Scientists are investigating a new, contact-free method to monitor breathing during medical imaging and radiation therapy. A recent study in Medical Physics examines how 24 GHz millimeter-wave sensors (MWS) could provide a non-invasive way to track respiratory motion in patients undergoing X-rays and CT scans. The research team evaluated the sensors’ directional accuracy, developed a respiratory monitoring system, and assessed their potential for clinical applications.
Study: Exploring the feasibility of millimeter-wave sensors for non-invasive respiratory motion visualization in diagnostic imaging and therapy. Image Credit: Studio Romantic/Shutterstock.com
Background
Accurate respiratory motion monitoring is crucial in radiation therapy, ensuring precise dose delivery while minimizing exposure to surrounding organs. In diagnostic imaging, especially CT scans, confirming a patient’s breath-hold is essential for obtaining high-quality images. Despite its importance, respiratory monitoring systems are primarily used in radiation therapy and have yet to be widely implemented in diagnostic imaging.
Traditional monitoring methods, such as contact-based pressure sensors and infrared cameras, can be uncomfortable and impractical for patients. Millimeter-wave technology, however, enables non-contact monitoring, offering a more convenient and less intrusive alternative. Previous studies have demonstrated MWS’s ability to track surface movements accurately, highlighting its potential for clinical use.
Study Overview
To evaluate MWS’s performance in capturing respiratory motion, researchers first assessed its directional capabilities using a radio-wave dark-box system. The results indicated azimuthal and elevational beamwidths of approximately ±20 degrees and ±40 degrees, respectively.
To refine the respiratory waveforms, the study applied a fast Fourier transform threshold and bandpass filtering to enhance signal quality. The researchers then tested the system with a respiratory motion phantom (QUASAR), which simulated controlled breathing patterns. By comparing the waveforms detected by MWS with those from the QUASAR device, they confirmed the sensor’s accuracy.
Moving beyond controlled settings, the study also monitored respiratory patterns in 20 healthy volunteers of varying ages, including infants and young children. The sensors were positioned for both supine and standing postures during chest CT and X-ray imaging, ensuring minimal movement from external sources.
Additionally, researchers evaluated the MWS’s ability to detect breath-holding in 18 volunteers. The sensors successfully recorded stable plateau signals, confirming their effectiveness in tracking breath-hold periods.
Key Findings and Implications
The results demonstrated that MWS effectively monitors respiratory motion with high accuracy. By fine-tuning acquisition parameters—such as sensitivity settings, noise reduction, and frequency optimization—the detected waveforms closely matched those recorded by the QUASAR phantom across all tested amplitudes.
One of the significant advantages of MWS is its ability to confirm breath-holding in different imaging scenarios. The stable signals recorded during breath-holds aligned with visual breathing cycle counts in infants and children, reinforcing the sensor’s reliability in clinical use.
Compared to traditional respiratory monitoring systems, MWS offers several benefits. Its non-contact approach eliminates patient discomfort and minimizes the risk of interference from physical sensors. Additionally, its compact design and ease of installation make it adaptable for various clinical environments, from routine radiology to advanced radiation therapy procedures.
Conclusion
This study highlights millimeter-wave sensors as a promising non-invasive solution for respiratory motion monitoring in both diagnostic imaging and radiation therapy. The 24 GHz MWS demonstrated strong precision, directional accuracy, and consistency in detecting breathing patterns across diverse conditions.
As healthcare continues to adopt advanced technologies, integrating MWS into routine clinical practice could improve imaging accuracy by enabling real-time respiratory monitoring. Future research should explore broader clinical applications, assess performance across diverse patient populations, and refine system integration to enhance imaging and treatment outcomes.
Journal Reference
Kosaka H., Kubo K., et al. (2025). Exploring the feasibility of millimeter-wave sensors for non-invasive respiratory motion visualization in diagnostic imaging and therapy. Medical Physics 1-9. DOI: 10.1002/mp.17616, https://aapm.onlinelibrary.wiley.com/doi/10.1002/mp.17616