Over the years, microwave energy has been applied to a variety of different medical applications, from analysis of internal organs to direct treatment of cancerous tumors, and even in surgery.
| 1. The microwave hyperthermia applicator on the left was designed for use at 2.45 GHz to treat close-to-the-surface tumors, while the applicator on the right, for use at 27 MHz, was developed for more deeply seated tumors. |
By the mid-1960s, the potential of microwave systems similar to those used in warfare was being evaluated for the then-emerging health-care industry. In 1967, the Cornell Aeronautical Laboratory, Inc. (Buffalo, NY) was using a low-power coherent-detection X-band radar system, with separate antennas for transmit and receive functions, to track body motionfor example, to alert a nurse if a patient's heart had stopped. By taking measurements of a patient's pulse and respiration, it was hoped that an analysis of the waveforms could be used to find signs of emotional or physical stress.
The X-band radar system employed a klystron with 400-mW continuous-wave (CW) output-power at 9375 MHz for both transmit power and local-oscillator (LO) power for downconversion of return signals in the receiver. Since the actual output power of the tube was only 60 mW, it posed no danger to the patient or to hospital staff. The transmit signals were reflected by both moving and non-moving surfaces, and the receiver analyzed the received signals for phase shifts caused by the moving surfaces. Although the system was intended for hospitals, the US Air Force was also interested in the system for use in monitoring pilots or astronauts.
| 2. This microwave scapel applies S-band energy to coagulate the area around a cut tissue and control bleeding during surgery. |
By the 1980s, cancer had become a leading health concern. Some firms involved with high-frequency electronics explored whether some form of electronic-based system might provide a way to combat cancerous growths in human patients. In July 1981, a special report by Associate Editor Walter Bojsza focused on work by Dr. Fred Sterzer of the Microwave Technology Center within RCA Laboratories (Princeton, NJ). Sterzer's main interest was in the use of microwave hyperthermia for treating cancer. Although it had become clear to the firm's upper management that this was not an area that showed promise as a revenue, RCA generously supported the work of Sterzer and Bob Paglione, who designed many of the microwave applicators for treating patients.
Continue on Page 2
For example, Sterzer and Paglione had designed an applicator at 2.45 GHz for treating breast tumors, and another applicator at 27 MHz for treating more deep-seated tumors (Fig. 1). The principle behind their application of microwave energy was in the way that different cells would dissipate the heat produced by the incident energy. Above a certain temperature, all cells will die. But healthy cells are more efficient at dissipating heat than cancer cells. Microwave hyperthermia would, in theory, destroy cancerous cells while leaving behind the healthy surrounding tissues. The two cancer fighters worked with the assistance of the Radiotherapy Department at New York's Montefiore Hospital.
Above and beyond cancer research, RCA was helpful to the health-care industry in other ways. For example, the company worked on one of the early satellite-communications-based data links to arm doctors in New York City and Los Angeles with rapid feedback on a patient's electrocardiograms (EKGs). RCA's satcom links were used to send EKGs from hospitals in the two cities via the Telemed Cardio-Pulmonary System for computer analysis at Hoffman Estates (Chicago).
In the early 1980s, Microwave Associates (Burlington, MA) developed a dual-mode microwave system to diagnose and treat cancer noninvasively. The system employed a sensitive radiometer receiver that measured temperature deviations of less than 0.1C and a transmitter that coupled microwave energy into the body. The system was being evaluated with cancer patients at Norfolk (VA) General Hospital. It also took advantage of the differences in metabolic rates between cancer cells and healthy cells, detecting temperature differences upon heating from microwave energy. It was capable of locating tumors less than 1 cm in diameter. The system's transmitter produced 25 W at 1.6 GHz into a ridged waveguide in contact with the patient's body. The receiver, operating at 4.7 GHz, featured a GaAs FET amplifier with 1.8-dB noise figure and 65-dB gain.
By the mid-'80s, microwave energy had also been combined with surgical hardware to create the world's first microwave scapel (Fig. 2). Developed by researchers at the University of Maryland (College Park, MD), and marketed by Advanced Medical Imaging Corp. (Great Neck, NY), the microwave scapel had been patented in 1979 by Leonard Taylor of the Department of Electrical Engineering at the University of Maryland. The scapel integrated the effects of a localized S-band microwave field with a standard scapel blade to control bleeding. The human tissue absorbs the microwave energy to a depth of about 1 cm, causing coagulation. This control of bleeding assists when operating on sensitive organs, such as the spleen and liver.
More recently, Communications Power Corp. (Hauppauge, NY) developed a rack-mounted solid-state amplifier system for magnetic resonance imaging (MRI) applications in the fight for early detection of cancer tumors. The company's model 10.5T2000M-16/1C 32-kW amplifier system powers MRI scanners operating from 40 to 450 MHz, enabling them to achieve 10.5-T magnetic field strength to perform high-resolution, full-body MRI scans (see Microwaves & RF, March 2011, p. 98).