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Published byLesley Sherman Modified over 8 years ago
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IMAGE QUALITY
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SPATIAL RESOLUTION CONTRAST RESOLUTION NOISE IMAGE ARTIFACTS RADIATION DOSE
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QUALITY MEASUREMENT METHODS PSF- POINT SPREAD FUNCTION LSF- LINE SPREAD FUNCTION CTF – CONTRAST SPREAD FUNCTION MTF- MODULATION TRANSFER FUNCTION
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MTF MODULATION TRANSFER FUNCTION MOST COMMONLY USED TO DESCRIBE SPATIAL RESOLUTION IN CT
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MTF MTF OF 1 – 100% TRANSFER OF OBJECT TO IMAGE MTF OF 0 – 0% TRANSFER OF OBJECT TO IMAGE
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Spatial frequency Lp/cm
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Spatial Frequency LARGE OBJECTS – LOW S.F. SMALL OBJECTS – HIGH S.F.
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SPATIAL FREQUENCY 1 5
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ABSOLUTE SIZE OF AN OBJECT IN CT IT’S EQUAL TO THE RECIPROCAL OF THE SPATIAL FREQUENCY CT SCANNER SPATIAL FREQUENCY- 15 lp/cm. WHAT SIZE OF AN OBJECT CAN THE SCANNER RESOLVE 1/15 = 0.06 cm/lp= 0.6 mm/lp 0.6 /2 = 0.3 mm object
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Resolution in CT Spatial ResolutionContrast Resolution
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SPATIAL RESOLUTION DEGREE OF BLURRING IN THE IMAGE MEASURE OF THE ABILITY TO DISCRIMINATE OBJECTS OF VARYING DENSITY A SMALL DISTANCE APART AGAINST A UNIFORM BACKGROUND
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GEOMETRIC FACTORS F. SPOT SIZE BLURR APERTURE SIZE ( COLLIMATION) BLURR SLICE THICKNESS BLURR
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PARTIAL VOLUME EFFECT 10MM SLICE THICKNESS SPREADS 2MM OBJECT OVER THE ENTIRE SLICE THICKNESS
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# of projections S. resolution
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ALGORITHM vs NOISE DETAIL NOISE STANDARD SMOOTHING EDGE-ENHANCEMENT
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SPATIAL RESOLUTION AT HIGH CONTRAST HIGH CONTRAST RESOLUTION
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DISPLAY RESOLUTION THE # OF PIXELS PER HORIZONTAL AND VERTICAL DIMENSIONS OF THE MATRIX ON THE MONITOR SCREEN OR FILM SHEET MATRIX SIZE DISPLAY RESOLUTION
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DISPLAY RESOLUTION
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HIGH RESOLUTION CT SLICE- 1 – 2 MM REDUCTION OF PARTIAL VOLUME ARTIFACT USE OF HIGH SPATIAL FREQ. ALGORITHM ( GOOD DETAIL) USE OF SMALL FOV ( SMALLER PIXEL)
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RECONSTRUCTION ( TARGETING) vs MAGNIFICATION IN SPATIAL RESOLUTION RECONSTRUCTION - VERY LITTLE DIFFERENCE MAGNIFICATION – SIGNIFICANT DIFFERENCE, SPATIAL RESOLUTION
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CONTRAST RESOLUTION SENSITIVITY OF THE SYSTEM LOW CONTRAST RESOLUTION LOW CONTRAST DETECTIBILITY
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LOW CONTRAST RESOLUTION ( TISSUE RESOLUTION) THE ABILITY OF AN IMAGING SYSTEM TO DEMONSTRATE SMALL CHANGES IN TISSUE CONTRAST
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FACTORS AFFECTING LOW CONTRAST RESOLUTION PHOTON FLUX SLICE THICKNESS PATIENT SIZE DETECTOR SENSITIVITY RECONSTRUCTION ALGORITHM IMAGE DISPLAY IMAGE RECORDING QUANTUM NOISE
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CONTRAST RESOLUTION PHANTOM
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PHOTON FLUX (P.F.) kVp P.F. mAs P.F. KVP, mAs C. RESOLUTION
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PATIENT SIZE PHOTON FLUX PATIENT SIZE C. RESOLUTION
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SLICE THICKNESS C. RESOLUTION SLICE THICKNESS C. RESOLUTION
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DETECTOR SENSITIVITY C. RESOLUTION DETECTOR SENSITIVITY C. RESOLUTION
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LOW CONTRAST RESOLUTION LOW SPATIAL FREQUENCY ALGORITHM
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ALGORITHM vs NOISE DETAIL NOISE STANDARD SMOOTHING EDGE-ENHANCEMENT
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QUANTUM NOISE C. RESOLUTION QUANTUM NOISE C. RESOLUTION
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NOISE IN CT FLUCTUATION OF CT# BETWEEN POINTS IN THE IMAGE FOR A SCAN OF UNIFORM MATERIAL SUCH WATER.
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