1. IMAGE RECONSTRUCTION

2. ALGORITHM-A SET OF RULES OR DIRECTIONS FOR GETTING SPECIFIC OUTPUT FROM SPECIFIC INPUT

3. ALGORITHM MUST TERMINATE AFTER FINATE NUMBER OF STEPS

4. CONVOLUTION WITH FILTER
DETECTORS
PRE-PROCESING
REFORMATTED RAW DATA
CONVOLUTION WITH FILTER
IMAGE RECONSTRUCTION ALGORITHM
IMAGE:
STORAGE
DISPLAY
RECORDING
ARCHIVING
RECONSTRUCTED IMAGE

5. IMAGE RECONSTRUCTION PERFORMED BY:
ARRAY PROCESSOR OR PROCESSORS

6. RECONSTRUCTION WHEN ONE OR MORE TECHNICAL FACTORS ARE MODIFIED IS CALLED:
RETROSPECTIVE RECONSTRUCTION

7. FACTORS THAT CAN BE CHANGED DURING RECONSTRUCTION
DFOV
MATRIX
SLICE THICKNESS
SLICE INCREMENTATION
ANGLE

8. SFOV LARGE DFOV

9. SFOV SMALL DFOV
TARGETED (ZOOMED) RECON

10. SFOV VERY SMALL DFOV TARGETED (ZOOMED) RECON

11. USUALLY MATRIX IS PERMANENTLY SET AT 512 X 512
DIFFERENT MATRICES
80 X 80
512 X 512
USUALLY MATRIX IS PERMANENTLY SET AT 512 X 512

12. SLICE THICKNESS
RECONSTRUCTION IN DIFFERENT THICKNESS ONLY POSSIBLE IN THE MULTISLICE UNIT

13. SLICE INCREMENTATION
RECONSTRUCTION IN DIFFERENT SLICE INCREMENTATION POSSIBLE IN SINGLE AND MULTISLICE UNITS

14. INCREMENTATION 2MM 1MM SLICE INCREMENT 2MM 4MM SLICE INCREMENT 2MM
CONTIGUOUS
50% OVERLAP
100% GAP

15. SLICE vs RECONSTRUCTION INCREMENTATION
SLICE THICKNESS
RECON INCREMENT
IMAGE QUALITY

16. TOMO ANGLE 360º
TUBE

17. TOMO ANGLE 180º
TUBE

18. TOMO ANGLE
ANGLE IMAGE QUALITY

19. TYPES OF DATA
MEASUREMENT DATA
RAW DATA
CONVOLVED DATA
IMAGE DATA

20. PREREQUISITE FOR DATA RECONSTRUCTION
DATA AVAILABLE
RAW

21. MEASUREMENT DATA (SCAN DATA)
DATA THAT ARISES FROM DETECTORS. IT NEEDS TO BE PREPROCESSED TO ELIMINATE ARTIFACTS.

22. RAW DATA
IT’S THE RESULT OF SCAN DATA BEING PRE-PROCESSED

23. CONVOLVED DATA
FILTERED BACKPROJECTION IS THE ALGORITHM USED BY MODERN CT.
IT REQUIRES FILTERING AND THEN BACKPROJECTION. RAW DATA IS FILTERED USING MATHEMATICAL FILTER.(CONVOLUTION)
IT REMOVES BLURR. CONVOLUTION CAN ONLY BE APPLIED TO RAW DATA.

24. MATHEMATICAL FILTER CAN ALSO BE CALLED:
KERNEL
ALGORITHM
PASS FILTER

25. TYPES OF FILTERS
SMOOTH
STANDARD
SHARP
EXTRA SHARP

26. TYPES OF FILTERS (SIEMENS)
B20 (SMOOTH)
B40 (STANDARD)
A80 (SHARP)
A91 (VERY SHARP)

27. SMOOTH
SHARP

28. IMAGE DATA (RECONSTRUCTED DATA)
CONVOLVED DATA THAT HAVE BEEN BACKPROJECTED INTO THE IMAGE MATRIX TO CREATE CT IMAGES DISPLAYED ON THE MONITOR.

