A Non-Invasive Path to Animal Welfare: Contactless Vital Signs and Activity Monitoring of In-Vivo Rodents Using a mm-Wave FMCW Radar

TL;DR

This work demonstrates a contactless, radar-based system for in-cage monitoring of freely moving rodents, combining a low-power 60 GHz FMCW radar with a DSP pipeline to simultaneously track position, activity, and respiration. By employing two runtime-configurable FMCW modes and RAF clutter suppression, the approach achieves high respiration-rate accuracy and reliable movement/ranging in single- and multi-animal settings. Heart-rate extraction remains challenging in awake, group-housed rodents, though respiration tracking is robust and consistent across cage conditions. The study emphasizes welfare improvements under 3R principles and lays groundwork for scalable, automated preclinical monitoring using compact embedded radar hardware.

Abstract

Monitoring physiological and behavioral parameters of laboratory rodents is fundamental for biomedical research, yet conventional techniques often rely on invasive sensors or frequent handling that can induce stress and compromise data fidelity. To address these limitations, this paper presents a contactless and non-invasive in-vivo monitoring system based on a low-power 60 GHz frequency-modulated continuous wave (FMCW) radar. The proposed system enables simultaneous detection of rodent activity and vital signs directly within home-cage environments, eliminating the need for implants, electrodes, or human intervention. The hardware platform leverages a compact Infineon BGT60 series radar sensor, optimized for low power consumption and continuous operation. We investigate sensor placement strategies and design a complete signal processing pipeline, including range bin selection, phase extraction, and frequency-domain estimation tailored to rodent vital signs. The system achieves 3 cm and 0.1 m/s sensitivity for motion and activity detection, while allowing discrimination of micro-movements associated with cardiopulmonary activity with a 2 um distance resolution. Experimental validation with two rodents in realistic in-vivo cages demonstrates that the radar can track animal position and extract respiration rates with 2 bpm accuracy. By minimizing stress and disturbance, this work improves both animal welfare and the reliability of physiological measurements, offering a refined alternative to traditional monitoring methods. This work represents the first demonstration of continuous radar-based vital sign monitoring in freely moving rodents within group-housed cages. The proposed approach lays the foundation for scalable, automated, and ethical monitoring solutions in preclinical and translational research.

Figures (9)

• Figure 1: System setup overview for validation and in-vivo tests. The ideal distance is disccused in \ref{['sec:idealdistance']}, velocity is defined in \ref{['eq:omega']}-\ref{['eq:vres']} and range $d$ in \ref{['eq:submillimeterdisplacements']}. The filtered area highlights the area in which vital sing monitoring and tracking are active, signals coming outside this region are not considered.
• Figure 2: Filed analysis of signal reflection depending on the distance between the radar antennas and the cage plastic. Normalized signal strength is measured in dBFS (decibels relative to full scale). The optimal distance range for all the three antenna is highlighted between 34.
• Figure 3: Ranging of a puppet target over time, represented as a series of one range-doppler maps per second. The sequence is recorded as part of the validation process in controlled conditions during a movement segment. The intense color represent the target.
• Figure 4: A. Empty cage. B. Cage filled with all internal elements. C. Filled cage complete of external metallic rack support. 1. Cage conditions. 2. Radar's average frame power during movement validation. In the blue rectangles the first movement segment and in the green rectangles the second movement segment. 3. FFT of the target vibration signal sensed with the radar. The gray dashed line indicates the frequency of the FFT's peak, corresponding to the measured target vibration frequency.
• Figure 5: Setup for in-vivo experiments at ETH EPIC center. The two interlinked cages (model GM500 from Tecniplas) are mounted on a local changing station, allowing both mice to freely access either cage at any time during the experiment. Occasionally, the mice voluntarily separated themselves between the two cages, enabling "single-mouse" experiments to be conducted. The radar is placed at 3.5 to the cage, connected to a local workstation for data collection and synchronization with the image-based ground-truth. (A) Lateral view of the cage environment with metallic nets, internal plastic and the Swiss Webster; (B) Cages top view; (C) The BGT60UTR13DAiP radar electronic board used for the in-vivo experiments; (D) Ideal distance to cage technicality.