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Optimising THL Masks for the Medipix Quad

Learn how to enhance Medipix Quad performance by optimizing THL masks using Flatfield method for computed tomography. Discover the advantages of Equalisation with Noise method and explore the process for determining the optimum threshold for each chip on the Quad.

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Optimising THL Masks for the Medipix Quad

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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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