large scale x-ray images taken with the medipix1 chip
DESCRIPTION
Medipix Collaboration. Large scale x-ray images taken with the Medipix1 chip. Karl-Friedrich Pfeiffer Physikalisches Institut, Abt. 4 Universität Erlangen-Nürnberg Workgroup SPOC *. * S ingle P h O ton C ounting. Overview. The Medipix1 chip Experimental setup - PowerPoint PPT PresentationTRANSCRIPT
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 1 IWORID 4, September 2002
Large scale x-ray images taken with the Medipix1 chip
Karl-Friedrich PfeifferPhysikalisches Institut, Abt. 4
Universität Erlangen-Nürnberg
Workgroup SPOC*Medipix Collaboration
*Single PhOton Counting
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 2 IWORID 4, September 2002
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
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 3 IWORID 4, September 2002
The Medipix1 chip
Pixelated solid state hybrid detector for single photon counting
64 x 64 Pixel, size 170m active area 10.88 x 10.88 mm2
Semiconductor sensor layer bump-bonded to the pixelated read-out electronics chip
Sensor layer: e.g. 300m Si, but other materials (GaAs, Cd(Z)Te...) can be used as well
Developed within the framework of the Medipix1 collaboration
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 4 IWORID 4, September 2002
Experimental setup
Computer 1:main control
Computer 2:data acquisition
Translation stages
X-ray generatorMUROS1 board &Medipix1 chip
Complete imaging process controlled by computer 1 Data acquisition done with Medisoft software (developed in the
Medipix collaboration) (Semi-)automated processing of acquired data
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 5 IWORID 4, September 2002
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
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 6 IWORID 4, September 2002
Large Images 1: Measurement
5x5 single exposures,10 pixels overlap
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 7 IWORID 4, September 2002
Comparison Measurement - Simulation
Object:„Siemensstern“0.05mm Pb in2mm PMMA
Ø 4.5cm
Contrast Pb -Air:0.965
Contrast Pb-PMMA:0.941
Contrast ratio measurement -simulation:
0.996
0.978
Contrast Pb -Air:0.969
Contrast Pb-PMMA:0.962
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 8 IWORID 4, September 2002
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
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 9 IWORID 4, September 2002
Large Images 2: Measurement
3 images,4 x 4 tiles each
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 10 IWORID 4, September 2002
Comparison Measurement - Simulation
Object:„Siemensstern“0.05mm Pb in2mm PMMA
Ø 4.5cm
Contrast Pb -Air:0.954
Contrast Pb-PMMA:0.928
Contrast ratio measurement -simulation:
0.988
0.964
Contrast Pb -Air:0.966
Contrast Pb-PMMA:0.963
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 11 IWORID 4, September 2002
Improved 'Tile and Move'
If it is possible to tile several detecors without gaps (e.g. with the Medipix2 chip):
Tile detectors to get ’detector bars': two pictures are sufficient to cover all gaps
even faster & less dose!
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 12 IWORID 4, September 2002
DQE Definition
DQE: Detective Quantum Efficiency
SNR: Signal-to-Noise-Ratio
1 in: SNR of incoming radiation field (~ N )
2 out: SNR of the image f = f(x,y): Spatial frequency
DQE f SNR
out
2 f
SNRi n
2
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 13 IWORID 4, September 2002
Calculation of the DQE
: System gain factorMTF : Modulation Transfer FunctionNPS : Noise Power Spectrum<E> : Mean photon energy0 : Incoming energy fluence
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 14 IWORID 4, September 2002
DQE Measurement
MTF(f) measurement:line pair phantom
NPSout
measurement:
flat field images
... some lenghty calculations ...
DQE(f)
15.5cm
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 15 IWORID 4, September 2002
MTF: results
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 16 IWORID 4, September 2002
First DQE results
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 17 IWORID 4, September 2002
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 'Lab Method'
2) 'Tile and Move': quite fast, but requires several detectors 'Standard Imaging Method'
The MTF and DQE of a Medipix1 chip with a 300m Si sensor layer was determined
We are looking forward to the Medipix2 chip
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 18 IWORID 4, September 2002
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
2Siemens
3CERN
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 19 IWORID 4, September 2002
Phantoms used:
Siemensstern
Line pair phantom
K.-F. Pfeiffer, PI4Universität Erlangen-Nürnberg 20 IWORID 4, September 2002
Background picture: blown fuse