Considerations on the possibility of Phase Contrast Mammography using ICS sources B. Golosio a, P. Delogu b, I. Zanette b, M. Carpinelli a, G. L. Masala a, P. Oliva a, A. Stefanini b, S. Stumbo a 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

4 XRAYLIB: software libraries of x-ray fundamental parameters  compound materials refractive index real and imaginary part relatively 4 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. (see poster by P. Oliva et al.) 4 Phase Contrast imaging simulation software based on Geometrical Optics (see poster by I. Zanette et al.) 4 Phase Contrast imaging simulation software based on Fresnel-Kirchhoff integrals 4 Comparison among Phase Contrast imaging simulation methods and experimental measurements (also see poster by I. Zanette et al.) Simulation tools

4 Transverse coherence length: *small source linear size *large source-object distance 4 Longitudinal coherence length *small Energy Bandwidth 4 Phase contrast imaging using a polychromatic beam *first demonstrated by Wilkins et al. X-ray Phase Contrast imaging technique l t : coherence length z obj : source-object distance : wave length S: linear dimension of the source

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

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

4Challenging imaging task: *Normal and pathological tissues have very similar attenuation coefficients  Need to image small (100  m) details Low contrast High spatial resolution 4Fluence: compromise between image quality and delivered dose 4Best energy: depends on breast thickness and composition 4It has to match imaging detector efficiency. 4Accepted values for the best energy useful in mammography range: from 17keV to 25keV Mammography

4In mammography X-rays are used to produce images of the human breast. 4Traditional radiation sources used in mammography are X-ray tubes. Typical Fluence: 10 7  /mm 2 65 cm X-ray tubes in Mammography

4Photon fluence and rate  Large photon fluence (~10 7  /mm 2 ) *Large image size (18x24cm 2 ) *Short time duration (a few seconds maximum) äPatient movements can affect image quality äuncomfortable exam (breast is compressed) äPulse duration in conventional mammography: ms Flux requirements for mammography We need a flux of  /s

Object 4 Approximations *fully described by refractive index *neglect scattering from interatomic structure *straight-line propagation within the sample: thin sample 4 Transmission function

Propagation in free space 4 Huygens-Fresnel principle, Kirchhoff integral

4 Tumor like mass *Spherical shape *1 mm diameter *glandular tissue composition *density g/cm 3 4 Breast tissue *4 cm thickness *50 % glandular tissue *50 % adipose tissue *density g/cm 3 4 Compositions from ICRU 44 4 Dose: 1.5 mGy 4 Fluence: 2.09·10 7 photons/mm 2 at 20 keV monochromatic energy Simulated Reference Sample and parameters for mammography

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

Effect of source size and detector PSF

C abs C Ph C Ph : Phase Contrast C abs : Absorption Contrast Edge Enhancement Index (EEI)

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

Absorption image Pure phase image

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

Same image without noise

Contrast detail phantom 4Rows: same thickness 4Columns: same diameter 4Visibility depends on: *Contrast *Noise *Area

Detail visibility (absorption image) half minimum

Visibility (phase contrast image) half maximum

4E = 20 keV   E = 0 4z 1 = 5 m 4z 2 = 10 m 4M = 2  Detector FWHM = 120  m  Source linear size S = 13  m 4Detail diameter d = 1 mm 4Slab thickness l = 4 cm Source Sample Detector x I z1z1 z2z2 Basic parameters

Source Sample Detector x I z1z1 z2z2 4z 1 = 8 m, z 2 = 10 m 4M = Little magnification Magnification M=1.25, z 1 = 8 m

4z 1 = 2 m, z 2 = 10 m 4M = 5 4Significant magnification Source Sample Detector x I z1z1 z2z2 Magnification M=5, z 1 = 8 m

4z 1 = 2 m, z 2 = 10 m 4M = 5 4Significant magnification 4z 1 = 8 m, z 2 = 10 m 4M = Little magnification Intensity after convolution with detector and source PSF

Source PSF width Source linear size S = 13 mm Source PSF width: FWHM src = S  z 12 / z 1 4z 1 = 8 m, z 12 = 2 m 4FWHM src = 3.25 mm 4Not significant compared to detector PSF 4z 1 = 2 m, z 12 = 8 m 4FWHM src = 52 mm 4Significant compared to detector PSF Source point object point image z 12 z1z1 Source point object point image z1z1 z 12

Visibility versus energy Optimal energy around 19 keV

Visibility versus energy bandwidth

Visibility versus source-object distance (m)

Visibility versus detector PSF FWHM

Visibility versus detail diameter

4 ICS sources may be suitable for Phase Contrast Mammography 4 Energy bandwidth does not significantly affect performance HOWEVER 4Flux should be higher by at least 1 order of magnitude  High resolution (<50  m), large area detectors needed 4Advantage of Phase Contrast over Absorption Radiography seems to be limited to tumors having ~1 mm or lower size Conclusions