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Frank Nachtrab1 04. 05. 2006Medipix2-Meeting
Phy
sika
lisch
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nstit
ut
Uni
vers
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Erla
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Optimising THL-Masks for the Medipix-Quad
04. 05. 2006
Frank [email protected]
Physikalisches Institut, Abt. IV Friedrich-Alexander-Universität Erlangen
Frank Nachtrab2 04. 05. 2006Medipix2-Meeting
Phy
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nstit
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Uni
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Medipix2 CT setup in Erlangen
● Three translation stages (1 µm resolution)
● One rotation stage(0.1 degree resolution)
● MUROS 2.1● Distances:
– Focus-detector: 768mm– Focus-object plate: 635mm
● Tungsten X-ray tube: – standard diagnostic tube– tube voltage 40 – 125 kV
translationstagesrotation stage with
object plate
X-ray tube
medipix2detector
MUROS 2.1
Frank Nachtrab3 04. 05. 2006Medipix2-Meeting
Phy
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Ringartefacts in CT
Problem: variations in lower threshold lead to differing counting behavior for every pixel (‘gain’)
-> ringartefacts in computed tomography
Frank Nachtrab4 04. 05. 2006Medipix2-Meeting
Phy
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Uni
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Equalisation with Noise
Frank Nachtrab5 04. 05. 2006Medipix2-Meeting
Phy
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Uni
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Equalisation using Flatfields
Histogram of Flatfields: THL-maskbit 0, 7; different THS→ calculate width and distance of distributions
Frank Nachtrab6 04. 05. 2006Medipix2-Meeting
Phy
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Uni
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Optimum THS
linear fit of right boundary of bit0-distribution vs THS→ OptimumTHS (for every Chip on the Quad!)
Frank Nachtrab7 04. 05. 2006Medipix2-Meeting
Phy
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Uni
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Maskquality - Definition
Countrate independent parameter for maskquality!(lower is better; zero for a perfect detector)
Frank Nachtrab8 04. 05. 2006Medipix2-Meeting
Phy
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Uni
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Maskquality Single Chip
● THL-Masks worse for higher thresholds● Flatfieldmasks better by a factor of ~ 1.35
Frank Nachtrab9 04. 05. 2006Medipix2-Meeting
Phy
sika
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nstit
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Uni
vers
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Maskquality Quad
Standardmask
Flatfieldmask
Chip 1 0.089 0.055
Chip 2 0.082 0.058
Chip 3 0.067 0.057
Chip 4 0.067 0.059
Overall 0.113 0.096
Frank Nachtrab10 04. 05. 2006Medipix2-Meeting
Phy
sika
lisch
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nstit
ut
Uni
vers
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Erla
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