Frank Nachtrab1 04. 05. 2006Medipix2-Meeting

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Optimising THL-Masks for the Medipix-Quad

04. 05. 2006

Frank Nachtrabfrank.nachtrab@physik.uni-erlangen.de

Physikalisches Institut, Abt. IV Friedrich-Alexander-Universität Erlangen

Frank Nachtrab2 04. 05. 2006Medipix2-Meeting

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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

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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

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Equalisation with Noise

Frank Nachtrab5 04. 05. 2006Medipix2-Meeting

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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

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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

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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

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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

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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

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