large scale x-ray images taken with the medipix1 chip

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