Researchers have programmed an MRI scanner to simultaneously monitor magnetized particles while propelling them through blood vessels as a means to locally deliver drugs.
Existing approaches combine the magnetic force from an MRI scanner with the force produced by particle collisions. But traditionally, it’s challenging to image using the MRI scanner and propel the particles forcefully enough to overcome blood flow.
“Steering particles in the bloodstream is akin to whitewater rafting: You have limited paddling ability compared to the strength of the river, so you need to position yourself appropriately in the flow to follow your desired path,” Boston Children’s Hospital bioengineer lab head said, according to the hospital. “In the existing approach, the MR scanner had to be programmed to alternate between imaging the particle and propelling it. This is really inefficient since whenever you are imaging, you are not propelling and vice versa. It’s like pushing a car up the hill and continuously stopping and starting. Half the time no one is doing anything.”
In a study published in Scientific Reports last week, researchers detailed how they reprogrammed the MRI scanner to harvest more of its energy for propulsion. They engineered the magnetic gradients of the scanner to push only in the desired direction and they programmed the scanner to image in the direction of propulsion, instead of 3 dimensions.
“When steering in the bloodstream, you typically have a map of the vasculature from pre-operative images,” Dupont explained. “You don’t need to measure location in three dimensions, since the particles are constrained to move inside the blood vessels. All you really need to know is where a particle is along the vessel. When the particle approaches a branching point, you want to propel it toward the desired branch and know where it is with respect to the branching direction. This can also be measured in one dimension.”
The reprogrammed scanner can generate 90% of its maximal propulsion force at a given imaging rate, the hospital reported. While they successfully navigated a millimeter-sized particle through branched blood vessels, they will need to repeat the trial with micrometer-sized particles, which are more useful for drug delivery applications. The team also did not address issues of drug release or localization.
“For therapeutic purposes you want to be on the micron scale,” Dupont said. “This will pose challenges in coordinating the steering of groups of particles and in determining what concentrations of particles are needed for visualization.”
