Large scale x-ray images taken with the Medipix1 chip

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Large scale x-ray images taken with the Medipix1
chip
Karl-Friedrich Pfeiffer Physikalisches Institut,
Abt. 4 Universität Erlangen-Nürnberg Workgroup
SPOC
Single PhOton Counting
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Overview

• The Medipix1 chip
• Experimental setup
• Large Images 1 'Move and Tile'Measurement and
  Simulation
• Large Images 2 'Tile and Move'Measurement and
  Simulation
• DQE Measurements
• Summary

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The Medipix1 chip

• Pixelated solid state hybrid detector for single
  photon counting
• 64 x 64 Pixel, size 170mm Þ active area 10.88 x
  10.88 mm2
• Semiconductor sensor layer bump-bonded to the
  pixelated read-out electronics chip
• Sensor layer e.g. 300mm Si, but other materials
  (GaAs, Cd(Z)Te...) can be used as well
• Developed within the framework of the Medipix1
  collaboration

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Experimental setup

• Complete imaging process controlled by computer 1
• Data acquisition done with Medisoft software
  (developed in the Medipix collaboration)
• (Semi-)automated processing of acquired data

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Large Images 1 'Move and Tile'

• Make single exposure with single detector
• Move detector to next position
• Make another exposure
• Repeat until the whole area is covered
• Merge all single exposures to get one large tiled
  image

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Large Images 1 Measurement
5x5 single exposures, 10 pixels overlap
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Comparison Measurement - Simulation
Object Siemensstern 0.05mm Pb in 2mm PMMA Ø
4.5cm

• Contrast ratio
• measurement -simulation
• 0.996
• 0.978

• Contrast Pb -Air0.965
• Contrast Pb-PMMA0.941

• Contrast Pb -Air0.969
• Contrast Pb-PMMA0.962

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Large Images 2 'Tile and Move'

• Tile several detectors to make an array
• Take large picture (with gaps)
• Move array to next position
• Take another picture
• Repeat to cover all gaps
• Merge pictures to get one large image without
  gaps and with high photon statistics

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Large Images 2 Measurement
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Comparison Measurement - Simulation
Object Siemensstern 0.05mm Pb in 2mm PMMA Ø
4.5cm

• Contrast ratio
• measurement -simulation
• 0.988
• 0.964

• Contrast Pb -Air0.954
• Contrast Pb-PMMA0.928

• Contrast Pb -Air0.966
• Contrast Pb-PMMA0.963

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Improved 'Tile and Move'

• If it is possible to tile several detecors
  without gaps (e.g. with the Medipix2 chip)
• Þ Tile detectors to get detector bars'
  two pictures are sufficient to cover all
  gaps
• Þ even faster less dose!

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DQE Definition

• DQE Detective Quantum Efficiency
• SNR Signal-to-Noise-Ratio
• in SNR of incoming radiation field ( ?N )
• out SNR of the image
• f f(x,y) Spatial frequency

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Calculation of the DQE
? System gain factor MTF Modulation Transfer
Function NPS Noise Power Spectrum ltEgt Mean
photon energy ?0 Incoming energy fluence
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DQE Measurement

• MTF(f) measurementline pair phantom
• NPSout measurementflat field images
• ... some lenghty calculations ...
• Þ DQE(f)

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MTF results
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First DQE results
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Summary

• There are basically two ways to get large field
  images
• 1) 'Move and Tile' single detector, flexible,
  but takes quite a long time and high dose Þ 'Lab
  Method'
• 2) 'Tile and Move' quite fast, but requires
  several detectors Þ 'Standard Imaging Method'
• The MTF and DQE of a Medipix1 chip with a 300mm
  Si sensor layer was determined
• We are looking forward to the Medipix2 chip

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Thanks to

• Prof. G. Anton1
• Ch. Bert1 D. Niederlöhner1
• J. Giersch1
• M. Hoheisel2 L. Bätz2 (for the DQE
  calculations)
• Medipix Collaboration
• B. Mikulec3

1Universität Erlangen 2 Siemens 3 CERN
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Phantoms used
Siemensstern
Line pair phantom
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Background picture blown fuse