Thermal lesion imaging using Lorentz force: Proofs of concept

Abstract

The Lorentz force can be used by different means to image thermal lesions in biological tissue. In the first method presented here, so-called magneto-acoustical electrical tomography, a tissue sample is held in a magnetic field and is subsequently exposed to a focused ultrasound beam. The displacement within the magnetic field caused by this ultrasound beam results in an electrical current due to the Lorentz force. In this way, the change in electrical conductivity due to the presence of thermal lesions can then be observed. Conversely, when an electrical current is applied to tissue placed in a magnetic field, a shear wave is induced by the Lorentz force. Elastography images can be reconstructed from this shear wave, revealing thermal lesions by the change in elastic modulus. The first method was tested on ex-vivo chicken breast sample with a 500 kHz transducer and a 300 mT magnetic field. The second method was tested on gelatin phantom with a 100 mA current and 300 mT magnetic field. Images and results will be presented for both methods. These techniques could be used for the monitoring of thermal lesion formation in high intensity focused ultrasound treatment.