29. DETECTORS SCAN DATA RAW DATA CONVOLVED DATA DATA PREPROCESSING
CONVOLUTION
CONVOLVED DATA DATA
BACK
PROJECTION

30. BEAM GEOMETRIES AND DATA ACQUSITION
PARALLEL –SLOW
FAN -FASTER

32. Algorithms applicable to CT
Back projection
Iterative methods
Analytic methods

33. BACK PROJECTION
ALSO CALLED SUMMATION METHOD OR LINEAR SUPERPOSITION METHOD

35. Example image of how a cube generates different projections depending on the angle of projection

38. ITERATIVE ALGORITHMS SIMULTANEOUS ITERATIVE RECONSTRUCTION TECHNIQUE
ITERATIVE LEAST SQUARES TECHNIQUE
ALGEBRAIC RECONSTRUCTION TECHNIQUE

39. ITERATIVE RECON DEFINITION
IT STARTS WITH ASSUMPTION AND COMPARES THIS ASSUMPTION WITH A MEASURED VALUE, MAKES CORRECTIONS TO BRING THE TWO VALUES IN AGREEMENT. THIS PROCESS REPEATS OVER AND OVER.

41. ART USED BY HOUNSFIELD IN HIS FIRST EMI BRAIN SCANNER

42. BETTER THAN FILTERED BACK PROJECTION REDUCTION AND NOISE REDUCTION
ITERATIVE TECHNIQUES ARE NOT USED IN TODAY’S COMMERCIAL SCANNERS THEY ARE VERY SLOW
BETTER THAN FILTERED BACK PROJECTION
IN METAL ARTIFACT
REDUCTION AND NOISE REDUCTION

43. ANALYTIC RECONSTRUCTION ALGORITHMS
FOURIER RECONSTRUCTION
FILTERED BACK PROJECTION
USED IN MODERN CT SCANNERS

44. FILTERED BACK-PROJECTION CONVOLUTION METHOD
PROJECTION PROFILE IS FILTERED OR CONVOLVED TO REMOVE THE TYPICAL STAR LIKE BLURRING THAT IS CHARACTERISTIC OF THE SIMPLE BACK PROJECTION.

47. STEPS IN FILTERED BACK PROJECTION
ALL PROJECTION PROFILES ARE OBTAINED
THE LOGARITHM OF DATA IS OBTAINED
LOGARITHMIC VALUES ARE MULTIPLIED BY DIGITAL FILTER
FILTERED PROFILES ARE BACKPROJECTED
THE FILTERED PROJECTIONS ARE SUMMED AND THE NEGATIVE AND POSITIVE COMPONENTS ARE CANCELLED

48. FOURIER RECONSTRUCTION
USED IN MRI
NOT USED IN CT BECAUSE OF COMPLICATED MATHEMATICS

49. ALGORITHM (FILTER) vs NOISE
DETAIL
HIGH PASS FILTER
SHARP
EDGE-ENHANCEMENT
STANDARD
LOW PASS FILTER
SMOOTHING
NOISE

50. RECONSTRUCTION IN SPIRAL CT
FILTERED BACK PROJECTION USED + INTERPOLATION BACAUSE OF THE CONTINUOUS MOVEMENT OF THE PATIENT IN THE Z-DIRECTION.
( TO ELIMINATE MOTION BLURR)

51. RECONSTRUCTION IN MULTISLICE SPIRAL CT
INTERLACED SAMPLING
LONGITUDINAL INTERPOLATION
FAN BEAM RECONSTRUCTION

52. RECONSTRUCTION ALGORITHM COMPARISON
ANALYTIC METHODS ARE FASTER THAN ITERATIVE ALGORITHMS.
FILTERED BACK PROJECTION IS USED IN MODERN CT SCANNERS
ITERETIVE METHODS ARE BETTER THAN FILTERED BACK PROJECTION IN METAL ARTIFACT REDUCTION AND NOISE REDUCTION

53. MPR MULTIPLANAR RECONSTRUCTION (REFORMATTING)

54. IT USES DATA
IMAGE

55. STACKS OF IMAGES ONLY IN ONE PLANE CAN BE USED FOR ONE TYPE OF MPR DIFFERENT PLANE IMAGES CAN NOT BE COMBINED

56. ONLY IMAGES IN ONE PLANE CAN BE COMBINED!

60. CURVED MPR

61. FOR BEST QUALITY IMAGES
USE VOLUMETRIC DATA ACQUSITION
RECON YOUR ORIGINAL THICKER SLICES INTO VERY THIN SLICES (2mm OR 1 mm)
SELECT RECON INCREMENT THAT WOULD CREATE AT LEAST 50% OVERLAP BETWEEN SLICES
EXAMPLE:
2 MM SLICE THICKNESS
1 MM SLICE INCREMENT

