Late one crisp October night in 2006, a hospital technician in Montreal slid the limp body of an anesthetized pig into the tube of a magnetic resonance imaging machine, or MRI. A catheter extended from a large blood vessel below its neck—a carotid artery. Into the catheter, a surgeon injected a steel bead slightly larger than the ball of a ballpoint pen.

In a room next door, my engineering graduate students and I held our breath. We were testing a program designed to manipulate the machine’s magnetic forces, which would guide the bead like a remote-controlled submarine. Or so we hoped.

On a computer screen, the bead appeared as a square white tracking icon perched on the gray, wormlike image of the scanned artery. We stared at the square and waited. Nothing. Seconds ticked by, and still the bead refused to budge. Then suddenly the room erupted in cheers as we clapped our hands to our mouths and pointed at the screen. There, the bead was hopping up and down the artery, tagging every waypoint we had plotted. [read more..]