Groundbreaking technology uses quantum sensors to measure heart activity

Physicists at Johannes Gutenberg University Mainz (JGU) have developed a groundbreaking technology that uses quantum sensors to measure biomagnetic signals, such as heart activity. Researchers from the DIAQNOS (DIAmond-based Quantum Sensing for NeurOSurgery) flagship project, funded by the German Federal Ministry of Research, Technology, and Space, and coordinated by Dr. Arne Wickenbrock in Mainz, have demonstrated the potential of quantum technology for future medical applications. To this end, researchers in the group led by Prof. Dr. Dmitry Budker - a member of the PRISMA⁺⁺ Cluster of Excellence and the Helmholtz Institute Mainz - used nitrogen vacancies (NV) in diamonds, as reported in a recent article in the journal Science Advances. Muhib Omar, a doctoral student in Budker's research group and the coordinating author of the article, developed the new quantum sensor during his doctoral research. Thanks to its compact size and its ability to function at room temperature, this NV-based sensor opens up new avenues for improving the measurement of magnetic signals from the heart or the brain. It could be used for the early detection of conditions such as myocarditis or epilepsy.

NV centers form when a vacancy in the diamond lattice is located directly next to a nitrogen atom that has been incorporated into the diamond in place of a carbon atom. By observing the energy levels of these centers, researchers can measure a wide range of physical phenomena such as magnetic or electric fields, temperature, and mechanical stress with high precision.

These results are the product of over ten years of development work. We work closely with neurosurgeons to ensure that our technologies do not remain confined to the laboratory but find clear practical applications. Our primary goal is to develop highly sensitive sensors that function outside the laboratory and can fulfill important societal needs."

Dr. Arne Wickenbrock, Johannes Gutenberg University Mainz

The researchers of the DIAQNOS project used three systems developed independently by the project partners JGU, the Universities of Stuttgart and Freiburg, as well as by the startup Q.ANT GmbH, to measure the heart's magnetic field. In doing so, they demonstrated that quantum technologies in Germany are ready to take the important step toward medical applications and identified the improvements still needed to achieve this. The fiber-based NV-diamond magnetometer developed by JGU was designed as a portable endoscope and operates without a magnetic bias field. This is in contrast to the other two systems, that use such fields to filter out magnetic interference from the environment.

Developing a new way of detecting heart signals

There are currently two common methods to measure heart activity: electrocardiography (ECG) and magnetocardiography (MCG). While ECG uses electrode patches applied to the patient's skin to measure the electrical activity within the heart, MCG methods detect magnetic fields. ECG is widely used, but susceptible to the differing conductivity of body tissues. Certain medical scenarios, such as burn wounds, can also make it impossible to place electrodes on the skin directly. In contrast, MCG needs no contact with the skin and is only minimally influenced by tissue conductivity. Since the method requires highly sensitive magnetometers, it has historically relied on high-cost, complex technologies such as superconducting quantum interference devices (SQUIDs), and optically-pumped magnetometers (OPMs).

The system from the JGU group, based on NV centers in diamonds, is an alternative that offers significant advantages over existing MCG methods. The most important difference is the small size of the sensor: a truncated diamond pyramid with a volume of less than 0.5 cubic millimeters, which makes it easy to transport. Another advantage is that, unlike SQUID or OPM based systems, NV magnetometers operate at room temperature. This makes them suitable for direct use on the patient's skin and allows them to be applied at any desired location. This opens up the possibility of more precise mapping of biomagnetic signals, such as 3D reconstruction of the heart's electrical conduction system or the measurement of fetal heart activity. "NV magnetometers are characterized by fast initialization, excellent biocompatibility, and stable operation over a wide temperature range. This makes them particularly attractive for biomedical applications," summarized Arne Wickenbrock.

The potential is high but technical challenges remain

While the study shows the promise of NV diamond magnetometers, there remains a performance gap compared to SQUIDs and OPMs, which still offer higher sensitivity and better signal-to-noise ratios. However, as development progresses, application possibilities beyond the clinical field are opening up: the unique combination of a wide dynamic range, noise suppression, and scalable geometry makes NV magnetometers suitable for various novel biomedical applications.

Thanks to their compact size, the detectors can be easily combined with improvement mechanisms that could enable them to achieve ECG-like quality. One example of such mechanisms are so-called flux concentrators: structures that can concentrate the magnetic flux within the diamonds and thereby amplify magnetic signals. Thanks to the small volume of the NV sensors, amplifications of more than a factor of 100 can be achieved. The research and development of flux concentrators that function at room temperature is one of Muhib Omar's main areas of focus. "Adapting magnetic structures to optimally concentrate the magnetic field lines from a source within the diamond is the path to bringing these quantum technologies into practical use." Another area of application is surgical oncology. In this context, the difference in magnetic field between two spatially separated sensors forming a gradiometer is measured. The method also supports intraoperative nerve monitoring in unshielded environments. The spatial sensitivity to field gradients also facilitates, for example, the noninvasive separation of maternal and fetal heart signals for prenatal monitoring. Above all, NV gradiometers could enable portable magnetoencephalography systems to operate at room temperature, thereby opening up new possibilities for neurological diagnostics or next-generation brain-computer interfaces (BCIs).