By Nigel Whittle, Head of Medical and Healthcare at Plextek Ltd. Medical imaging is one of the most important technologies available to doctors and other medical workers, providing critical information for diagnosis and treatment. There is however no single technology for imaging of internal structures that is universally applicable to all tissues, has high resolution, is inexpensive, doesn’t use ionizing radiation, and creates images in real-time. An ideal system would also be portable and low-cost, with the potential for use in ambulances and other out-of-hospital environments. In recent years a substantial body of experimental work has been performed to apply microwave and radar technologies to the field of medical imaging and biosensing.
The microwave frequency band (300 MHz–30 GHz) possesses useful characteristics, including the use of non-ionizing radiation which is harmless at moderate power levels but penetrates biological tissue reasonably well. Compared with more conventional medical imaging systems such as MRI and X-ray, microwave systems generally a lower spatial resolution but a high temporal resolution (ie the ability to resolve fast-paced events).
Microwave medical imaging has been used for breast cancer screening. In this form it relies on differences in dielectric properties between the constituent tissues of the healthy and cancerous tissues in shallow parts of the body. It has also been investigated for stroke detection, bladder volume control, lung oedema, bone analysis and other possibilities.
However the problem with the approach is that human beings are essentially soft tubes of salty water and therefore quite conductive. This significantly reduces the penetration depth possible with radar, such that deeper screening within the body is not really viable.
With lower frequencies (4 – 8 GHz) it is possible to achieve some penetration, but this necessarily reduces the spatial resolution of the output image.
My colleague Damien Clarke, Senior Engineer at Plextek, provided me with the following insights: “This approach for breast cancer screening has been researched for at least a decade now. I know Bristol University has performed significant work in this area, though I don’t know if a clinical product is actually viable yet. Radar Tomography (RT), a new concept in medical imaging, has the potential to encompass all of the above criteria, and so curb radiation exposure, inconvenience, discomfort, and cost.”
Ultra Wide Band
Ultra-wideband (UWB) is a short-range wireless communication protocol, like Wi-Fi or Bluetooth, that uses short pulses of radio waves over a spectrum of frequencies ranging from 3.1 to 10.5 GHz. The allowable power limit has been set very low to avoid interference with other technologies that operate in this frequency band, while the wide bandwidth enables very fine time-space resolution.
Due to its features, UWB has the potential for medical monitoring, such as patient motion, wireless vital signs, and medicine storage monitoring. This monitoring function could be applied in intensive care units, post-operative environments, home health care, and paediatric clinics. The deployment of UWB vital signs monitoring system could also enable proactive home monitoring of elderly patients, which could decrease the cost of healthcare by allowing eligible patients to return home from hospital.
Perhaps more significantly, UWB has the potential to detect, noninvasively, tiny movements inside the human body. It could therefore use movement detection of the aorta or other parts of the arterial system to monitor cardiovascular physiology, or other parameters such as heart rate (HR), respiration motion, and blood pressure (BP). Imaging of surface and more deeply located structures such as breast tissue for cancer diagnosis is another promising application of UWB technology that has the potential of taking over the role of X-ray mammography.
A possible medical application of radar however is to measure chest motion without contact. By looking for particular frequency oscillations it is then possible to estimate heart rate (0.8 – 2 Hz) and respiration rate (0.1 – 0.5 Hz) simultaneously. It is also possible to detect shivering (< 14 Hz) and micro-shivering (7 – 11 Hz) though I don’t really know whether that is a useful diagnostic capability.
As the medical world turns its attention to long-term, mobile, and even home-based imaging and monitoring for preventive screening and early detection of diseases, radar-based biosensing and imaging applications are likely to play an increasingly important role.
Their advantages include potentially low cost and small size of the required hardware, plus a wide application across fields as diverse as heart rate tracking, sleep monitoring and fall detection for the elderly, right across to screening of the cardiovascular system, breast cancer imaging and stroke detection.
Compound Radar Approach for Breast Imaging
For more information or to discuss anything mentioned in this blog in further detail, please contact Nigel directly at firstname.lastname@example.org