Self-driving needle steers its way through living lung tissue

The lungs are one of the most difficult organs for physicians to navigate, featuring a dense network of blood vessels, bronchi and other critical anatomical structures that makes reaching distant lung nodules with a conventional bronchoscope challenging. To overcome these limitations, researchers at The University of North Carolina at Chapel Hill, Vanderbilt University and The University of Utah built a compact robotic system that can autonomously steer a flexible needle around these anatomical obstacles within the lungs of live animals (in this case pigs), which they described in the journal Science Robotics.

Designing the robot

The least invasive way to diagnose lung nodules is bronchoscopy, a procedure where a physician navigates an endoscope through the patient’s mouth and through the airways. From there, a straight needle is inserted into the lung tissue to a target site, removing a small sample of the nodule for analysis.

However, current manual bronchoscopy techniques have several limitations. Straight needles aren’t designed to navigate around anatomical obstacles and through lung tissue that moves when people breathe. These barriers have limited biopsies of small nodules or nodules deep within the lungs and further away from the major airways — and while robot-assisted bronchoscopy has made strides in reaching distant nodules, a physician must still operate the bronchoscope, and current systems do not offer needles that can steer through lung tissue.

“We are trying to target an object the size of a pea that’s moving when the person breathes, so it’s like trying to hit a moving target that’s very small,” said Dr Jason Akulian, study co-author and a pulmonary interventionist at UNC-Chapel Hill.

The researchers addressed these limitations when they designed their semi-autonomous robotic system. The system has three stages, with the first two requiring a physician to insert a bronchoscope into the airways and then operate an aiming device (in conjunction with the software) to launch the needle at a desired target in the lungs. The last stage is where the robot autonomously steers the needle to its destination.

The system’s hardware components include flexible laser-patterned needles that curve around anatomical obstacles, a mechanical control of the needle thrusting and turning, and an aiming device. Its software independently operates the needle steering and semi-operates the aiming device. Using a 3D map of the pig’s lungs acquired from a previous computed tomography (CT) scan, it plans the shortest route for the steerable needle to take that safely avoids obstacles such as blood vessels and accounts for respiratory motion caused by the animal’s breathing.

Illustration of the robotic system’s hardware used to deploy the steerable needle into the lungs. Image credit: Alan Kuntz et al.

Testing its performance

The researchers wanted to test how well the autonomous system controlled the needle steering in living, breathing lung tissue, which is more challenging to navigate than deceased lung tissue or phantom lung tissue. The first set of experiments assessed whether the robot-steered needle accurately followed a pre-planned route in the living pig lung tissue.

The results from three needle deployments showed the automated steering stuck to the route with only small deviations. The steerable needle safely avoided anatomical obstacles and reached the targets with an average error of 2.7 mm. The smallest nodule physicians will attempt to biopsy is about 8 mm in diameter, so the result fell well within the target range of an actual biopsy.

The second set of experiments compared the accuracy of the robot-steered bronchoscopy needle in ex vivo lung tissue with a manual diagnostic bronchoscopy technique. The results of 21 total needle deployments showed that, on average, the robot-steered needle had a significantly lower targeting error (about 3.5 mm) than the manual tool (about 13 mm).

“This is the biggest milestone we’ve reached so far,” said Professor Ron Alterovitz, principal investigator of the study, from UNC-Chapel Hill. “This robot is the first one that has autonomous needle steering, worked in vivo, and could avoid anatomical obstacles.”

Indeed, the robot-steered bronchoscopy needle consistently outperformed the physician-guided bronchoscopy needle in reaching the selected targets, and the targeting errors were so small that the robot could be used to biopsy the smallest clinically relevant nodules. The study thus demonstrates “the potential for improving the accuracy of medical procedures when using medical robots with autonomous capabilities”, according to Alterovitz.

The researchers plan to test their robot next in human cadaver lungs, followed by live human trials. They also plan to fully automate the operation of the aiming device, with the ultimate objective of leveraging their technology to improve patient care.

Top image: Robot components, including the steerable needle, bronchoscope and actuation unit.