Sir Godfrey N. Hounsfield invented the CT scan in 1972, presenting the first cross-sectional image of the internal structures of the brain without surgery. CT works by reconstructing internal structures from multiple X-ray projections taken around an object at different angles. Compared to conventional radiography, CT provides more accurate diagnostic information by not collapsing 3D structures onto a 2D image. CT continues to advance with improvements such as faster scanning times, higher resolution images, and the ability to produce 3D volume images.

1. SHIVAPRASAD
CT/MRI TECHNOLOGIST
Computed Tomography

2. History Of CT Scan
Sir Godfrey N. Hounsfield invented the CT scan in
the year 1972 and called computerized axial
transverse scanning.
He presented a cross-sectional image of the head
that revealed the internal structures of the brain in a
manner previously only seen at surgery or autopsy
and for the first time pathologic processes such as
blood clots, tumors, and strokes could be easily seen
noninvasively.

3. BASIC PRINCIPLE:
The Internal Structures of An Object Can Be
Reconstructed From Multiple Projections Of The
Object.
By assigning different levels to different attenuation
coefficients, an image can be reconstructed with aid
of computer that represent various structures with
diff attenuation properties.

4. COMPARISION OF CT WITH
CONVIENTIONAL RADIOGRAPHY
Conventional radiography suffers
from the collapsing of 3D structures
onto a 2D image.
CT gives accurate diagnostic
Information about the distribution
of structures inside the body.

5. VARIOUS PARAMETERS OF CT
SLICE
MATRIX
PIXEL
VOXEL
CT NUMBER
WINDOWING
WINDOW WIDTH
WINDOW LEVEL
PITCH

6. 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.

7. 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.

8. Pixel
Each square in a matrix is called a pixel.
 Also known as picture element.

9. VOXEL

10. CT Number
The CT Scanner calculate from the collected data
from the linear coefficient in each pixel.
After computer calculates a value for the linear
attenuation coefficient in a pixel. the value is
converted into new number called CT number

11. Windowing
Windowing is a system where the CT no. range of
interest is spread cover the full grey scale available
on the display system

12. 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 center of the range of the no. displayed on the
image. It corresponds to Brightness of image.

13. 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.

14. First Generation

15. Second Generation

16. Third Generation

17. Fourth Generation

18. Fifth Generation(EBCT)
 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

19. Sixth Generation( Spiral CT)

20. Seventh generation
Single x ray tube
Cone beam
Multiple of detectors array
Fast 3D images
Disadvantages – Expensive

21. COMMON CT ARTIFACTS:
Artifacts Cause Correction
Motion Artifact Patient movement
(Resp/heart)
 Reduction in scan time
 Clear and concise instruction to the patient
 Proper patient immobilization
 If needed, administration of
sedatives/antiperistaltic drugs
Streak Artifact - Due to Metals or implants Using Gantry Angulation
Metal/Streak reduction protocols
Beam Hardening Due to Polyenergetic
Spectrum
Beam Hardening Correction Algorithm
Partial Volume Averaging Presence of tissues with
highly varying absorbtion
properties in a voxel.
Usage of Thinner CT slices
Ring Artifact Due to Detector failure or
miscalibration
Regular quality assurance checks