Download IMAGE QUALITY

IMAGE QUALITY
SPATIAL RESOLUTION
CONTRAST RESOLUTION
RADIATION
DOSE
NOISE
IMAGE ARTIFACTS
Resolution in CT
Spatial Resolution
Contrast Resolution
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
MTF
MODULATION TRANSFER
FUNCTION
MOST COMMONLY USED TO
DESCRIBE SPATIAL RESOLUTION
IN CT
MTF
• MTF OF 1 – 100% TRANSFER OF
OBJECT TO IMAGE
• MTF OF 0 – 0% TRANSFER OF OBJECT
TO IMAGE
HIGH CONTRAST PHANTOM
FACTORS AFFECTING
SPATIAL RESOLUTION
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SLICE THICKNESS
FOCAL SPOT SIZE
DETECTOR WIDTH
TYPE OF CONVOLUTION FILTER (KERNEL)
MATRIX SIZE
FOV
SLICE THICKNESS
SLICE THICKNESS
5 MM
S. RESOLUTION
1 MM
FOCAL SPOT SIZE
FOCAL SPOT SIZE
S. RESOLUTION
LARGE FOCAL SPOT = LARGE PENUMBRA (BLURR)
DETECTOR WIDTH
DETECTOR WIDTH
S. RESOLUTION
TYPE OF CONVOLUTION
FILTER
SHARP KERNEL
SMOOTH
S. RESOLUTION
SHARP
MATRIX SIZE
MATRIX SIZE
80 X 80
S. RESOLUTION
512 X 512
DFOV SIZE
DFOV
20CM
S. RESOLUTION
10CM
CONTRAST RESOLUTION
• SENSITIVITY OF THE SYSTEM
• LOW CONTRAST RESOLUTION
• LOW CONTRAST DETECTIBILITY
LOW CONTRAST
RESOLUTION
( TISSUE RESOLUTION)
• THE ABILITY OF AN IMAGING
SYSTEM TO DEMONSTRATE SMALL
CHANGES IN TISSUE CONTRAST
CONTRAST RESOLUTION
• SENSITIVITY OF THE SYSTEM
• LOW CONTRAST RESOLUTION
• LOW CONTRAST DETECTIBILITY
CONTRAST RESOLUTION
PHANTOM
FACTORS AFFECTING LOW
CONTRAST RESOLUTION
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PHOTON FLUX
SLICE THICKNESS
PATIENT SIZE
DETECTOR SENSITIVITY
RECONSTRUCTION ALGORITHM
IMAGE DISPLAY
QUANTUM NOISE
PHOTON FLUX (INTENSITY)
PHOTON FLUX
mAs
kVp
C. RESOLUTION
P. FLUX
P. FLUX
LOW TECHNIQUE
ADEQUATE TECHNIQUE
SLICE THICKNESS
SLICE THICKNESS
8 mm
C. RESOLUTION
5 mm
10 mm – 100 PHOTONS
5 mm – 50 PHOTONS
PATIENT SIZE
PATIENT SIZE
NORMAL
C. RESOLUTION
LARGE
DETECTOR SENSITIVITY
DETECTOR SENSITIVITY
C. RESOLUTION
TYPE OF CONVOLUTION
FILTER
SMOOTH KERNEL
SMOOTH
C. RESOLUTION
SHARP
IMAGE DISPLAY
MONITOR RESOLUTION
C. RESOLUTION
QUANTUM NOISE
QUANTUM NOISE
HIGH NOISE
C. RESOLUTION
LOW NOISE
NOISE IN CT
• FLUCTUATION OF
CT# BETWEEN
POINTS IN THE
IMAGE FOR A
SCAN OF
UNIFORM
MATERIAL SUCH
WATER.
NOISE SOURCES IN CT
• QUANTUM NOISE – X-RAY INTENSITY AT THE
DETECTORS
• MATRIX SIZE
• DFOV
• SLICE THICKNESS
• CONVOLUTION FILTER TYPE
• PITCH
QUANTUM NOISE –
CONTROLLED BY THE
TECHNOLOGIST
• mA
• Time
• kVp
NOISE
NOISE
• QUANTUM
(STATISTICAL) –
CONTROLLED BY
THE
TECHNOLOGIST
• ELECTRONIC –
INHERENT IN THE
EQUIPMENT
QUANTUM NOISE –
CONTROLLED BY THE
TECHNOLOGIST
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DFOV
MATRIX
COLLIMATION
FILTER SPATIAL
FREQUENCY
• PITCH
NOISE
DOSE
vs
IMAGE QUALITY
• RADIATION DOSE
IMAGE QUALITY