Minimally Invasive Imaging and Sensing Methods Based on Magnetic Particle Imaging and the Application of Implanted Electronic Circuits

Academic Background

In modern medicine, minimally invasive and biocompatible implantable bioelectronics are widely used for long-term monitoring of physiological processes inside the body. However, methods for imaging these devices and simultaneously extracting sensor information remain scarce and costly. Magnetic Particle Imaging (MPI) emerges as an ideal solution to this problem due to its zero background signal, high contrast, high sensitivity, and quantitative imaging capabilities. Unlike magnetic signals that can penetrate deeper tissues without being absorbed, MPI does not involve radiation dose, providing a safe and effective imaging pathway.

Paper Source

The paper, titled “Minimally Invasive Imaging and Sensing Methods Based on Magnetic Particle Imaging and the Application of Implanted Electronic Circuits,” was authored by Zhiwei Tay, Han-Joon Kim, John S. Ho, and Malini Olivo, among others. It was published in the IEEE Transactions on Medical Imaging journal in May 2024.

Summary of Research Content

a) Research Process

Subject and Device Modification
The research involves modifying common implantable devices by encapsulating superparamagnetic iron oxide nanoparticles (SPIOs) and magnetically coupling them to the device circuits, making them detectable through MPI. These modified implantable devices not only provide spatial information but also transmit sensor information from the magnetic nanoparticles by modulating harmonic signals.

Experimental Design and Testing Methods
The paper proposes an optimized MPI imaging technique by encapsulating and magnetically coupling SPIOs to the design circuits for imaging in MPI and using a handheld MPI reader to transmit sensor information. This information is transmitted via coded signals in the magnetic particle spectrum, such as through switching or frequency-shifting resistance/capacitance sensors to modulate harmonic signals.

Specific processes include:

1. Coupling and Extracting MPI Signals: Extracting sensor signals by modulating the excitation amplitude of SPIO nanoparticles through circuit sensors.
2. Establishing 3D Imaging Theory: Using handheld MPI readers to provide location and sensor reading information, reconstructing 3D positions through coordinates and sensor signals.

Algorithm and Data Analysis Methods
MPI signals are recorded and reconstructed using system matrix or x-space methods. Key algorithms include generating nonlinear magnetization response signals using Lissajous trajectories to perform 3D imaging within the field of view.

b) Main Results

1. Coupling and Signal Extraction: High-sensitivity sensor signals are obtained by modulating the amplitude of SPIO nanoparticles through the input magnetic field intensity delivered by circuit sensors.
2. 3D Imaging and Signal Position Reconstruction: The proposed angular correction strategy can also locate the 3D coordinates of implantable devices. Under certain experimental conditions, multi-layer tissues within a depth of 7 cm can still be imaged, providing accurate biosensor data.
3. Testing of Different Sensor Applications: Practical feasibility and accuracy of various sensors (e.g., temperature reading error of ±0.2°C, force reading error of 1-3%) were verified by combining NTC thermistors and thin-film pressure sensors.

c) Conclusion

This study demonstrates that MPI technology combined with implantable circuits can achieve the fusion of spatial information and sensor data imaging, opening up new application prospects for minimally invasive biomedicine and diagnostics. The results indicate that utilizing MPI’s zero background signal and efficient sensing mechanism has huge potential for diagnostic and therapeutic applications. Examples include monitoring mobile gastrointestinal sensors and post-operative deep surgical monitoring in clinical applications.

d) Research Highlights

• Important Findings: The study reveals how MPI combined with implantable electronic devices can achieve simultaneous acquisition of spatial information and sensor data.
• Innovative Methods: A new method was developed to encapsulate SPIOs into circuits and use handheld devices for imaging and data transmission.
• Broad Applications: The study shows the potential of MPI imaging for monitoring mobile implants or detecting environmental changes in deep tissues (e.g., inflammation, infection).

e) Other Important Information

Due to its non-radiative, safe, and efficient imaging characteristics, MPI is expected to expand its application range across fields in the future. However, the limitations of the current study also indicate the need to improve imaging depth and further optimize circuit design to reduce thermal effects of sensor currents. Future work will focus on these directions to achieve broader clinical applications.

Research Value

This study opens the door to non-invasive, remote, and precise monitoring of physiological parameters by combining modern information technology with medical imaging technology. This innovative approach holds significant potential application value in areas such as cancer treatment monitoring, post-operative rehabilitation, and chronic disease diagnosis. With further development and research, MPI-based technology is expected to become an important component of next-generation medical imaging and monitoring systems.