3D rendering of a microbot.Getty Images
Researchers from Huazhong University of Science and Technology in China have developed a new magnetic resonance imaging (MRI) technique that enables real-time, artifact-free navigation of magnetic microrobots inside the body.
The approach significantly improves imaging speed and tracking accuracy, addressing a long-standing challenge in MRI-driven robotic control.
Magnetic microrobots are considered a promising tool for minimally invasive medical procedures, including targeted drug delivery, precision therapies, and theranostic interventions.
Their small size and magnetic responsiveness allow them to move through complex biological environments that are difficult to access using conventional tools.
MRI offers deep tissue penetration and high spatial resolution, making it an ideal platform for guiding such robots.
However, traditional MRI sequences are slow, with repetition times of around 1,000 milliseconds, creating delays that limit real-time control and introduce imaging artifacts.
These limitations reduce tracking accuracy and interfere with the magnetic gradients used to drive the robots, making precise navigation difficult during live procedures.
Seeing robots live inside
To overcome these challenges, the researchers developed a multi-frequency dual-echo (MFDE) MRI sequence that reduces repetition time to just 30 milliseconds. This enables near real-time imaging while maintaining high spatial accuracy.
The MFDE sequence uses two adjacent 180-degree radio-frequency pulses to generate dual echoes, accelerating proton spin recovery.
To counter signal loss caused by steady-state effects at such short repetition times, the team alternated positive and negative offset frequency excitations, preserving image quality.
Using this approach, the system achieved magnetic particle positioning with a relative error of less than 1percent.
The duty cycle of the driving gradient reached 77 percent, eliminating interference between imaging gradients and robot motion and producing artifact-free background images.
The researchers also developed a reconstruction algorithm that replaces artifacts with bright spots on a pre-obtained background image, allowing continuous visualization of the robot’s position during motion.
From mazes to biology
The system was validated through a series of experiments, beginning with maze navigation
A magnetic robot was guided through a complex three-dimensional maze, with its position updated in real time on a three-view imaging platform. The robot was controlled using a joystick, enabling precise manual adjustments.
In phantom endovascular models, the robot successfully navigated through tortuous vessel-like structures, demonstrating the technique’s potential for minimally invasive vascular interventions.
The researchers further tested the approach in vivo in the large intestine of a rat.
The magnetic robot navigated the biological environment under real-time MRI guidance, highlighting the system’s potential as an alternative to traditional colonoscopy procedures.
By resolving the trade-off between imaging speed and quality, the MFDE MRI sequence represents a major step forward in MRI-driven robotic navigation.
The technology could improve precision and safety in future minimally invasive medical procedures.
The study was published in the journal Engineering.
