Editing Scanco Administration (section)

==Image Artifacts==
===Ring Artifact===
*Refer to [[Media:Microct_ring_correction.pdf|'''MicroCT Ring Correction''']].


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===Partial Volume Effect===
*Refer to [[Media:Partial_Volume_Effect.pdf|'''Partial Volume Effect''']].


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===Beam Hardening Correction (BHC)===

====Use the right BHC====
*Refer to [[Media:Beam_hardening_correction.pdf|'''Use the right beam hardening correction''']].


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====Understand Scanco BHC====
If you see lines like 'CCD_CORR: Expand BH-corr to1536' etc. etc.: 

then we do a polynomial correction: 
<pre>
$ dir uctd:*bh_coeff*.txt
</pre>
and you see a file with the scanner ID. 

<pre>
--> $ type uctd:UCT_BH_COEFF_60KV_0200HA_3309.TXT

--> 
! Function 9 is Addpolynom
Function:           9 A
0:  3  0.00000000 -0.38599902  0.30870225 -0.06162301
--> 0: for all pixels. 3 --> 3rd degree polynom, with factors: 
x^0 = 0
x^1 = -0.38...
x^2 = 0.308...
x^3 = -0.061...
</pre>

This polynom is added to the PROJECTION value (not the raw counts). 

the BH-corr is doing a 'linearization', e.g. see

http://iospress.metapress.com/content/twcxb9jfk8knhpq2/

for more info. 

The values in the middle of the scan are amplified more - not just because of their position, but because the object is thicker there, thus the projection values are higher, thus the correction term is higher.

<b>NOTE</b> : Linearisation, as used by Scanco, will compensate 'soft-tissue' beam hardening (inside of water phantom appears <b>LESS</b> dense). Bone related beam hardening, e.g. soft tissue near skull appearing <b>MORE</b> dense, will <b>NOT</b> generally be compensated. See Kak and Slaney 'Principles of computerized tomogprahic imaging' and Joseph and Spital J Comp Assist Tomo 1978 vol 2 for more information.


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