IMAGE RECONSTRUCTION

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

ALGORITHM MUST TERMINATE AFTER FINATE NUMBER OF STEPS

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

HISTORY OF IMAGE RECONSTRUCTION 1917 RADON DEVELOPED MATHEMATICAL SOLUTIONS TO THE PROBLEM OF IMAGE RECONSTRUCTION FROM A SET OF PROJECTIONS. UTILIZED IN SOLVING PROBLEMS IN ASTRONOMY AND OPTICS FINALLY THESE TECHNIQUES WERE USED IN MEDICINE.

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)

ORIGINAL DATAFILTERED DATA

CONVOLUTION BACK PROJECTION DEVELOPED BY: RAMCHANDRAN LAKSHMINARAYANAN

BEAM GEOMETRIES AND DATA ACQUSITION PARALLEL –SLOW FAN -FASTER

Algorithms applicable to CT Back projectionIterative methodsAnalytic methods

BACK PROJECTION ALSO CALLED SUMMATION METHOD OR LINEAR SUPERPOSITION METHOD

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

INCOMPLETE BACK- PROJECTION

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

ART USED BY HOUNSFIELD IN HIS FIRST EMI BRAIN SCANNER

ITERATIVE TECHNIQUES ARE NOT USED IN TODAY’S COMMERCIAL SCANNERS

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

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.

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 USED IN MRI NOT USED IN CT BECAUSE OF COMPLICATED MATHEMATICS

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 MEASUREMENT DATA RAW DATA CONVOLVED DATA IMAGE DATA

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

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

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

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

ALGORITHM vs NOISE DETAIL NOISE STANDARD SMOOTHING EDGE-ENHANCEMENT

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 INTERLACED SAMPLING LONGITUDINAL INTERPOLATION FAN BEAM RECONSTRUCTION

RECONSTRUCTION ALGORITHM COMPARISON ANALYTIC METHODS ARE FASTER THAN ITERATIVE ALGORITHMS. FILTERED BACK PROJECTION IS USED IN MODERN CT SCANNERS