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Considerations on the possibility of Phase Contrast Mammography using ICS sources

This study explores the feasibility of using inverse Compton scattering (ICS) sources for phase contrast mammography, discussing the simulation tools, imaging technique, and parameters needed. The simulation results show promising potential for ICS sources in phase contrast mammography.

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Considerations on the possibility of Phase Contrast Mammography using ICS sources

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  1. Considerations on the possibility of Phase Contrast Mammography using ICS sources B. Golosioa, P. Delogub, I. Zanetteb, M. Carpinellia, G. L. Masalaa, P. Olivaa, A. Stefaninib, S. Stumboa a. Strutt. Dip. di Matematica e Fisica, Università di Sassari and INFN Sez. di Cagliari b. Dipartimento di Fisica, Università di Pisa and INFN Sez. di Pisa Compton Sources for X/g rays - Alghero 7-12 September 2008

  2. Simulation tools • XRAYLIB: software libraries of x-ray fundamental parameters  compound materials refractive index real and imaginary part relatively • Specialized Monte Carlo simulation software based on variance reduction techniques, much faster than other general purpose Monte Carlo Codes  detailed study of absorption imaging using monochromatic, polychromatic and quasi-monochromatic sources, role of scattering background, etc. (seeposter by P. Oliva et al.) • Phase Contrast imaging simulation software based on Geometrical Optics (seeposter by I. Zanette et al.) • Phase Contrast imaging simulation software based on Fresnel-Kirchhoff integrals • Comparison among Phase Contrast imaging simulation methods and experimental measurements (also seeposter by I. Zanette et al.)

  3. X-ray Phase Contrast imaging technique • Transverse coherence length: • small source linear size • large source-object distance • Longitudinal coherence length • small Energy Bandwidth • Phase contrast imaging using a polychromatic beam • first demonstrated by Wilkins et al. lt: coherence length zobj: source-object distance l: wave length S: linear dimension of the source

  4. Some typical ICS source parameters • Small source size: FWHM  10-20 mm • Small angular divergence: q 5 mrad  relatively high intensity at large distance from the source • Quasi-monochromatic spectrum: • energy bandwidth relatively small compared to x-ray tube systems  ICS sources are suitable for Phase Contrast imaging Are they suitable for Phase Contrast mammography?

  5. MAMMOGRAPHY - MASSIVE TUMORS SPICULATED LESION ON FIBROADIPOSE TEXTURE SPICULATED LESIONS ON FIBROGLANDULAR TEXTURE MICROCALCIFICATIONS TALK BY A. CEDOLA

  6. Mammography • Challenging imaging task: • Normal and pathological tissues have very similar attenuation coefficients • Need to image small (100m) details Low contrast High spatial resolution • Fluence: compromise between image quality and delivered dose • Best energy: depends on breast thickness and composition • It has to match imaging detector efficiency. • Accepted values for the best energy useful in mammography range: from 17keV to 25keV

  7. 65 cm X-ray tubes in Mammography • In mammography X-rays are used to produce images of the human breast. • Traditional radiation sources used in mammography are X-ray tubes. Typical Fluence: 107/mm2

  8. We need a flux of 1011 - 1012 g/s Flux requirements for mammography • Photon fluence and rate • Large photon fluence (~107g/mm2) • Large image size (18x24cm2) • Short time duration (a few seconds maximum) • Patient movements can affect image quality • uncomfortable exam (breast is compressed) • Pulse duration in conventional mammography: 200-500 ms

  9. Object • Approximations • fully described by refractive index • neglect scattering from interatomic structure • straight-line propagation within the sample: thin sample • Transmission function

  10. Propagation in free space • Huygens-Fresnel principle, Kirchhoff integral

  11. Simulated Reference Sample and parameters for mammography • Tumor like mass • Spherical shape • 1 mm diameter • glandular tissue composition • density 1.044 g/cm3 • Breast tissue • 4 cm thickness • 50 % glandular tissue • 50 % adipose tissue • density 0.984 g/cm3 • Compositions from ICRU 44 • Dose: 1.5 mGy • Fluence: 2.09·107 photons/mm2 at 20 keV monochromatic energy

  12. Simulated image of a tumor-like object (d=1mm) in breast tissue Absorption image Phase Contrast image

  13. Effect of source size and detector PSF

  14. Edge Enhancement Index (EEI) CPh : Phase Contrast Cabs : Absorption Contrast CPh Cabs

  15. Simulated PhC image of tumor-like object in breast tissue • Detail diameter: 3 mm, slab thickness 4 cm • monochromatic energy 1 keV • detector PSF FWHM 100 mm, source size FWHM 13 mm • source-object distance 5 m, object detector distance 5 m • Edge enhancement index: EEI>1

  16. Absorption image Pure phase image

  17. Where is the dark circle? Noisy image Where is the bright ring? Remove noise

  18. Same image without noise

  19. Contrast detail phantom • Rows: same thickness • Columns: same diameter • Visibility depends on: • Contrast • Noise • Area

  20. Detail visibility (absorption image) half minimum

  21. Visibility (phase contrast image) half maximum

  22. Basic parameters I • E = 20 keV • DE = 0 • z1 = 5 m • z2 = 10 m • M = 2 • Detector FWHM = 120 mm • Source linear size S = 13 mm • Detail diameter d = 1 mm • Slab thickness l = 4 cm Detector x Sample z2 z1 Source

  23. Magnification M=1.25, z1 = 8 m I • z1 = 8 m, z2 = 10 m • M = 1.25 • Little magnification Detector x Sample z2 z1 Source

  24. Magnification M=5, z1 = 8 m I • z1 = 2 m, z2 = 10 m • M = 5 • Significant magnification Detector x z2 Sample z1 Source

  25. Intensity after convolution with detector and source PSF • z1 = 8 m, z2 = 10 m • M = 1.25 • Little magnification • z1 = 2 m, z2 = 10 m • M = 5 • Significant magnification

  26. Source PSF width • Source linear size S = 13 mm • Source PSF width: FWHMsrc = S  z12 / z1 • z1 = 8 m, z12 = 2 m • FWHMsrc = 3.25 mm • Not significant compared to detector PSF • z1 = 2 m, z12 = 8 m • FWHMsrc = 52 mm • Significant compared to detector PSF point image point image z12 point object z12 z1 point object z1 Source Source

  27. Visibility versus energy Optimal energy around 19 keV

  28. Visibility versus energy bandwidth

  29. Visibility versus source-object distance (m)

  30. Visibility versus detector PSF FWHM

  31. Visibility versus detail diameter

  32. Conclusions • ICS sources may be suitable for Phase Contrast Mammography • Energy bandwidth does not significantly affect performance HOWEVER • Flux should be higher by at least 1 order of magnitude • High resolution (<50 mm), large area detectors needed • Advantage of Phase Contrast over Absorption Radiography seems to be limited to tumors having ~1 mm or lower size

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