Radar technology has also captured the imagination of engineers working in medical applications, with medical radar systems applied to heartbeat and respiration monitoring, as well as for breast cancer detection. Both CW Doppler radar and pulsed UWB radar systems have been proposed for medical applications, for remote patient monitoring. For example, the Virtual Medical Assistant (VMA) from Sensiotec, Inc. employs UWB radar technology for remotely measuring patient heart and respiration rates and patient movement, without implants, electrodes, or sensors contacting the patient. The system, which acquires data every two seconds, works with a light-weight sensor panel that is placed within about five feet of a patient. It emits nanosecond UWB pulses that penetrate the body, with reflected signals from the torso, heart, and lungs detected, filtered, and processed to produce medical data on the patient’s body movement, respiration, and heartrate.
The patient data is readily available by wired or wireless networks to multiple care-givers, such as doctors and nurses, and special alerts can be programmed for patients with critical heart and respiratory rates. For caregivers, this can mean reduced monitoring costs and increased productivity. For patients, this type of medical radar technology represents freedom from wires and sensors, as well as the elimination of skin tears from adhesive-affixed sensors.
2. This W-band radar system uses a three-channel antenna with dielectric lenses to allow close-up monitoring of bodily functions in medical applications. (Photo courtesy of the Fraunhofer Institute.)
Researchers at the Fraunhofer Institute have developed a prototype radar system that works at millimeter-wave frequencies from 75 to 110 GHz. The W-band radar employs a three-channel antenna with dielectric lenses (Fig. 2); it is capable of penetrating all dielectric, nonmetallic, and nontransparent materials and identifying small objects with fine precision.The radar is suitable for a wide range of applications, from industrial monitoring to medical technology. The W-band system, which is about the size of a cigarette box, is a modular and cost-effective design. Based on gallium-arsenide (GaAs) semiconductors, its use of antennas with dielectric lenses allows it to capture data from objects both close as well as far from the antennas. Measured data can be transferred to a computer via Universal-Serial-Bus (USB) interface.
Bristol University spin-out Micrima (Bristol, UK) is developing a medical imaging system that can distinguish a breast tumor from normal tissue by detecting the difference between their dielectric properties. Micrima is applying pulsed radar technology to trying to find breast tumors. The firm’s multistatic array processing for radio-signal image acquisition (MARIA) technology is based on a multistatic radar.
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The approach synthesizes an UWB pulse with a microwave vector network analyzer (VNA) sweeping in frequency from 4 to 10 GHz. The signal is transmitted from each element in a multiple antenna array and then received by all the other elements. The large aperture and wide bandwidth theoretically allow collection of reflected and scattered signals from objects as small as 1.7 mm. A three-dimensional image of the breast is constructed after the radar-return signals have been received. Transmitted signals have a peak power level of less than 1 mW, so the system is completely safe.
Since breast tumors can be distinguished from healthy breast tissue by differences in dielectric constant, the use of radio-frequency signals makes it possible to develop images for cancerous cells. The system, which is undergoing extensive clinical testing, was initially simulated by means of computer models before developing the experimental hardware. Micrima’s ultimate goal is to create a compact, low-cost version of the MARIA system that could be situated in surgeries and mobile screening units.
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