IMAGE QUALITY. SPATIAL RESOLUTION CONTRAST RESOLUTION NOISE IMAGE ARTIFACTS RADIATION DOSE

IMAGE QUALITY

SPATIAL RESOLUTION CONTRAST RESOLUTION

NOISE

IMAGE ARTIFACTS

RADIATIONDOSE

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

MTFMODULATION 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

• SLICE THICKNESS

• FOCAL SPOT SIZE

• DETECTOR WIDTH

• TYPE OF CONVOLUTION FILTER (KERNEL)

• MATRIX SIZE

• FOV

SLICE THICKNESS

SLICE THICKNESS S. RESOLUTION

5 MM 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 S. RESOLUTION

SMOOTH SHARP

MATRIX SIZE

MATRIX SIZE S. RESOLUTION

80 X 80 512 X 512

DFOV SIZE

DFOV S. RESOLUTION

20CM 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

• PHOTON FLUX

• SLICE THICKNESS

• PATIENT SIZE

• DETECTOR SENSITIVITY

• RECONSTRUCTION ALGORITHM

• IMAGE DISPLAY

• QUANTUM NOISE

PHOTON FLUX (INTENSITY)

PHOTON FLUX C. RESOLUTION

mAs P. FLUXkVp P. FLUX

LOW TECHNIQUE ADEQUATE TECHNIQUE

SLICE THICKNESS

SLICE THICKNESS C. RESOLUTION

8 mm 5 mm

10 mm – 100 PHOTONS 5 mm – 50 PHOTONS

PATIENT SIZE

PATIENT SIZE C. RESOLUTION

NORMAL LARGE

DETECTOR SENSITIVITY

DETECTOR SENSITIVITY C. RESOLUTION

TYPE OF CONVOLUTION FILTER

SMOOTH KERNEL C. RESOLUTION

SMOOTH SHARP

IMAGE DISPLAY

MONITOR RESOLUTION C. RESOLUTION

QUANTUM NOISE

QUANTUM NOISE C. RESOLUTION

HIGH NOISE 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

• DFOV

• MATRIX

• COLLIMATION

• FILTER SPATIAL FREQUENCY

• PITCH

NOISE

DOSE vs

IMAGE QUALITY

• RADIATION DOSE IMAGE QUALITY