water bath
 Paired detectors
 A reference detector

17. SECOND GENERATION OF CT
SCAN
 Narrow fan beam
 Linear detector array(5 to30)
 Translate-Rotate movements of
Tube-Detector combination
 Fewer linear movements are
needed as there are more detectors
to gather the data.
 Between linear movements, the
gantry rotated 30o
 Scan time~30secs(advantage over
first generation)

18. THIRD GENERATION OF CT
SCAN
 Rotate(tube)Rotate(detectors) Motion.
 Pulsed wide fan beam.
 Arc of detectors(600-900)
 Detectors are perfectly aligned with the X-Ray
tube
 Both Xenon and scintillation crystal detectors can
be used
 Scan time< 5secs
 Disadvantage: Ring Artifacts due to electronic

19. THIRD GENERATION OF CT
SCAN

20. FOURTH GENERATION OF CT
SCAN
 Complete circular array of about 1200 to 4800
stationary detectors
 Single x-ray tube rotates with in the circular array
of detectors
 Wide fan beam to cover the entire patient
 Scan time of newer scanners is about ½ s or, <2s.
 Designed to address ring artifacts by keeping
detector assembly stationary.
 Disadvantage: High cost.

21. FOURTH GENERATION OF CT
SCAN

22. FIFTH GENERATION OF CT
SCAN
 Stationary/stationary
 Developed specifically for cardiac tomographic
imaging
 No conventional x-ray tube; large arc of tungsten
encircles patient and lies directly opposite to the
detector ring
 Electron beam steered around the patient to strike
the annular tungsten target
 Capable of 50-msec scan times; can produce fast-
frame- rate CT movies of the beating heart.

23. FIFTH GENERATION OF CT
SCAN

24. CT BASICHARDWARE
A-X-ray tube
B-Collimators
C-Detectors – Scintillation crystals
-Xenon gas ionisation chambers
-Ceramic scintillators

25. X-RAY TUBE
• Focal spot:0.6mm
• Annode heat capacity

26. TWO COLLIMATORS IN CT
PREPATIENT COLIIMATORS
• Determine slice
thickness
• Reduce patient dose
PREDECTOR COLLIMATORS
• Reduce scattered
radiation to improve
contrast
• Helps determine slice
thickness

27. Thank you…