Robotic Help In High-risk Twin Pregnancies

In Switzerland, around 2,400 children are born as twins every year. When the foetuses share a placenta, they are connected to one another via blood vessels. If the blood circulation becomes unbalanced, this can be life-threatening for both, as too much blood flows from one foetus to the other. The condition known as 'twin-to-twin transfusion syndrome' (TTTS) affects around twenty to thirty women a year in Switzerland. To date, the only effective treatment is a highly complex operation that is performed by only a handful of specialists worldwide.

Researchers at ETH Zurich and doctors at the University of Zurich have set themselves the goal of making this operation easier and lifting its success rate. Currently, surgeons use a foetoscope for this purpose - a delicate endoscope designed for procedures on pregnant women. It contains a small camera and a channel through which a thin fibre guides laser light to the blood vessels in the placenta. In this way, surgeons are able to seal the vessels in the placenta that connect the two foetuses.

The fetoscopes in use today, however, are rigid. Depending on the position of the placenta, it can therefore be extremely difficult to reach all the affected blood vessels and seal them with the laser.

Magnetic control for greater manoeuvrability

In response to this situation the researchers and doctors have developed a flexible foetoscope with a diameter of just 3.2 millimetres, featuring a tip containing magnets. Three large electromagnets outside the patient's body generate a controllable magnetic field, enabling them to bend the tip of the foetoscope, whereby the magnetic field is entirely innocuous.

The principle is similar to that of a compass needle: just as a compass needle aligns itself with the Earth's magnetic field, the magnets in the tip of the fetoscope follow the externally generated magnetic field. If the magnetic navigation system changes direction, the tip of the instrument shifts as well. "We have achieved a bend of up to 173 degrees. This means we can easily reach even the hard-to-access vessels," says Michelle Mattille, a postdoctoral researcher and lead author of a external page paper recently published in the journal Science Robotics, which presents the new robotic platform.

Navigating with a panoramic view

The panoramic view is a second key component of the robotic platform. During minimally invasive procedures, surgeons can only see a small section of the surrounding area through the endoscope. Which means that they must therefore memorise the vessels they have already seen and the courses they run, which calls for a great deal of experience and concentration.

The new system combines the individual endoscopic images in real time to form a panoramic image, enabling the surgeon to now select a target on this two-dimensional map. The fetoscope then navigates there automatically. Doctors, however, can take control at any time and steer the fetoscope manually using a PlayStation game controller. Software then translates the desired movement in the camera image into the corresponding change in the magnetic field.

Mattille was surprised by the extent to which the robotic procedure differed from conventional laser surgery. "Even the very steady hand of an experienced surgeon causes the foetoscope to wobble slightly. Our robotic platform, on the other hand, stabilises the tip and holds it much more steadily at the desired location to coagulate the vessels precisely," as the researcher relates.

In experiments, the participants hit simulated targets far more accurately using the robotic system. "With the robotic system, the deviation was typically 140 micrometres, meaning it is more than four times more precise than conventional comparable instruments," Mattille states.

Critical testing outside the laboratory

An experiment on a pregnant ewe represented a key step towards the clinical application of the robotic platform. This marked the first time the researchers had left the controlled laboratory environment behind and tested the device under real-world conditions. They now had to contend with the animal's breathing and heart rate, cloudy amniotic fluid, as well as suspended particles and a moving foetus.

"We spent a year preparing for the approximately three-hour animal experiment. We were the first group to successfully replicate the key steps of the procedure," as Mattille states.

Mattille developed the platform as part of her doctoral work, collaborating with researchers from ETH Zurich and the surgeons Nicole Ochsenbein of the University Hospital and Ueli Moehrlen of the University Children's Hospital Zurich. Quentin Boehler, who worked on the project and now heads up the Medical Robotics Lab at ETH Zurich as Professor of Robotics, also played a key role.

Following the successful tests, the team now intends to further develop the platform for use on humans. In this context, the researchers must, above all, conduct further safety assessments and refine the algorithms to create a robust system for clinical use. At the same time, they are developing additional assistance functions designed to provide targeted support for surgeons during the ongoing procedures.

Also conceivable for other procedures

In future, the technology could also be used over and beyond the field of foetal surgery. One possible application would be to assist with navigation during gastroscopies and cystoscopies, while mapping the areas being examined. This would also allow changes over time to be tracked precisely. "The requirements are somewhat different there, however," says Mattille. "Instead of a relatively flat surface, as with the placenta, here, a three-dimensional cavity needs to be mapped."

The successful in vivo animal trial represents an important milestone on the path to robot-assisted procedures in foetal surgery: for the first time, researchers have succeeded in demonstrating the key steps of an TTTS procedure in a realistic environment. For Mattille, the motivation is clear: "Although TTTS affects only a small share of twin pregnancies, the procedure is a matter of life and death for these children."