Optimising THL-Masks
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Optimising THL-Masks for the Medipix-Quad May, 4 th 2006 Frank Nachtrab [email protected] Physikalisches Institut, Abt. IV Friedrich-Alexander-Universität Erlangen. medipix2. detector. MUROS 2.1. translation. rotation stage with. stages. object plate.

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Optimising THL-Masks

for the Medipix-Quad

May, 4th 2006

Frank Nachtrab

[email protected]

Physikalisches Institut, Abt. IV

Friedrich-Alexander-Universität Erlangen


Medipix2 ct setup in erlangen

medipix2

detector

MUROS 2.1

translation

rotation stage with

stages

object plate

X-ray tube

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


Ring artefacts in ct
Ring artefacts in CT

Problem: variations in lower threshold lead to differing counting behavior for every pixel (‘gain’)

→ ring artefacts in computed tomography




Equalisation using flatfield images
Equalisation using Flatfield Images

Histogram of Flatfields: THL-maskbit 0, 7; different THS

→ calculate width and distance of distributions


Optimum ths quad
Optimum THS - Quad

Linear fit of right boundary of bit0-distribution vs THS

→ OptimumTHS (for each Chip on the Quad!)


Mask quality definition
Mask quality - Definition

Countrate independent parameter for mask quality!

(lower is better; zero for a perfect detector)


Mask quality single chip
Mask quality Single Chip

  • All THL-Masks worse for higher thresholds

  • Flatfieldmasks better by a factor of ~ 1.35



Outlook
Outlook

  • five different THS Values instead of three → quadratic fit?

  • tune FBK settings after generation of mask for better global homogeneity

  • automate procedure → Pixelman plugin?


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