MRDust: Wireless Implant Data Uplink & Localization via Magnetic Resonance Image Modulation

TL;DR

This paper introduces MRDust, a novel implantable sensor system that actively modulates MRI signals for localized data transmission and precise implant localization, enhancing MRI's capabilities for physiological monitoring.

Contribution

The paper presents the design and validation of MRDust, a micrometer-scale implantable device that actively encodes data into MRI signals via magnetic resonance image modulation, enabling simultaneous communication and localization.

Findings

Successful voxel amplitude modulation demonstrated in MRI scans

Achieved a contrast-to-noise ratio of 25.58 in experiments

Power consumption of the device is 130 μW

Abstract

Magnetic resonance imaging (MRI) exhibits rich and clinically useful endogenous contrast mechanisms, which can differentiate soft tissues and are sensitive to flow, diffusion, magnetic susceptibility, blood oxygenation level, and more. However, MRI sensitivity is ultimately constrained by Nuclear Magnetic Resonance (NMR) physics, and its spatiotemporal resolution is limited by SNR and spatial encoding. On the other hand, miniaturized implantable sensors offer highly localized physiological information, yet communication and localization can be challenging when multiple implants are present. This paper introduces the MRDust, an active ``contrast agent" that integrates active sensor implants with MRI, enabling the direct encoding of highly localized physiological data into MR images to augment the anatomical images. MRDust employs a micrometer-scale on-chip coil to actively modulate the local magnetic field, enabling MR signal amplitude and phase modulation for digital data transmission. Since MRI inherently captures the anatomical tissue structure, this method has the potential to enable simultaneous data communication, localization, and image registration with multiple implants. This paper presents the underlying physical principles, design tradeoffs, and design methodology for this approach. To validate the concept, a 900 $\times$ 990 $\mu$m$^2$ chip was designed using TSMC 28 nm technology, with an on-chip coil measuring 630 $\mu$m in diameter. The chip was tested with custom hardware in an MR750W GE3T MRI scanner. Successful voxel amplitude modulation is demonstrated with Spin-Echo Echo-Planar-Imaging (SE-EPI) sequence, achieving a contrast-to-noise ratio (CNR) of 25.58 with a power consumption of 130 $\mu$W.