A tomographic method based on the Lorentz force for the measurement of the pressure of an ultrasound transducer is presented. When a metal wire is vibrating under the influence of a pressure field created by an ultrasound transducer while submitted to a magnetic field, the Lorentz force induces an electrical current. This current is considered proportional to the integral of pressure along the wire. By moving the wire perpendicular to the ultrasound axis, and rotating it around the same axis, a sinogram of the pressure field can be elaborated. Then an inverse Radon transform of the signal gives the pressure field spatial distribution. An experiment was conducted where a 1 MHz transducer generated an ultrasound wave with a focal point at 4 cm. A 100 μm in diameter shielded copper wire was placed perpendicular to the ultrasound propagation axis, and inside a 300 mT magnetic field created by a permanent magnet. The main advantages of the hydrophone created by the wire-magnet system are the large frequency bandwidth and the resistance to high pressure, parameters still under investigation. Possible disadvantages are the sensibility to electromagnetic noise and the possible distortion of the pressure field when using a too thick wire.