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Deformation of the energy spectrum from a $^{99m}$Tc source with its depth

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  • Biology
  • Medicine
  • Physics

Abstract

DEFORMATION OF THE ENERGY SPECTRUM FROM A 99MTC SOURCE WITH ITS DEPTH DEFORMATION OF THE ENERGY SPECTRUM FROM A 99MTC SOURCE WITH ITS DEPTH V. Breton, D. Lazaro, L. Méritet, J. Berthot, G. Montarou LPC, Clermont-Ferrand, France J. Maublant, C. Thouly CJP, Clermont-Ferrand, France Abstract Planar scintimammography with 99mTc-Sestamibi is a sensitive, specific and non invasive method used in complement to X-ray mammography for breast cancer diagnosis. Studies [1] have shown how scatter correction might improve lesion detection and quantitation of tumor-to-normal breast tissue activity ratio. Among the strategies used to compute this correction, some are based on the analysis of the energy spectrum of photons [2]. In a similar approach, this paper presents experimental and Monte-Carlo results on the deformation of the energy spectrum in correlation with the depth of the source. It focuses on the exploitation of the deformation of the energy spectrum to compute the depth of a tumor. 1 MOTIVATION Planar scintimammography has not yet been proven to be overthrown by SPECT. Its specifity of about 87- 89 % and sensitivity of about 92 % [3] decreases to 50 % when considering small lesions. An approach to improve the detection of small lesions is to try to better exploit ALL the information collected in planar scintigraphy. Indeed, the part of the energy spectrum used for image reconstruction is the one defined by the acquisition energy window. Typically centred on the emission energy of the isotope, its width defined as a percentage of this energy, usually 20% (e.g. 126-154 keV for 99mTc), can be shrunk to reduce scatter contamination. Several groups are now working on studying the effects of Compton scattering on image contrast and lesion detection [4,5,6,7]. Many scatter correction techniques have been studied and developed during last years [8,9,10]. Among the different strategies successfully applied to compute scatter corrections, the so-

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