CT SCAN : IMAGE QUALITY & ARTIFACTS

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 Image quality :- 

Ct image quality is mainly controlled by four factors, namely -


→Spatial resolution

 spatial resolution is the ability to discriminate between adjacent objects, that is expressed in lp/cm 
It depends on pixel size, detector size, choice of image reconstruction filter and sampling frequency.
The range of spatial resolution in CT is 5 to 15 lp/cm.

→Noise 

Noise is the fundamental limit to the quality of CT image. It reduces contrast resolution of small objects.
There are three sources of noise- 
1 quantum noise 
2 electronic noise
3 structural noise
 The typical noise level in CT scan is 3 HU.

→contrast  

Ct contrast is the difference in the HU values between the adjacent tissues.
It increase as tube voltage decreases, not affected by tube current or scan times.

→artifacts

Artifacts - 

Artifacts are the one which not only degrade image quality, but also leads to wrong or miss diagnosis.
The typical artifacts in CT image are as follows:
Motion artifacts
Streak artifacts
Beam- hardening artifacts
Ring artifacts
Partial volume artifacts
Spiral artifacts 
Rod artifacts





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