Download ppt - IEAP CTU Prague 8 th December, 2004Tomáš Holý Neutron tomography with Medipix-2 Tomáš Holý, Jan Jakůbek, Stanislav Pospíšil, Josef Uher

8th December, 2004 Tomáš Holý IEAP CTU Prague

Neutron tomography with Medipix-2

Tomáš Holý, Jan Jakůbek, Stanislav Pospíšil, Josef Uher

8th December, 2004 Tomáš Holý

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Outline

Tomography principles

Filtered backprojection algorithm

Adaptation of Medipix-2 for neutron detection

Examples of micro-tomography reconstructions

Comparison with Medipix-1

Conclusion and outlook


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Tomography measurement

Medipix-2 detector

Sample

Step motor

Slice of sample and its projection on detector

Parallel neutron beam


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Neutron transmission

Neutron beam intensity attenuation:a(x,y) – attenuation coefficient function

path

dsyxa

eII),(

0

Sample attenuating the beam

Projection on detector plane

I

Idsyxa

path

0log),( Reconstruction of a(x,y)


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Parallel projections

Projection P(t)

x

y

Object slice a(x,y)

Radon transform of a(x, y)

Projection at

dxdytyxyxatP )sincos(),()(


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Filtered back-projection algorithm

Based on Fourier Slice Theorem: S(w) is Fourier transform of projection P(t) A(u, v) is Fourier transform of a(x,y)

sin,cos wwAwS

Projections are filtered with ramp filter |w| and backprojected along angle to slice reconstruction

Additional smoothing of projections can improve noise level

Filtered projections

Reconstruction


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Filtered back-projection algorithm

dyxQ

ddwewwS

ddwewwF

wdwdwFyxf

yxwi

yxwi

yxwi

0

0

)sincos(2

0

)sincos(2

2

0 0

)sincos(2

)sincos(

)(

),(

e),(),(


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Medipix-2 device with converter

neut

ron

triton

alpha

Reaction: 6Li + n (2.05 MeV) + 3H (2.72 MeV)Cross section: 940 barns (0.0253 eV)

256x256 pixels, 55x55 µm2 each, active area 1,98 cm2

Each pixel contains 2 discriminators, 2x3-bit thresholds adjustments and 13-bit pseudo-random counter300 µm thick silicon detector Converter layer (6Li)

Silicon detector

Bump bonding

Readout chip


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Thermal neutron source

NEUTRA station of spallation neutron source SINQ in Paul Scherrer Institute, Villigen, Switzerland

Intensity about 107 neutrons/cm2s at proton accelerator current of 1 mA and proton energy of 590 MeV

Beam cross section is 40 cm in diameter


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Lemo connectorReconstruction from 100 projectionsEach projection 150 s


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PotentiometerReconstruction from 100 projectionsEach projection 150 s


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ToothReconstruction from 100 projectionsEach projection 150 s


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Cartridge – comparison with Medipix-1

Reconstruction from 48 projectionsEach projection 90 s

Medipix-164x64 pixelsEach pixel 170x170 µm2

300 µm thick silicon detector

Neutron sourceHorizontal channel of the LVR-15 nuclear research reactor at Nuclear Physics Institute of the Czech Academy of Sciences at Rez near Prague.Intensity ~107 neutrons/cm2s (at reactor power of 8MW)Beam Cross section: 4 mm x 60 mmThe divergence of the beam is < 0.5°


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Cartridge – Medipix-1 with X-rays

Reconstruction from 48 projectionsEach projection 30 s

Medipix-164x64 pixelsEach pixel 170x170 µm2


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Cartridge – Medipix-2Reconstruction from 100 projectionsEach projection 150 s


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Conclusion and outlook

Medipix-2 offers excellent properties for neutron micro-tomography – very good spatial resolution and unlimited dynamic range

Tomography expertiments requires synchronization of several devices. In Medisoft4 is no way to synchronize actions with other programs => complete acqusition is necessary => time demanding offline analysis

It is necessary to develop flexible software for acquistion control allowing other application to access Medipix-2 device and providing interprocess synchronization


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Basic user interface (MpxCtrlUI.dll)

Data sharing and process synchronization plugin

Custom plugins (experiment specific)

Communication plugins

Client interface library

User application

Plugins

ArchitectureMuros + NI card

Muros HW library (MpxHw.dll)

Control library (MpxCtrl.dll)

Manager (MpxManager.dll)

Medipix Loader (MpxLoader.exe)

USB HW library, … Dummy HW library, …

USB

User application

Hardware independent access to MedipixAuto-initialization and chipboard configuration handlingMultiple acquisition handling (custom size stream/frame buffer, integral buffer, thread-level buffer synchronization)Callback function registrationImplemented in C++, limited number of platform dependent calls, no MFC

Hardware independent access to MedipixAuto-initialization and chipboard configuration handlingMultiple acquisition handling (custom size stream/frame buffer, integral buffer, thread-level buffer synchronization)Callback function registrationImplemented in C++, limited number of platform dependent calls, no MFC

Plugin management (plugin registration, initialization, …)Provides access to MpxCtrl library, Windows messages (for convenient MFC plugins usage), tray menuProvides communication between pluginsImplemented in C++ Load-time dynamic linking of MpxCtrl.dllRun-time dynamic linking of registered plugins

Plugin management (plugin registration, initialization, …)Provides access to MpxCtrl library, Windows messages (for convenient MFC plugins usage), tray menuProvides communication between pluginsImplemented in C++ Load-time dynamic linking of MpxCtrl.dllRun-time dynamic linking of registered pluginsMedipix Manager initializationTray menu buildingForwards all incoming Win messages to Medipix ManagerLoad-time dynamic linking of MpxManager.dllImplemented in C++, MFC

Medipix Manager initializationTray menu buildingForwards all incoming Win messages to Medipix ManagerLoad-time dynamic linking of MpxManager.dllImplemented in C++, MFC

Basic user interface for Medipix Control

Chipboard configuration management

Basic data acquisition control

Simple data previewCustom plugin optionally loaded by managerLoad-time dynamic linking of MpxManager.dllImplemented in C++ (MFC regular DLL)

Basic user interface for Medipix Control

Chipboard configuration management

Basic data acquisition control

Simple data previewCustom plugin optionally loaded by managerLoad-time dynamic linking of MpxManager.dllImplemented in C++ (MFC regular DLL)

Exclusive access to HW Hardware detection and diagnosticsExports set of basic functions for hardware independent access to MedipixSingle threadedImplementation in C

Exclusive access to HW Hardware detection and diagnosticsExports set of basic functions for hardware independent access to MedipixSingle threadedImplementation in C