1. Département de Physique; Université de Montréal; Pavillon Roger-Gaudry, 2900 Boulevard Édouard-Montpetit Montréal Québec H3T 1J4 Canada
2. National Physical Laboratory; Acoustics and Ionising Radiation Team; Hampton Road Teddington TW11 0LW United Kingdom
3. Department of Medical Physics and Biomedical Engineering; University College London; Gower Street London WC1E 6BT United Kingdom
4. Centre de recherche du Centre hospitalier de l'Université de Montréal; Montréal QC H2X 0A9 Canada