Emilie Franceschini | PubMed Health

PubMed2006

A 2-D anatomic breast ductal computer phantom for ultrasonic imaging.

Most breast cancers (85%) originate from the epithelium and develop first in the ductolobular structures. In screening procedures, the mammary epithelium should therefore be investigated first by the performing of an anatomically guided examination. For this purpose (mass screening, surgical guidance), we developed a two-dimensional anatomic phantom corresponding to an axial cross section of the ductolobular structures, which makes it possible to better understand the interactions between the breast composition and ultrasound. The various constitutive tissues were modeled as a random inhomogeneous continuum with density and sound speed fluctuations. Ultrasonic pulse propagation through the breast computer phantom was simulated using a finite element time domain method (the phantom can be used with other propagation codes). The simulated ductal echographic image is compared with the ductal tomographic (DT) reconstruction. The preliminary results obtained show that the DT method is more satisfactory in terms of both the contrast and the resolution.

Algorithms↗

PubMed2005

Soft tissue absorption tomography with correction for scattering aberrations.

Among the many factors involved in ultrasound attenuation phenomena, scattering effects play a major role, even in the unexpected case of soft tissues. It is proposed in this study to quantitatively evaluate the scattering affecting the measurements before reconstructing the absorption parameter alone. The reconstruction procedure involves three steps: (1) Estimating the sound speed map using a transmission tomography algorithm. This estimation procedure provides a numerical phantom of the organ probed, cleared of all dissipative components. This absorption free phantom mimics the (viscoacoustic) tissues imaged except for the density and absorption characteristics: the density a priori equals 1000 kg/m3 and the absorption is not taken into account. The impedance fluctuations in the object are therefore approximated on the basis of the sound speed contrast. (2) Synthesing the field scattered by the absorption free phantom; the attenuation observed here results solely from the scattering phenomenon. The synthesis is carried out using a finite-element time domain code simulating the ultrasonic propagation through the phantom. It provides the scattering distortion reference introduced into the log spectral absorption estimator. (3) Reducing the scattering distortions affecting the integrated absorption measured along the ray paths using a log spectral procedure. The corrected integrated absorption is then processed using a tomographic reconstruction procedure that provides an estimate of the absorption distribution. Simple numerical simulations show the improvement obtained in the absorption estimates with this approach.

Absorption↗