Magnetic Manipulation of Blood Conductivity with Superparamagnetic Iron Oxide-Labeled Erythrocytes

The active and passive electrophysiological properties of blood and tissue have been utilized in a vast array of clinical techniques to noninvasively characterize anatomy and physiology, and to diagnose a wide variety of pathologies. However, the accuracy and spatial resolution of such techniques is limited by several factors, including an ill-posed inverse problem, which determines biological parameters and signal sources from surface potentials. Here, we propose a method to noninvasively modulate tissue conductivity by aligning superparamagnetic iron oxide (SPIO) labeled erythrocytes with an oscillating magnetic field. A prototype device is presented, which incorporates a three-dimensional set of Helmholtz coil pairs and fluid channel embedded electrode arrays. Alignment of labeled cells (~11 mM iron) within a 12 mT field is demonstrated, and this directed reorientation is shown to alter the conductivity of blood by ~5% and ~0.5% for stationary and flowing blood, respectively, within fields as weak as 6-12 mT. Focal modulation of conductivity could drastically improve numerous bioimpedance-based detection modalities.