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Frank Nachtrab1May, 4 th 2006Medipix2 Meeting Physikalisches Institut Universität Erlangen-Nürnberg Optimising THL-Masks for the Medipix-Quad May, 4 th.

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Presentation on theme: "Frank Nachtrab1May, 4 th 2006Medipix2 Meeting Physikalisches Institut Universität Erlangen-Nürnberg Optimising THL-Masks for the Medipix-Quad May, 4 th."— Presentation transcript:

1 Frank Nachtrab1May, 4 th 2006Medipix2 Meeting Physikalisches Institut Universität Erlangen-Nürnberg Optimising THL-Masks for the Medipix-Quad May, 4 th 2006 Frank Nachtrab Physikalisches Institut, Abt. IV Friedrich-Alexander-Universität Erlangen

2 Frank Nachtrab2May, 4 th 2006Medipix2 Meeting Physikalisches Institut Universität Erlangen-Nürnberg 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 translation stages rotation stage with object plate X-ray tube medipix2 detector MUROS 2.1

3 Frank Nachtrab3May, 4 th 2006Medipix2 Meeting Physikalisches Institut Universität Erlangen-Nürnberg Ring artefacts in CT Problem: variations in lower threshold lead to differing counting behavior for every pixel (gain) ring artefacts in computed tomography

4 Frank Nachtrab4May, 4 th 2006Medipix2 Meeting Physikalisches Institut Universität Erlangen-Nürnberg Equalisation with Noise

5 Frank Nachtrab5May, 4 th 2006Medipix2 Meeting Physikalisches Institut Universität Erlangen-Nürnberg Flatfield method: Advantages Equalisation using electronic noiseflatfield images - spectrum not taken into acount - optimised for THL of noise - only electronic properties - time ~ hours + optimised for given spectrum + optimised for given THL + sensor inhomogenities considered + rather fast method

6 Frank Nachtrab6May, 4 th 2006Medipix2 Meeting Physikalisches Institut Universität Erlangen-Nürnberg Histogram of Flatfields: THL-maskbit 0, 7; different THS calculate width and distance of distributions Equalisation using Flatfield Images

7 Frank Nachtrab7May, 4 th 2006Medipix2 Meeting Physikalisches Institut Universität Erlangen-Nürnberg Optimum THS - Quad Linear fit of right boundary of bit0-distribution vs THS OptimumTHS (for each Chip on the Quad!)

8 Frank Nachtrab8May, 4 th 2006Medipix2 Meeting Physikalisches Institut Universität Erlangen-Nürnberg Mask quality - Definition Countrate independent parameter for mask quality! (lower is better; zero for a perfect detector)

9 Frank Nachtrab9May, 4 th 2006Medipix2 Meeting Physikalisches Institut Universität Erlangen-Nürnberg Mask quality Single Chip All THL-Masks worse for higher thresholds Flatfieldmasks better by a factor of ~ 1.35

10 Frank Nachtrab10May, 4 th 2006Medipix2 Meeting Physikalisches Institut Universität Erlangen-Nürnberg Mask quality Quad standard maskflatfield mask Chip Chip Chip Chip Overall

11 Frank Nachtrab11May, 4 th 2006Medipix2 Meeting Physikalisches Institut Universität Erlangen-Nürnberg 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?

12 Frank Nachtrab12May, 4 th 2006Medipix2 Meeting Physikalisches Institut Universität Erlangen-Nürnberg


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