Radar instead of stethoscope for detection of heart sounds?

The radar system measures heart sounds contactlessly. (c) FAU / Kilin Shi)

Engineers have developed a procedure for reliably detecting and diagnosing heart sounds using radar. Mobile radar equipment could replace conventional stethoscopes in the future –  a permanent touch-free monitoring of vital signs with stationary radar is also possible.

Researchers at the Friedrich Alexander University of Erlangen-Nuremberg (FAU), in collaboration with the Brandenburg Technical University (BTU) Cottbus and the Department of Palliative Medicine at the University Hospital Erlangen, have developed a method that could one day replace classical phonocardiology: by means of a so-called six-factor cusp radar system they measure skin vibrations caused by the heartbeat. “In principle, we’re using a similar method to detecting speed in road traffic,” explains Christoph Will, PhD student at the Department of Technical Electronics (DTE) in Erlangen. “During this process, a radar wave is aimed at the surface of an object and reflected. If the object moves, the phase of the reflecting wave changes. This is used to calculate the strength and frequency of the movement – of the chest in our case.” Unlike the traffic surveillance radar, the biomedical radar system is capable of detecting movement changes in the range of a few micrometres – an important prerequisite for diagnosing even the smallest anomalies, e.g. insufficiencies, stenoses or heart valves that do not close properly.


Initial trials were very successful: the test patients were examined in various states of activity such as while resting and after sports and their heart sounds were detected. A direct comparison of the radar system with conventional standard instruments – a digital stethoscope and an electrocardiograph (ECG) – showed a very high correlation. “For example, when diagnosing the S1, the first heart sound, we achieve a 92 percent agreement with the ECG. In the direct comparison of waveforms with the digital stethoscope, the correlation is 83 percent. This is absolutely reliable,” says Kilin Shi, also a PhD student at DTE. The researchers say that the slight deviations are caused by the fact that measurements using the radar system and the reference systems cannot be carried out simultaneously on exactly the same place on the body. In addition, the radar system measures a surface area and not a single spot like the stethoscope, which is also a reason for the varying measurement values.

Touch-free and objective

The red rays indicate where to measure. (c) FAU/Kilin Shi

The FAU researchers are optimistic that mobile radar systems could replace conventional stethoscopes in diagnosing heart function in the near future. A significant advantage offered by radar is the fact that the values are recorded digitally and are thus not subjective allowing human error to be increasingly ruled out during the diagnosis of anomalies or diseases. Using biomedical radar systems for automated prophylactic examinations for example in doctors’ waiting rooms, at work, or at home, is also feasible.

The researchers are already working on another project for monitoring the vital functions of patients who are seriously ill using stationary radar systems around the clock and without disruptive cables. “Touch-free and therefore stress-free measurement of vital parameters such as heart sounds has the potential to revolutionise clinical care and research, for example, in palliative medicine,” explains Prof. Dr. Christoph Ostgathe, Head of Palliative Medicine at Universitätsklinikum Erlangen at FAU and co-author of the study. “For example, we could inform relatives of terminally ill patients more quickly at the beginning of the dying phase, as the radar system immediately detects any changes in patients’ health. It would also be possible to detect any painful symptoms in patients who cannot communicate”.

Source: Friedrich-Alexander-University Erlangen-Nuremberg