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Optimising THL-Masks for the Medipix-Quad May, 4 th 2006 Frank Nachtrab

Optimising THL-Masks for the Medipix-Quad May, 4 th 2006 Frank Nachtrab frank.nachtrab@physik.uni-erlangen.de 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, 4 th 2006 Frank Nachtrab

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  1. Optimising THL-Masks for the Medipix-Quad May, 4th 2006 Frank Nachtrab frank.nachtrab@physik.uni-erlangen.de Physikalisches Institut, Abt. IV Friedrich-Alexander-Universität Erlangen

  2. 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

  3. Ring artefacts in CT Problem: variations in lower threshold lead to differing counting behavior for every pixel (‘gain’) → ring artefacts in computed tomography

  4. Equalisation with Noise

  5. Flatfield method: Advantages

  6. Equalisation using Flatfield Images Histogram of Flatfields: THL-maskbit 0, 7; different THS → calculate width and distance of distributions

  7. Optimum THS - Quad Linear fit of right boundary of bit0-distribution vs THS → OptimumTHS (for each Chip on the Quad!)

  8. Mask quality - Definition Countrate independent parameter for mask quality! (lower is better; zero for a perfect detector)

  9. Mask quality Single Chip • All THL-Masks worse for higher thresholds • Flatfieldmasks better by a factor of ~ 1.35

  10. Mask quality Quad

  11. 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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