Changzhan Gu

Accurate Respiration Measurement Using DC-Coupled Continuous-Wave Radar Sensor for Motion-Adaptive Cancer Radiotherapy

Accurate respiration measurement is crucial in motion-adaptive cancer radiotherapy. Conventional methods for respiration measurement are undesirable because they are either invasive to the patient or do not have sufficient accuracy. In addition, measurement of external respiration signal based on conventional approaches requires close patient contact to the physical device which often causes patient discomfort and undesirable motion during radiation dose delivery. In this paper, a dc-coupled continuous-wave radar sensor was presented to provide a noncontact and noninvasive approach for respiration measurement. The radar sensor was designed with dc-coupled adaptive tuning architectures that include RF coarse-tuning and baseband fine-tuning, which allows the radar sensor to precisely measure movement with stationary moment and always work with the maximum dynamic range. The accuracy of respiration measurement with the proposed radar sensor was experimentally evaluated using a physical phantom, human subject, and moving plate in a radiotherapy environment. It was shown that respiration measurement with radar sensor while the radiation beam is on is feasible and the measurement has a submillimeter accuracy when compared with a commercial respiration monitoring system which requires patient contact. The proposed radar sensor provides accurate, noninvasive, and noncontact respiration measurement and therefore has a great potential in motion-adaptive radiotherapy.

Application of Linear-Frequency-Modulated Continuous-Wave (LFMCW) Radars for Tracking of Vital Signs

This paper focuses on the exploitation of linear-frequency-modulated continuous-wave (LFMCW) radars for noncontact range tracking of vital signs, e.g., respiration. Such short-range system combines hardware simplicity and tracking precision, thus outperforming other remote-sensing approaches in the addressed biomedical scenario. A rigorous mathematical analysis of the operating principle of the LFMCW radar in the context of vital-sign monitoring, which includes the explanation of key aspects for the maintenance of coherence, is detailed. A precise phase-based range-tracking algorithm is also presented. Exhaustive simulations are carried out to confirm the suitability and robustness against clutter, noise, and multiple scatterers of the proposed radar architecture, which is subsequently implemented at the prototype level. Moreover, live data from real experiments associated to a metal plate and breathing subjects are obtained and studied.

A Hybrid Radar-Camera Sensing System With Phase Compensation for Random Body Movement Cancellation in Doppler Vital Sign Detection

This paper presents a Doppler radar vital sign detection system with random body movement cancellation (RBMC) technique based on adaptive phase compensation. An ordinary camera was integrated with the system to measure the subjects random body movement (RBM) that is fed back as phase information to the radar system for RBMC. The linearity of the radar system, which is strictly related to the circuit saturation problem in noncontact vital sign detection, has been thoroughly analyzed and discussed. It shows that larger body movement does not necessarily mean larger radar baseband output. High gain configuration at baseband is required for acceptable SNR in noncontact vital sign detection. The phase compensation at radar RF front-end helps to relieve the high-gain baseband from potential saturation in the presence of large body movement. A simple video processing algorithm was presented to extract the RBM without using any marker. Both theoretical analysis and simulation have been carried out to validate the linearity analysis and the proposed RBMC technique. Two experiments were carried out in the lab environment. One is the phase compensation at RF front end to extract a phantom motion in the presence of another large shaker motion, and the other one is to measure the subject person breathing normally but randomly moving his body back and forth. The experimental results show that the proposed radar system is effective to relieve the linearity burden of the baseband circuit and help compensate the RBM.

Hybrid FMCW-interferometry radar system in the 5.8 GHz ISM band for indoor precise position and motion detection

A hybrid FMCW-interferometry radar sensor is presented. The proposed measurement system incorporates the linear frequency-modulated continuous-wave (FMCW) mode and the continuous wave (CW) interferometry mode. The radar system works in 5.8 GHz ISM band with a bandwidth of 160 MHz. Equipped with a special signal processing method, the hybrid system is capable of detecting absolute distance as well as slow motion. Experiments show that the absolute position detection has an average accuracy of 1.65 cm, and the accuracy of relative motion tracking is better than 2 mm.

A Self-Calibrating Radar Sensor System for Measuring Vital Signs

Vital signs (i.e., heartbeat and respiration) are crucial physiological signals that are useful in numerous medical applications. The process of measuring these signals should be simple, reliable, and comfortable for patients. In this paper, a noncontact self-calibrating vital signs monitoring system based on the Doppler radar is presented. The system hardware and software were designed with a four-tiered layer structure. To enable accurate vital signs measurement, baseband signals in the radar sensor were modeled and a framework for signal demodulation was proposed. Specifically, a signal model identification method was formulated into a quadratically constrained l1 minimization problem and solved using the upper bound and linear matrix inequality (LMI) relaxations. The performance of the proposed system was comprehensively evaluated using three experimental sets, and the results indicated that this system can be used to effectively measure human vital signs.

