Euromedim 2006 :1st European Conference on Molecular Imaging Technology

Ultrasound Mammography

10 May 2006, 15:00

15m

Palais du Pharo, Marseille

oral S3_S4 others modalities Other Modalities

Speaker

Dr Serge Mensah (CNRS - LMA)

Description

Breast cancer is the first cause of mortality of women aged 55 to 75. It is only in the last decade that breast anatomy has started being seriously considered by pioneer radiologists such as M. Stravos, M. Teboul and D. Amy. Indeed, it is now widely admitted that 90% cancer lesions and mainly all the specific diseases of the breast initiate from the epithelium and develop first in the ductolobular structures (infiltration of Cooper's ligaments). Thus, the restitution of breast anatomy appears of prime importance since the examination of the gland should be guided by a relevant exploration strategy. We introduce a near-field formulation of the acoustic field scattered by a soft tissue organ such as the breast (assumed to be weakly heterogeneous). This derivation is based on the Huygens-Fresnel principle that describes the scattered field as the result of the interferential scheme of all the secondary spherical waves. This derivation leads us to define a new Fourier transform which yields a spectrum whose harmonic components have an elliptical spatial support. Based on these projections, we define the Elliptical Radon transform and show that it is possible to reconstruct either the impedance or the celerity maps of an acoustical model characterized in terms of impedance and celerity fluctuations. We observe that this formulation is very similar to that developed in the far field domain where the Radon transform pair is derived from an harmonic plane wave decomposition. This formulation allows us to introduce the Ductal Tomography, following the example of the Ductal Echography, that provides a systematic inspection of each mammary lobe, in order to reveal lesions at an early stage. In order to review the performances obtained with current echographs in view of specific experiment (numerical simulations), we develop a computer phantom that gains in realism. This 2-D anatomical phantom is an axial cut of the ductolobular structure corresponding to a daisy-like internal arrangement with petals (lobes) radiating around the nipple, for healthy and pathological situations. The different constitutive tissues and ducts are characterized in terms of density and celerity parameters whose spatial distributions are defined with specific random density laws. The use of a velocity-pressure formulation permits us to model time domain acoustic wave propagation. Broadband US pulses are transmitted and measured in diffraction around the breast with a ring antenna, the images are reconstructed using the elliptical back-projection-based procedure mentioned above. The results show that a tomographic approach provides much more information both about the breast structure (navigation) and about the lesion (specificity) than conventional echography. We conclude by introducing the mammograph prototype in development in our laboratory and some perspectives in molecular ultrasounds based on contrast agent microbubbles. Keywords : ultrasound mammography, near-field, anatomic breast phantom, prototype.