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IMAGE RECONSTRUCTION - PowerPoint PPT Presentation


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IMAGE RECONSTRUCTION. ALGORITHM -A SET OF RULES OR DIRECTIONS FOR GETTING SPECIFIC OUTPUT FROM SPECIFIC INPUT. ALGORITHM MUST TERMINATE AFTER FINATE NUMBER OF STEPS . DETECTORS. PRE-PROCESING. REFORMATTED RAW DATA. CONVOLUTION WITH FILTER. IMAGE RECONSTRUCTION ALGORITHM. IMAGE: STORAGE

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slide5

DETECTORS

PRE-PROCESING

REFORMATTED RAW DATA

CONVOLUTION WITH FILTER

IMAGE RECONSTRUCTION ALGORITHM

IMAGE:

STORAGE

DISPLAY

RECORDING

ARCHIVING

RECONSTRUCTED IMAGE

history of image reconstruction
HISTORY OF IMAGE RECONSTRUCTION
  • 1917 RADON DEVELOPED MATHEMATICALSOLUTIONS TO THE PROBLEM OF IMAGE RECONSTRUCTION FROM A SET OF PROJECTIONS. UTILIZED IN SOLVING PROBLEMS IN ASTRONOMY AND OPTICS.
  • 1961 FINALLY THESE TECHNIQUES WERE USED IN MEDICINE.
slide7

HOUNSFIELD’S IMAGES—NOISY BECAUSE OF HIS RECONSTRUCTION METHOD. CONVOLUTION BACK PROJECTION USED TO IMPROVE IMAGE QUALITY AND SHORTEN PROCESSING TIME.( USED BY Shepp & Logan)

slide8

ORIGINAL DATA

FILTERED DATA

beam geometries and data acqusition
BEAM GEOMETRIES AND DATA ACQUSITION
  • PARALLEL –SLOW
  • FAN -FASTER
algorithms applicable to ct
Algorithms applicable to CT

Back projection

Iterative methods

Analytic methods

back projection
BACK PROJECTION
  • ALSO CALLED SUMMATION METHOD OR LINEAR SUPERPOSITION METHOD
iterative algorithms
ITERATIVE ALGORITHMS
  • SIMULTANEOUS ITERATIVE RECONSTRUCTION TECHNIQUE
  • ITERATIVE LEAST SQUARES TECHNIQUE
  • ALGEBRAIC RECONSTRUCTION TECHNIQUE
analytic reconstruction algorithms
ANALYTIC RECONSTRUCTION ALGORITHMS
  • FOURIER RECONSTRUCTION
  • FILTERED BACK PROJECTION

USED IN MODERN CT SCANNERS

filtered back projection convolution method
FILTERED BACK-PROJECTIONCONVOLUTION METHOD
  • PROJECTION PROFILE IS FILTERED OR CONVOLVED TO REMOVE THE TYPICAL STAR LIKE BLURRING THAT IS CHARACTERISTIC OF THE SIMPLE BACK PROJECTION.
steps in filtered back projection
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
fourier reconstruction
FOURIER RECONSTRUCTION
  • USED IN MRI
  • NOT USED IN CT BECAUSE OF COMPLICATED MATHEMATICS
fourier transform
FOURIER TRANSFORM
  • RADIOGRAPH –AN IMAGE IN SPATIAL DOMAIN
  • IN FOURIER TRANSFORM IMAGE IN FREQUENCY DOMAIN
  • CAN BE RETRANSFORMED BACK TO SPATIAL DOMAIN BY WITH THE INVERSE FOURIER
types of data
TYPES OF DATA
  • MEASUREMENT DATA
  • RAW DATA
  • CONVOLVED DATA
  • IMAGE DATA
measurement data scan data
MEASUREMENT DATA(SCAN DATA)
  • DATA THAT ARISES FROM DETECTORS. IT NEEDS TO BE PREPROCESSED TO ELIMINATE ARTIFACTS.
raw data
RAW DATA
  • IT’S THE RESULT OF SCAN DATA BEING PRE-PROCESSED
convolved data
CONVOLVED DATA
  • FILTERED BACKPROJECTION IS THE ALGORITHM USED BY MODERN CT.
  • IT REQUIRES FILTERING AND THEN BACKPROJECTION. RAW DATA IS FILTERED USING MATHEMATICAL FILTER OR KERNEL (CONVOLUTION)
  • IT REMOVES BLURR. CONVOLUTION CAN ONLY BE APPLIED TO RAW DATA.
image data reconstructed data
IMAGE DATA(RECONSTRUCTED DATA)
  • CONVOLVED DATA THAT HAVE BEEN BACKPROJECTED INTO THE IMAGE MATRIX TO CREATE CT IMAGES DISPLAYED ON THE MONITOR.
slide41

DETECTORS

PREPROCESSING

SCAN DATA

RAW DATA

CONVOLUTION

CONVOLVED DATA DATA

BACK

PROJECTION

algorithm vs noise
ALGORITHM vs NOISE

DETAIL

EDGE-ENHANCEMENT

STANDARD

SMOOTHING

NOISE

reconstruction in spiral ct
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)

reconstruction in multislice spiral ct
RECONSTRUCTION IN MULTISLICE SPIRAL CT
  • INTERLACED SAMPLING
  • LONGITUDINAL INTERPOLATION
  • FAN BEAM RECONSTRUCTION
reconstruction algorithm comparison
RECONSTRUCTION ALGORITHM COMPARISON
  • ANALYTIC METHODS ARE FASTER THAN ITERATIVE ALGORITHMS.
  • FILTERED BACK PROJECTION IS USED IN MODERN CT SCANNERS