A multi-radar wireless system for respiratory gating and accurate tumor tracking in lung cancer radiotherapy

Respiratory gating and tumor tracking are two promising motion-adaptive lung cancer treatments, minimizing incidence and severity of normal tissues and precisely delivering radiation dose to the tumor. Accurate respiration measurement is important in respiratory-gated radiotherapy. Conventional gating techniques are either invasive to the body or bring insufficient accuracy and discomfort to the patients. In this paper, we present an accurate noncontact means of measuring respiration for the use in gated lung cancer radiotherapy. We also present an accurate tumor tracking technique for dynamical beam tracking radiotherapy. Two 2.4 GHz miniature radars were used to monitor the chest wall and abdominal movements simultaneously to get high resolution and enhanced parameter identification. Ray tracing technique was used to investigate the impact of antenna size in clinical practice. It is shown that our multiple radar system can reliably measure respiration signals for respiratory gating and accurate tumor tracking in motion-adaptive lung cancer radiotherapy.

Radar motion sensing for accurate tumor tracking in radiation therapy

Tumor tracking is important for radiotherapy treatment of lung cancer to deliver sufficient radiation dose without damaging the surrounding healthy lung tissue and causing severe side effects such as pneumonitis. However, conventional tumor tracking methods are either invasive to the patients or do not have sufficient accuracy. Radar physiological motion sensing provides a noninvasive and yet accurate way to track tumor during radiotherapy. The detection theory, system setup, and experiments are discussed in this paper. A tumor tracking algorithm that extracts accurate tumor position information from radar measurement result is also presented.

Analysis and Experiment on the Modulation Sensitivity of Doppler Radar Vibration Measurement

This letter analyzes the modulation sensitivity of Doppler radar vibration measurement using both 24 GHz and 2.4 GHz Doppler radars. A rigorous analysis is developed in terms of radar modulation sensitivity. In contrast to the common observation that the modulation sensitivity increases as the carrier frequency increases, it is shown that, for a given vibration motion, there exists a specific carrier frequency for optimal measurement. Experimental demonstration was carried out using both 24 GHz and 2.4 GHz radars to measure the same vibration, and the signal-to-noise ratio (SNR) at the receiver input was compared. It is shown that for cm scale movement, 2.4 GHz radar has a higher modulation sensitivity, while the 24 GHz radar has the optimal modulation sensitivity in the mm scale.

Doppler radar vital sign detection with random body movement cancellation based on adaptive phase compensation

This paper presents a Doppler radar sensor system with camera-aided random body movement cancellation (RBMC) techniques for noncontact vital sign detection. The camera measures the subjects random body motion that is provided for the radar system to perform RBMC and extract the uniform vital sign signals of respiration and heartbeat. Three RBMC strategies are proposed: 1) phase compensation at radar RF front-end, 2) phase compensation for baseband complex signals, and 3) movement cancellation for demodulated signals. Both theoretical analysis and radar simulation have been carried out to validate the proposed RBMC techniques. An experiment was carried out to measure a subject person who was breathing normally but randomly moving his body back and forth. The experimental result reveals that the proposed radar system is effective for RBMC.

A wireless multifunctional radar-based displacement sensor for structural health monitoring

Wireless smart sensor technology offers many opportunities to advance infrastructure monitoring and maintenance by providing pertinent information regarding the condition of a structure at a lower cost and higher density than traditional monitoring approaches. Many civil structures, especially long-span bridges, have low fundamental response frequencies that are challenging to accurately measure with sensors that are suitable for integration with low-cost, low-profile, and power-constrained wireless sensor networks. Existing displacement sensing technology is either not practical for wireless sensor implementations, does not provide the necessary accuracy, or is simply too cost-prohibitive for dense sensor deployments. This paper presents the development and integration of an accurate, low-cost radar-based sensor for the enhancement of low-frequency vibration-based bridge monitoring and the measurement of static bridge deflections. The sensors utilize both a nonlinear vibrometer mode and an arctangent-demodulated interferometry mode to achieve sub-millimeter measurement accuracy for both periodic and non-periodic displacement. Experimental validation results are presented and discussed.