Biqi Rebekah Zhao

EECS Department, University of California, Berkeley

Technical Report No. UCB/

May 1, 2025

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 signal-to-noise ratio (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. In this dissertation, I introduce MRDust, an active “contrast agent” that integrates miniaturized implantable sensors with MRI, enabling the direct encoding of highly localized physiological data into MR images to augment the anatomical images. The MRDust implant combines ultrasonic energy harvesting, physiological sensing, and a micrometer-scale on-chip coil that actively modulates the local magnetic field to transmit digital data via MR signal amplitude and phase modulation. Leveraging MRI’s inherent anatomical mapping, this approach enables simultaneous data communication, localization, and image registration across multiple implants. To realize this vision, I first present the physical principles of MR image modulation with a micro-coil and analyze design trade-offs between coil geometry, coil current, and MR pulse sequence parameters. These insights guided the development of three proof-of-concept systems: The first prototype is an off-the-shelf system used to validate the MR image modulation concept, demonstrating operation in a GE 3T scanner synchronized with gradient-echo echo-planar imaging (GRE-EPI) and spin-echo echo-planar imaging (SE-EPI) sequences. The second, MRDust I, implements an on-chip micro-coil for active MR image modulation, and its operation in the scanner confirms the feasibility of using a chip-scale coil for MR image modulation. The third, MRDust II, is a fully wireless miniature pressure sensor integrating ultrasonic energy harvesting, piezoresistive pressure sensing with analog frontend (AFE) readout, and MR-based data communication and localization. Together, these prototypes demonstrate successful MR image modulation, as well as preliminary results in wireless energy harvesting, pressure sensing, and data uplink. The dissertation concludes by discussing potential future directions and applications.

Advisors: Michael Lustig and Rikky Muller

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BibTeX citation:

@phdthesis{Zhao:31911,
    Author= {Zhao, Biqi Rebekah},
    Title= {Miniature Wireless Sensor Implant with Data Communication and Localization via Magnetic Resonance Imaging},
    School= {EECS Department, University of California, Berkeley},
    Year= {2025},
    Number= {UCB/},
    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 signal-to-noise ratio (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.
In this dissertation, I introduce MRDust, an active “contrast agent” that integrates miniaturized implantable sensors with MRI, enabling the direct encoding of highly localized physiological data into MR images to augment the anatomical images. The MRDust implant combines ultrasonic energy harvesting, physiological sensing, and a micrometer-scale on-chip coil that actively modulates the local magnetic field to transmit digital data via MR signal amplitude and phase modulation. Leveraging MRI’s inherent anatomical mapping, this approach enables simultaneous data communication, localization, and image registration across multiple implants.
To realize this vision, I first present the physical principles of MR image modulation with a micro-coil and analyze design trade-offs between coil geometry, coil current, and MR pulse sequence parameters. These insights guided the development of three proof-of-concept systems: The first prototype is an off-the-shelf system used to validate the MR image modulation concept, demonstrating operation in a GE 3T scanner synchronized with gradient-echo echo-planar imaging (GRE-EPI) and spin-echo echo-planar imaging (SE-EPI) sequences. The second, MRDust I, implements an on-chip micro-coil for active MR image modulation, and its operation in the scanner confirms the feasibility of using a chip-scale coil for MR image modulation. The third, MRDust II, is a fully wireless miniature pressure sensor integrating ultrasonic energy harvesting, piezoresistive pressure sensing with analog frontend (AFE) readout, and MR-based data communication and localization. Together, these prototypes demonstrate successful MR image modulation, as well as preliminary results in wireless energy harvesting, pressure sensing, and data uplink. The dissertation concludes by discussing potential future directions and applications.},
}

EndNote citation:

%0 Thesis
%A Zhao, Biqi Rebekah 
%T Miniature Wireless Sensor Implant with Data Communication and Localization via Magnetic Resonance Imaging
%I EECS Department, University of California, Berkeley
%D 2025
%8 May 1
%@ UCB/
%F Zhao:31911