Inside an MRI scanner, a plastic and ceramic robot works on a prostate. Image courtesy Gregory Fischer/WPI.
Metal objects as simple as a dime become deadly around an MRI machine, due to its intense magnetism. Built of plastic parts with ceramic piezoelectric motors, the small robot is designed to perform surgeries on patients within active MRI machines and is already in its testing phases.
“Essentially, we made a device that can move around the MRI bore without affecting image quality,” said Gregory Fischer, a professor of mechanical engineering at Worcester Polytechnic Insitute (WPI), in an article by Eliza Strickland for IEEE Spectrum.
Engineering Challenges
Fischer says one of the challenges in building the robot was ensuring its RF emissions didn’t interfere with the magnetic and electric fields used in MRI machines. The research team first experimented with pneumatic actuators to move the device. “If you use air there are no electrical signals, so it seems like it should be great,” Fischer says. But he wasn’t satisfied with the results. “It’s very hard to use air pressure to control things precisely—you get jitter and overshoot.”
Commercially available piezoelectric motors convert electrical signals into oscillations, which drive the robot. But despite being designed for low-power and low-cost, they are noisy, said lab member Hao Su. To get around this problem the team replaced the drivers with a new piezoelectric drive system using a direct digital synthesizer, generating precise waveforms to drive the actuator.
The group packed all the control electronics into a carrying case that sits beside the MRI machine, communicating with the robot via a fiber-optic cable. “You can bring it into any MRI room and have it up and running in an hour,” Fischer says.
How the MRI Procedure is Effected
The robot is currently performing prostate biopsies while in its testing phase. These procedures are typically imprecise says the trials principle investigator Clare Tempany, a radiologist and director of the National Center for Image Guided Therapy at Boston’s Brigham and Women’s Hospital.
Typically, a physician targets the prostate by placing a grid guide between the patient’s legs. The doctor inserts needles through the skin and into each quadrant to get usually between 10 to 50 tissue samples, risking infection. “This is somewhat disparagingly called ‘the blind biopsy,’” said Tempany. “There’s no lesion targeted, it’s just: ‘Let’s push a bunch of needles in and see what we get.’”
Using the MRI machine, doctors can now identify parts of the prostate that look suspicious and direct the robot to those spots. In current trials, the doctor takes the actual step of inserting the needle and typically takes samples in just four locations. “It’s a smarter biopsy,” Tempany said.
This low level of autonomy makes one wonder, can you really still call this device a robot? Fischer argues we can, as it senses where it is inside the scanner and positions its joints to move itself to the specified location. “It can locate the target, track the needle, and if it deflects during insertion, it can steer the needle to hit the target,” he says. “We’re taking baby steps to get the robot into clinical use.”
WPI’s Automation and Interventional Medicine Robotics Lab led the research. Fischer and his research partners are working with Acoustic Medsystems to commercialize the device for both prostate cancer diagnostics and treatment.
To learn more about the plastic robot, visit ieeexplore.ieee.org.