A robotic device is expected to improve patient comfort and lung-biopsy accuracy. Currently, a lung biopsy calls for a surgeon to inserts a needle into a patient, aiming for a location specified in terms of millimeters or less based on a CAT scan. Unfortunately, surgeons are only accurate to within centimeters, so a patient must often endure repeated attempts by surgeons as they try to insert a 10 to 20-cm long needle into just the right spot to take a sample. It typically takes 10 tries before the surgeon hits the target.

A surgeon in Massachusetts noticed the discrepancy between his accuracy and that of the targeting data and wondered if biopsies could be made more accurate. After working with an engineering team from MIT, he came up with Robopsy, a robotic lung biopsy device.

The device consists of two concentric hoops at right angles and one atop the other. A carriage that holds the needle mounts above both hoops but is also connected to both. The top hoop controls how far right or left the carriage will be positioned. The other adjusts the height of the carriage relative to the patient, i.e., closer to or farther from the patient's head. As the hoops revolve about their long axis, they position the carriage and needle. Each hoop is turned by a motor from MicroMo Electronics Inc., Clearwater, FL, (micromo.com).

A similar motor turns a pinion that moves a gripping roller toward or away from an insertion roller, which is also powered by a small MicroMo motor. When the gripping roller is moved closest to the insertion roller, the two rollers hold the needle in place. Then, when the insertion roller turns, it drives the needle into the patient. Test showed it takes about 5 N to force a needle through the pleura (sac around the lungs). Therefore, the design team adjusted the device so that the insertion roller would put no more than 10 N behind the needle.

Each of the four motors is coupled to a 10-mm diameter, 256:1 gearbox. Encoders on the motors provide feedback for closed-loop positional control.

Parts of Robopsy are disposable. These include the hoops, base, and carriage. They are constructed of radiolucent plastics. The motors, which are metal, are located away from the hoops so they do not interfere with x-ray imaging used to help surgeons ensure the biopsy needle hits its target.

In a typical procedure, doctors use CT scans to determine where to place the Robospy and what path (angle and depth) the needle should take. Once the device is fastened to the patient, a second scan lets the system “see” or register the needle and set up to match the proposed path. The needle is inserted, but just before piercing the pleura, a third scan lets surgeons make fine adjustments. Then a fourth and final scan confirms the needle is in place.

Currently, the device can target a 1-cm lesion. The goal is to make it able to zero in on a 0.5-cm target.