ÉCHOGRAPHIE OCULAIRE TRANSCORNÉENNE PAR SONDE LINÉAIRE MULTI-ÉLÉMENTS HAUTE-FRÉQUENCE : Étude et correction des effets aberrateurs du cristallin dans la reconstruction d'image en mode-B

摘要

In ophthalmic ultrasonography the crystalline lens is known to be the main source of phase aberration, as ultrasounds (US) propagate about 10% faster than in the surrounding intra-ocular medium. Hence, it impairs significantly both spatial and contrast resolution of axial B-scans, and in addition causes important distortion, especially on the ocular fundus.To deal with this issue and in view of the next coming of US arrays in ophthalmologic practice, we developed in this thesis an adapted beamforming (BF) free from crystalline lens aberration. It lies on a two point ray tracing approach to compute focusing delays that take into account crystalline lens aberrations including refraction at the interface. Initially developed considering a uniform US velocity in the lens, the adapted BF has been extended to consider the velocity gradient that exists in the real lens.In vitro and ex vivo results obtained with a 20 MHz linear array driven by a US research scanner (the ECODERM) are reported.