Compact x-ray sources for mammographic applications: Monte Carlo simulations of image quality P. Oliva, a B. Golosio, and S. Stumbo Struttura Dipartimentale di Matematica e Fisica dell’Università degli Studi di Sassari and Sezione INFN, Cagliari 07100, Italy A. Bravin European Synchrotron Radiation Facility, 38043 Grenoble, France P. Tomassini INFN, Section of Milano, 20133 Milan, Italy Received 3 August 2007; revised 2 September 2009; accepted for publication 21 September 2009; published 9 October 2009 Thomson scattering x-ray sources can provide spectral distributions that are ideally suited for mammography with sufficient fluence rates. In this article, the authors investigate the effects of different spectral distributions on the image quality in simulated images of a breast mammographic phantom containing details of different compositions and thicknesses. They simulated monochro- matic, quasimonochromatic, and polychromatic x-ray sources in order to define the energy for maximum figure of merit signal-difference-to-noise ratio squared/mean glandular dose, the effect of an energy spread, and the effect of the presence of higher-order harmonics. The advantages of these sources with respect to conventional polychromatic sources as a function of phantom and detail thickness were also investigated. The results show that the energy for the figure of merit peak is between 16 and 27.4 keV, depending on the phantom thickness and detail composition and thickness. An energy spread of about 1 keV standard deviation, easily achievable with compact x-ray sources, does not appreciably affect the image quality. © 2009 American Association of Physicists in Medicine. DOI: 10.1118/1.3245876 Key words: Thomson scattering, mammography, x-ray spectra, quasimonochromatic spectra I. INTRODUCTION Mammography is a challenging field of medical imaging. The small difference in absorption coefficients between nor- mal and cancerous breast tissues leads to low contrast on some details of diagnostic interest like thin tumor masses. The possibility of tuning the x-ray energy as a function of the breast composition and thickness is essential in order to re- duce the dose to the patient and optimize the image quality. Broad spectra like those produced by x-ray tubes are gener- ally less effective than a monochromatic source of the appro- priate energy. Photons of energies other than the one maxi- mizing a signal-difference-to-noise ratio squared/mean glandular dose MGD figure of merit lead to lower contrast in the case of higher energies or higher dose to the patient in the case of energies lower than the optimal one. The traditional x-ray sources used in mammography are x-ray tubes. The photon spectrum is tuned by an appropriate choice of anode material, K-edge filtration, and peak kilo- voltage. However, the energy spectrum of conventional mammographic x-ray tube systems is polychromatic, and even after K-edge filtration, it shows an appreciable number of photons in the whole range between about 10 keV and the maximum photon energy. 1 Synchrotron radiation SR sources can provide highly monochromatic, energy-tunable radiation. Different imaging techniques based on the properties of SR have been applied to the medical field, e.g., conventional full-field imaging with monochromatic radiation, phase contrast imaging, and analyzer-based imaging. 2–6 The advantages of such tech- niques with respect to clinical mammography have been widely proven in literature. However, due to high costs, lim- ited beam time, and practical problems, synchrotrons cannot replace conventional x-ray tube systems in routine mammo- graphic examinations. An x-ray diffraction-based system for mammography 7 or breast CT Ref. 8 has been proposed by Gambaccini et al. Quasimonochromatic beams are obtained via mosaic crystal Bragg diffraction with an x-ray tube. The mean energy and energy spread of the spectrum are tunable, but the fluence at the detector 67 cm from the focal spot is lower than 10 5 photons mm -2 mA s -1 . 9 Another approach for the generation of quasimonochro- matic beams is K-edge filtering. 10 In this technique, the spec- tra are shaped by controlling the filter material/thickness and tube potential in order to optimize image quality for different breast/detail thicknesses or compositions. Improvements in the image quality are obtained for filtrations that reduce the fluence by factors of 100–500, so the final fluence is compa- rable to the one obtained by diffraction-based methods. A new generation of quasimonochromatic, high flux x-ray sources is under development. They are based on Compton or Thomson scattering TS of photons produced by a laser on a highly focused electron beam. 11–13 These sources can potentially be much more compact, less expensive than syn- 5149 5149 Med. Phys. 36 „11…, November 2009 0094-2405/2009/36„11…/5149/13/$25.00 © 2009 Am. Assoc. Phys. Med.