Current density imaging of electrical current pathways inside the pig torso

Low frequency current density imaging (LFCDI) using a magnetic resonance (MR) imager has been shown to accurately measure electrical current density inside a phantom. CDI measures the magnetic field generated by the current and converts it to current density (CD) by computing its curl. Therefore, CDI avoids both the inverse problem and invasiveness of other electrical measurement techniques such as electrical impedance tomography and direct electrode measurement. This makes CDI an ideal technique for studying the current flow inside the body during electrical therapies such as defibrillation where the current density in tissue is closely associated with the efficacy. Here we report simultaneous measurements of current density at all points within the pig torso during an electrical current application through defibrillation electrodes. Current flow was visualized by computing streamlines from the current density vectors. We observed current flow over the chest walls in agreement with the current literature. However, complex and unexpected current flow patterns were seen inside the heart as well as in the surrounding vasculature. This study represents the first noninvasive volume current measurement inside the pig torso during an electrical current application.