Canadian researchers led by Montreal radiologist Gilles Soules have developed a new method for treating liver tumors using a magnet-guided microrobot in an MRI device.

The idea of ​​inserting microscopic robots into the bloodstream to heal the human body is not new. It’s not even science fiction.

Guided by an external magnetic field, tiny biocompatible robots, made of magnetic iron oxide nanoparticles, could theoretically deliver medical treatments in a highly targeted manner.

Until now, there has been one technical hurdle: the gravitational force of these microrobots is greater than the magnetic force, which limits their guidance when the tumor is elevated above the injection site.

While the magnetic field of MRI is high, the magnetic gradient used for navigation and creating MRI images is weak.

“To solve this problem, we developed an algorithm that determines the position that the patient’s body should be in for clinical MRI to take advantage of gravity and combine it with the magnetic navigation force, ” said Dr. Gilles Soules, one of its researchers. Director of the Department of Radiology, Radio-Oncology and Nuclear Medicine at the CHUM Research Center and Université de Montréal.

“This combined effect makes it easier for the microrobots to travel to the arterial branches that feed the tumor,” he said. “By varying the direction of the magnetic field, we can precisely guide it to the areas to be treated and thus preserve healthy cells.”

Towards greater accuracy

Published in Science Roboticsthis proof of concept could change the way interventional radiology is used to treat liver cancer.

The most common of these, hepatocellular carcinoma, is responsible for 700,000 deaths worldwide each year, and is currently most often treated with transarterial chemoembolization.

Requiring highly skilled personnel, this invasive treatment involves administering chemotherapy directly into the artery feeding the liver tumor and cutting off the tumor’s blood supply using X-ray-guided microcatheters.

“Our magnetic resonance navigation approach can be performed using an implantable catheter similar to that used in chemotherapy,” Soules said. “Another advantage is that tumors are better visualized on MRI than on X-ray.”

For this study, Soulez and his research team collaborated with Sylvain Martel (Polytechnique Montréal) and Urs O’Hefeli (University of British Columbia). The study’s first author, Ning Li, is a postdoctoral fellow in Dr. Soulez’s laboratory.

Thanks to the development of an MRI-compatible microrobot injector, scientists were able to assemble “particle trains” of magnetizable microrobots. Because they have a high magnetic force, they are easy to pilot and detect on images provided by an MRI device.

In this way, scientists can ensure not only that the train is moving in the right direction, but also that the treatment dose is sufficient. Over time, each microrobot will carry a portion of the treatment, so it’s important that radiologists know how many.

A good sense of direction

“We conducted trials on twelve pigs to mimic the patient’s physiological conditions as closely as possible,” Soliz said. “This proved fruitful: the microrobots preferentially navigated the branches of the hepatic artery targeted by the algorithm and reached their destination.”

His team ensured that the location of the tumor in different parts of the liver did not affect the effectiveness of such an approach.

“Using an anatomical atlas of human livers, we were able to simulate the piloting of microrobots on 19 patients treated with transarterial chemoembolization,” he said. “They had a total of thirty tumors at different locations in their livers. In more than 95 percent of cases, the tumor location was consistent with the navigation algorithm to reach the targeted tumor.”

Despite this scientific progress, clinical application of this technology is still a long way off.

“First, using artificial intelligence, we need to improve the real-time navigation of the microrobots by detecting their location in the liver and occlusions in the branches of the hepatic artery feeding the tumor,” Soules said. Presence also needs to be detected.”

Scientists will also need to model blood flow, patient positioning and magnetic field direction using software that simulates the flow of fluids through vessels. This will make it possible to evaluate the effects of these parameters on the transport of microrobots to the target tumor, thus improving the accuracy of the approach.