62. STAIRCASE ARTIFACT

63. 3-D

64. EXTRUSION IS A MODELING TECHNIQUE THAT GENERATES A 3-D OBJECT FROM A 2 –D PROFILE ON THE COMPUTER SCREEN. IT USES IMAGE DATA TO BUILD 3-D OBJECT

65. EXTRUSION

66. PIXEL AREA B A
A= WIDTH
B= HEIGTH
AREA OF THE PIXEL = A x B

67. VOXEL VOLUME B A C A= WIDTH B= HEIGTH C-DEPTH (SLICE THICKNESS)
VOLUME OF THE VOXEL = A x B x C

68. DATA ACQUSITION FOR 3-D CONVENTIONAL SLICE BY SLICE
VOLUME DATA ACQUSITION

69. PROBLEMS WITH CONVENTIONAL SLICE BY SLICE ACQUISITION IN 3-D GENERATION
MOTION - STAIR-STEP ARTIFACT
MIREGISTRATION

70. STAIR-STEP ARTIFACT

71. SEVERE STAIR-STEP ARTIFACT

72. PROCESSING FOR 3-D SEGMENTATION TRESHOLDING OBJECT DELINEATION
RENDERING

73. SEGMENTATION
PROCESSING TECHNIQUE USED TO IDENTIFY THE STRUCTURE OF INTEREST IN A GIVEN IMAGE. IT DETERMINES WHICH VOXEL ARE PART OF THE OBJECT AND SHOULD BE DISPLAYED AND WHICH ARE NOT AND SHOULD BE DISCARDED.

74. SEGMENTATION

75. THRESHOLDING
METHOD OF CLASSIFYING THE TYPES OF TISSUES REPRESENTED BY EACH OF THE VOXELS. CT NUMBER IS USED TO DETERMINE THIS.

76. TRESHOLDING (IN SEGMENTATION)

77. DELINEATION
BOUNDARY EXTRACTION
VOLUME EXTRACTION

78. DELINEATION

79. RENDERING TECHNIQUES SURFACE RENDERING – SHADED SURFACE DISPLAY (SSD)
VOLUME RENDERING

80. SURFACE RENDERING-SSD
SIMPLER OF THE TWO METHODS. DISPLAYS THE IMAGE ACCORDING TO ITS CALCULATIONS OF HOW THE LIGHT RAYS WOULD BE REFLECTED TO THE VIEWERS EYES.
COMPUTER CREATES INTERNAL REPRESENTATION OF SURFACES

82. ADVANTAGE OF SSD NOT MUCH COMPUTING POWER REQUIRED
ONLY CONTOUR IS USED

83. DISADVANTAGES OF SSD
INFO OF STRUCTURES INSIDE OR BEHIND THE SURFACE IS NOT DISPLAYED!!

84. VOLUME RENDERING
SOPHISTICATED TECHNIQUE. 3-D IMAGES HAVE BETTER QUALITY THAN IN SURFACE RENDERING. USES ENTIRE DATA SET FROM 3-D SPACE. IT REQUIRES MORE COMPUTING POWER.

86. ADVANTAGES OF VOLUME RENDERING (VR)
UNLIKE SSD, VOLUME RENDERING ALLOWS SEEING THROUGH SURFACES. IT ALLOWS THE VIEWER TO SEE BOTH INTERNAL AND EXTERNAL STRUCTURES.

87. DISADVANTAGE/S
IT REQUIRES GREAT COMPUTING POWER – SOPHISTICATED COMPUTER EQUIPMENT

88. MAXIMUM INTENSITY PROJECTION
VOLUME RENDERING 3-D TECHNIQUE THAT IS NOW FREQUENTLY USED IN CTA ( CT ANGIO) IT USES LESS THAN 10% OF DATA IN 3-D SPACE. IT DOES NOT NEED SOPHISTICATED COMPUTING.
IT ORIGINATED IN MRA

89. MIP ALLOWS ONLY THE VOXEL WITH THE BRIGHTEST VALUE TO BE SELECTED

90. VR vs MIP

91. ADVANTAGES OF MIP
NO NEED FOR SOPHISTICATED COMPUTER HARDWARE- IT USES LESS THAN 10% OF DATA

92. DISADVANTAGE/S OF MIP ARTIFACT- STRING OF BEADS
NO SUPERIMPOSED STRUCTURES DEMONSTRATION

93. ARTIFACTS
SSD – MANY FALSE SURFACES
MIP – MIP ARTIFACT
VR - FEW