Using magnetic particles has an additional benefit. Magnetic resonance imaging (MRI) scans can detect the therapeutic nanoparticles, potentially allowing researchers to estimate how much of the drug has been absorbed into the brain.

Clinical use of the technique, however, is still a long way off. "If we want to push this method to clinical trial, several problems must be resolved," Wei says. The system has to be scaled up to be used on larger animals--not an easy proposition, since the magnetic fields must penetrate more deeply to reach their brains. The entire process must also be fine-tuned so it can be replicated precisely, over and over. The magnetic field technology must be honed to make it both more portable and more accurate, to ensure that it doesn't attract toxic particles to anywhere other than the cancerous tumors. And the focused ultrasound technology has yet to be proven effective at blood-brain barrier disruption in the larger, thicker human brain, let alone safe.

"I applaud them for what they're doing," says Pierre Mourad, a physicist who specializes in medical acoustics at the University of Washington in Seattle. "They've managed to do an exhaustive first pass at a novel way of addressing the difficult problem of increasing dose delivery into the brain."

But Mourad says he's disappointed that the group focused strictly on brain tumors. "For many malignant primary brain tumors, increased uptake of drug into the tumor isn't the problem." Rather, he says, even after a malignant tumor has been surgically removed, there are still cancerous cells throughout the brain that can cause a recurrence of disease. The magnetic-targeting method only directs therapy to tumors that are visible, leaving the rogue cells behind.

"I'd want to solve movement disorders with these procedures," Mourad says--diseases such as Parkinson's and Alzheimer's, in which very discrete bits of the brain go bad. Parkinson's, for instance, typically affects distinct, well-known locations. "There are decent drugs to address it, but delivery and dose is the big problem," says Mourad. "That's where I would go first with this exciting technology."

Brigham and Women's McDannold also sees broader applications. "Technology that can get drugs into the brain where we currently can't, and deliver them in a controlled way, opens up possibilities for drugs of all types," he says.