1. Field of the Invention
The present invention relates to the use of back-scattered microwave radiation for non-invasive monitoring and diagnostics of biological activity, physiologic activity, anatomical structure and the pathology of various organs of living animals and man.
2. Description of the Prior Art
The use of microwaves in monitoring biological activity and pathological diagnostics is receiving more and more attention, particularly because microwaves are capable of penetration of soft tissue and can be used in non-invasive techniques for monitoring the heart, brain and other organs. Two examples of such techniques are disclosed in U.S. Pat. Nos. 3,483,860 to Namarow and 3,951,314 to Malech.
U.S. Pat. No. 3,483,860 to Namarow discloses a method for monitoring intrasomatic circulatory functions and organ movement wherein low power microwave signals are modulated with an audio frequency and transmitted through a horn antenna positioned on a subject's chest. A portion of such signals is reflected back and received through a directional coupler. The received signals are modulated in accordance with heart action, i.e. variations in blood flow during the pumping cycle and movement of the heart and adjacent bodily organs. The modulated signals are amplified and demodulated in a receiver, the modulation envelope being impressed on the audio carrier frequency. While providing an important diagnostic tool, because of the use of a horn antenna large areas are irradiated and it is not possible to isolate for diagnosis small localized areas. Also, since the system depends on variations in blood flow or muscle or heart movement, it cannot be used for medical diagnosis of areas such as the brain which is free from movement or the spine which is substantially transparent to microwaves.
U.S. Pat. No. 3,951,134 to Malech discloses a method and apparatus for remotely monitoring brain waves. Electromagnetic signals of different frequencies are simultaneously transmitted to the brain of the subject. It is suggested that the signals of different frequencies penetrate the subject's skull and mix to form an interference waveform which is modulated by brain activity. The modulated interference waveform is re-transmitted from the brain and picked up by the antenna and processed in received electronics to develop a signal representing intra-brain activity. While the Malech patent provides a means of monitoring brain function which may be a useful barometer of organic functions, it is too technically cumbersome to be accepted as a general diagnostic tool by the general practioner.
Over the years researchers have reported various techniques for using microwaves as a means for biological studies and reference may be made to the following publications.
(1) C. Susskind, "Possible Use of Microwaves in the Management of Lung Disease," Proc. IEE, Vol. 61, pp. 673-74 (May 1973);
(2) C. Susskind and A. R. Perrins, "Oscillograph Field Plotter," Electronics, Vol. 24, pg. 140 (September 1951);
(3) P. C. Pedersen et al., "An Investigation of the Use of Microwave Radiation for Pulmonary Diagnostics," IEEE Transactions on Biomedical Engineering, Vol. BME-22, pp. 410-12 (September 1976);
(4) P. C. Pedersen et al., "Microwave Reflection and Transmission Measurements for Pulmonary Diagnosis and Monitoring," IEEE Transactions on Biomedical Engineering, Vol. BME-25, pp. 40-48 (January 1978);
(5) D. G. Bragg et al., "Monitoring and Diagnosis of Pulmonary Edema by Microwaves: A Preliminary Report," Investigative Radiology, Vol. 12, pp. 289-91 (May-June 1977);
(6) D. W. Griffin, "MW Interferometers for Biological Studies," Microwave Journal, Vol. 21, pp. 69-72 (May 1978);
(7) H. P. Schwan, "Microwave Biophysics," Microwave Power Engineering, E. C. O'Kresss, ed. (Academic Press. 1968) pp. 213-34;
(8) O. M. Salati et al., "Radio Frequency Radiation Hazards," Electronic Industries, pp. 96-101 (November 1962);
(9) J. Yamaura, "Mapping of Microwave Power Transmitted Through the Human Thorax," Proceedings of the IEEE, Vol. 67, pp. 1170-71 (August 1978; and
(10) J. C. Lin et al., "Microwave Apexcardiography," IEEE Transactions on Microwave Theory and Techniques, Vol. MT-27, pp. 618-20 (June 1979).
While much research has been funded to develop microwave techniques for diagnostic testing and large amounts of funds have been spent in the development of sophisticated laboratory electronics to support such research, little attention has been paid toward the development of diagnostic instruments or tools capable of every day use by the general practioner. Perhaps one reason for the absence of interest in this area is the traditional reluctance of medical practioners in deviating from accepted practice and the use of tools or instruments radically different from those which have served the profession well over the years.