1. Computed Tomography / Spiral Computed Tomography 2. Clinical and Principle Operation of Computed Tomography 3. Law and Regulation in Malaysia 4. Radiation Dose

1. RADIOLOGIC IMAGING
LECTURER: MDM NADHIRAH
BY:
FATIN NAJIHA
JAMES JACKY

2. Patient undergoing CT of the abdomen. Drawing shows
the patient on a table that slides through the CT
machine, which takes x-ray pictures of the inside of the
body.

3. INTRODUCTION
 Computed Tomography is a well accepted imaging
modality for evaluation of the entire body.
 Computed Tomography(CT) Scan Machines Uses X-
rays, a powerful form of Electromagnetic Radiation.
 The images are obtained directly in the axial plane of
varying tissue thickness with the help of a computer.
 Some pathology can be seen in saggital or coronal
plane by reconstruction of the images by computer.
 CT has undergone several evolutions and nowadays
multi- detectors CT scanners have been evolved which
have better application in clinical field.

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. COMPARISION OF CT WITH CONVIENTIONAL
RADIOGRAPHY.
A conventional X-ray image is basically a shadow.
Shadows give you an incomplete picture of an object's shape.
This is the basic idea of computer aided tomography. In a CT
scan machine, the X-ray beam moves all around the patient,
scanning from hundreds of different angles

6. Comparison of CT with
Conventional Radiography
Radiographic procedure is qualitative and not quantitative

7. ADVANTAGE OF COMPUTED
TOMOGRAPHY OVER CONVIENTIONA
RADIOGRAPHY.
To overcome superimposition of structures.
 To improve contrast of the image.
 To measure small differences in tissue
contrast.

8. TOMOGRAPHY
 Imaging of Layer/Slice.
Principle
Images of structures lying above and below the plane
are blurred out due to motion unsharpness while the
structures lying in plane of interest appear sharp in in
the image.

9. Tomography

10. PRINCIPLE OF COMPUTED
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.

11. VARIOUS PARAMETERS OF CT
• SLICE
• MATRIX
• PIXEL
• VOXE L
• CT NUMBER
• WINDOWING
• WINDOW WIDTH
• WINDOW LEVEL
• PITCH

12. 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.

13. Cross Sectional Slices
Think like looking into the loaf of bread by cutting into
the thin slices and then viewing the slice individually.

14. 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.

15. PIXEL
 Each square in a matrix is called a pixel.
 Also known as picture element.

16. VOXEL
 Each individual element or number in the image
matrix represents a three dimensional volume element
in object called VOXEL.

17. 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.

18. HOUNSFIELD UNITS(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.

19. TISSUE AND CT NUMBER
APPROXIMATE

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

21. 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.

22. STEPS OF CT IMAGE
FORMATION

23. Phase of CT scanning
1.Scanning the patient or data Acquisition
a)X-ray Generator
b)X-ray Tube
c)X-ray Filtration System
d)Detector System
2.Reconstruction
a)Simple back projection
b)Iterative method
c)Analytical method
3.Display

25. During CT Scan (Procedure)
1) Patient lie on a narrow, motorized table that slides through
the opening into a tunnel.
2) Straps and pillows may be used to help the patient to stay in
position. During a head scan, the table may be fitted with a
special cradle that holds patient's head still.
3) While the table moves patient into the scanner, detectors and
the X-ray tube rotate around the patient. Each rotation yields
several images of thin slices of the body.
4) A technologist in a separate room can see and hear the
patient. Patient able to communicate with the technologist
via intercom.
5) patient need to hold their breath at certain points to avoid
blurring the images.

26. How a CT system
works:
1. A motorized table moves the patient
through a circular opening in the
CT imaging system.
2. While the patient is inside the
opening, an X-ray source and a
detector assembly within the system
rotate around the patient. A single
rotation typically takes a second or
less. During rotation the X-ray
source produces a narrow, fan-
shaped beam of X-rays that passes
through a section of the patient's
body.

27. 3. Detectors in rows opposite the X-ray
source register the X-rays that pass
through the patient's body as a snapshot in
the process of creating an image. Many
different "snapshots" (at many angles
through the patient) are collected during
one complete rotation.
4. For each rotation of the X-ray source and
detector assembly, the image data are sent
to a computer to reconstruct all of the
individual "snapshots" into one or multiple
cross-sectional images (slices) of the
internal organs and tissues.

28. Fractures as seen on
a CT scan.
Source: James
Heilman, M.D.,
[CC-BY-SA-3.0]

29. Axial view shows the circular dissection
membrane in the aortic arch.
Dissection of the complete thoracic aorta

30. Sagittal view
demonstrated the
dissection via the
descending aorta
down to the arteria
mesentrica inferior.
Dissection of the complete thoracic aorta

31. The entry was just at
the level of the aortic
root and extended via
the large ascending
aorta and the aortic
arch to all three
supra-aortic vessels
(brachiocephalic
trunk, carotid artery
and subclavian
artery).
Dissection of the complete thoracic aorta

33. HELICAL CT
 A technique where by the patient is transported
continuously through the gantry while data are
acquired continuously during several 360 degrees
scans.
Also k/a spiral or volume CT.

34. Advantages of helical CT
• Increased speed a study.
• Exact continuity of images.
• Less slice misregistration.
• Less motion artifact.
• Need for less contrast medium.
• Availability of volumetric data.

35. 1. Slip ring device
2. More efficient tube cooling
3. Increased milliampere capability
4. Smoother table movement
5. Software adjustment for table
movement
6. Efficient detectors

36.  Is one of the important parts of spiral CT
machines.
 Serves as a connection of the gantry rotating
part and the fixed portion of the power line
and the signal line.

37. Slip-ring technology

38. Adjustment in reconstruction
algorithm
Interpolation algorithm
 Estimation of a unknown value between known
values is called interpolation.
 Estimation of a unknown value beyond known
values is called extrapolation.

39.  Pitch: relation of table speed to slice
thickness  Pitch= Table feed
* time per
rotation of 360
collimation
 Pitch= Table feed , if it
is a 1 sec scan.
collimation

40. Limitations
• Requires very cooperative patient.
• Costly machine and X-ray tube.
• Loss of image resolution because of the interpolation
required to process data.

42. RADIATION DOSE IN CT
 Volume Computed Tomography Dose Index (CTDI ) is avol
standardized parameter to measure Scanner Radiation Output
 CTDIvol provides information about the amount of radiation
used to perform the study.
 CTDI is NOT patient dosevol
 CTDI is reported in units of mGy for either a 16-cmvol
(for head exams) or 32-cm (for body exams) diameter.
 AAPM (American Association of Physicts in Medicine)
introduces a parameter known as the Size Specific Dose
Estimate (SSDE) to allow estimation of patient dose based on
CTDI and patient size.vol
 For the same CTDI , a smaller patient will tend to have avol
higher patient dose than a larger patient.

45. Dose Length
Product
Comouted
Tomography
Dose Index