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C. David, IEEE Conference, Rome, 21.10.2004

LMNLMN

SLSSLS

Phase Contrast X-Ray Radiography and Tomography Based on a Grating Interferometer

C. David, T. Weitkamp, A. DiazLaboratory for Micro- and Nanotechnology (LMN), Paul Scherrer Institut, Switzerland

F. Pfeiffer, M. Stampanoni, J.F. van der Veen Swiss Light Source (SLS), Paul Scherrer Institut, Switzerland


X-rays for medical imaging

• Minimizing the radiation dose is an important issue – especially in mammography

• low absorption contrast => large dose required to obtain sufficiently good S/N

• low applied photon energy (Mo anodes) • screening submits a large number of healthy patients to radiation dose


Improving contrast

Source Sample Detector


Improving contrast


efficiency, size, resolution


Improving contrast


spectrum, power, coherence



Improving contrast


spectrum, power, coherence


contrast mechanism


Phase contrast vs. amplitude contrast

n = 1 – + i

x-rays



n = 1 – + i

x-rays



n = 1 – + i

x-rays



Example:• 20 keV• Organic sample (polymer, biological, medical…) .• 50 m thickness

n = 1 – + i

x-rays



Example:• 20 keV• Organic sample (polymer, biological, medical…) .• 50 m thickness only 0.2 % absorption, but - phase shift

n = 1 – + i

x-rays



Example:• 20 keV• Organic sample (polymer, biological, medical…) .• 50 m thickness only 0.2 % absorption, but - phase shift

n = 1 – + i

x-rays

+



Example:• 20 keV• Organic sample (polymer, biological, medical…) .• 50 m thickness only 0.2 % absorption, but - phase shift much higher contrast less dose required

n = 1 – + i

x-rays

+


Hard x-ray interferometry

Bonse-Hart Interferometer (since 1965)

detector

Object




detector

• Object beam and reference beam are generated by Bragg reflections on thin Si crystals

• The interference of both beams gives a phase image

Object




detector

• optical path length difference needs to be stable to a fraction of a wavelengths

picometer stability required

cannot be scaled up

• Object beam and reference beam are generated by Bragg reflections on thin Si crystals

• The interference of both beams gives a phase image

Object


Propagation methods – edge contrast


• phase shift greatly enhances contrast of edges

• can be used to retrieve phase information

• requires high degree of transverse coherence (i.e. small source size)

• cannot be scaled up to large fields of view (required detector resolution)

Propagation methods – edge contrast


50 nm

Grating x-ray interferometry


beam-splitter phase grating

s




s




interference pattern

s




analyzer amplitude grating


camera






Moiré fringes

camera






camera






camera






camera






camera






camera






camera






camera






camera






camera






camera






camera






camera






phase object

camera






phase object

camera






phase object

camera




analyzer amplitude gratingphase object


camera






phase object

camera



Differential phase contrast imaging!

camera




phase object



4 µm4 µm 4 µm

Phase grating (silicon, p = 4 µm)

•Si-110 wet-etched•Depth of structures chosen so that

phase shift is π no zeroth order

The gratings


4 µm4 µm 4 µm

Absorption grating (Au in silicon, q = 2 µm)

•Au in gaps of Si grating•Grown electrochemically•Period is half that of the phase grating

The gratings

Phase grating (silicon, p = 4 µm)

4 µm4 µm

•Si-110 wet-etched•Depth of structures chosen so that

phase shift is π no zeroth order


polystyrene spheres Ø 100 and 200 µm

Photon energy: 12.4 keVp = 4 µm q = 2 µm

BM 5, ESRF, Dec. 2002


Absorption contrast andedge contrast

Interferometric phase contrast




Differential phase contrast



Can be integrated to yield projected phase shift of sample

Suited for tomographic reconstruction


Differential phase contrast Phase contrast


Edge contrast vs. Interferometric contrast

Non-interferometric

Absorption andEdge contrast

Tomogram

Projection0.5mm


Interferometric phase contrastNon-interferometric

Phase gradientAbsorption andEdge contrast Phase

Tomogram

Projection Projection

Tomogram

Projection

ID19, ESRF, June 200414.4 keV

0.5mm

Edge contrast vs. Interferometric contrast


0.5mm

C. David, IEEE Conference, Rome, 21.10.20041mm

0.5 mm

C. David, IEEE Conference, Rome, 21.10.20041mm

0.5 mm


Polychromatic radiation


camera




phase object

λ1



camera




phase object

λ1

λ2



camera




phase object

λ1

λ2



camera




phase object

λ1

λ2



Pink-beam phase tomography

• SLS wiggler• No monochromator• Zr absorption filter 100 µm• Camera scintillator YAG:

Y absorption edge at 17.0 keVacts as high-pass filter

• Mean energy E = 17.5 keVBandwidth ΔE ≈ 1 keV

Beam conditioning:



Three fibers• Polyamide Ø 225 µm• Boron Ø 200 µm, core: W Ø 10 µm• PBT Ø 190 µm

• SLS wiggler• No monochromator• Zr absorption filter 100 µm• Camera scintillator YAG:

Y absorption edge at 17.0 keVacts as high-pass filter

• Mean energy E = 17.5 keVBandwidth ΔE ≈ 1 keV

Beam conditioning:

Sample:




Sample:

Edge contrast




Sample:

Differential phase contrast

Edge contrast




Sample:


Edge contrast




Sample:


Edge contrast Edge contrasttomogram

Phase contrasttomogram




Required transverse coherence


s camera

d



s camera

dIn our experiments:

E = 17.5 keV, => = 0.07nm

d = 28mm, => s = 1m



s camera


E = 17.5 keV, => = 0.07nm

d = 28mm, => s = 1m

Transverse coherence length c:

c = * p/s

p: source distance, e.g. 2m s: source size, e.g. 100m



s camera


E = 17.5 keV, => = 0.07nm

d = 28mm, => s = 1m

Transverse coherence length c:

c = * p/s = 1.4m

p: source distance, e.g. 2m s: source size, e.g. 100m



Summary


Summary

• There is a large potential to reduce the x-ray dose in medical imaging by exploiting the phase shifting property of matter rather than the absorption


Summary


• Grating interferometry offers advantages compared to other phase imaging methods :


Summary


• Grating interferometry offers advantages compared to other phase imaging methods :

• Robustness • Quantitative method • Works fine at energies suitable for mammography • Requires no temporal and little spatial coherence • Has potential to be scaled up to large fields of view


AcknowledgmentsAcknowledgments

At ESRF:

P. CloetensJ. Hoszowska E. Ziegler

and many others ...

Funding: Swiss National Science Foundation European Community

Many thanks to:

At PSIE. DeckardtF. GlausB. HaasY. HemmerlingL. HeydermanM. Lange J. Lehmann D. Meister T. Neiger B. Nöhammer T. Rohbeck


AcknowledgmentsAcknowledgments

At ESRF:

P. CloetensJ. Hoszowska E. Ziegler

and many others ...

Funding: Swiss National Science Foundation European Community

Many thanks to:

At PSIE. DeckardtF. GlausB. HaasY. HemmerlingL. HeydermanM. Lange J. Lehmann D. Meister T. Neiger B. Nöhammer T. Rohbeck

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