  The ability of the Lorentz force to link a mechanical displacement to an
electrical current presents a strong interest for medical acoustics, and three
applications were studied in this thesis. In the first part of this work, a
hydrophone was developed for mapping the particle velocity of an acoustic
field. This hydrophone was constructed using a thin copper wire and an external
magnetic field. A model was elaborated to determine the relationship between
the acoustic pressure and the measured electrical current, which is induced by
Lorentz force when the wire vibrates in the acoustic field of an ultrasound
transducer. The built prototype was characterized and its spatial resolution,
frequency response, sensitivity, robustness and directivity response were
investigated. An imaging method called Lorentz Force Electrical Impedance
Tomography was also studied. In this method, a biological tissue is vibrated by
ultrasound in a magnetic field, which induces an electrical current by Lorentz
force. The electrical impedance of the tissue can be deduced from the
measurement of the current. This technique was applied for imaging a gelatin
phantom, a beef muscle sample, and a thermal lesion in a chicken breast sample.
This showed the method may be useful for providing additional contrast to
conventional ultrasound imaging. Finally, this thesis demonstrated that shear
waves can be generated in soft tissues using Lorentz force. This work was
performed by applying an electrical current with two electrodes in a soft solid
placed in a magnetic field. Shear waves were observed in gelatin phantom and
liver sample. The speed of the shear waves were used to compute elasticity and
their source to map the electrical conductivity of the samples.
