Alan H. Barrett

Microwave Thermography: Principles, Methods and Clinical Applications*

We review the physical principles, method of operation, measurement limitations, and potential medical applications of microwave thermography. We present detailed results of a study of breast cancer detection at 1.3 and 3.3 GHz, including the dependence of detection rates on microwave frequency, time, tumor depth, and tumor size. At 1.3 GHz, microwave thermography detects breast cancer as well as infrared thermography (true-positive rate = 0.76 when true-negative rate = 0.63). When the two methods are combined, the true-positive rate increases by about 0.1 over that of either method alone.

Microwave Spectrometer on the Nimbus 5 Satellite: Meteorological and Geophysical Data

The Nimbus 5 microwave spectrometer has been used to measure thermal radiation in five frequency bands between 22.235 and 58.8 gigahertz, and has yielded both the temperature profile and, over ocean, the vapor and liquid water content of the terrestrial atmosphere, even in overcast conditions. Information has also been obtained on geophysical parameters that affect the surface emissivity, such as ice type, sea roughness, and snow cover. The experiment demonstrates the considerable potential of passive microwave sensing of meteorological and geophysical parameters.

Discovery of Hydroxyl Radio Emission from Infrared Stars

Radio spectral line emission from hydroxyl radicals has been detected from four infrared stars. The emission from the infrared star NML Cygni at 1612 megahertz is the strongest radio emission line yet detected. Sixteen other stars with infrared excesses showed no detectable hydroxyl radio emission.

DETECTION OF METHYL ALCOHOL IN ORION AT A WAVELENGTH OF approximately 1 CENTIMETER.

Methyl alcohol transitions in Orion at 1 cm noting emission source coincidence with IR nebula

The formation of elephant-trunk globules in the Rosette nebula: CO observations

The prominent elephant-trunk globules in the northwest quadrant of the Rosette nebula have been observed in the microwave lines of CO and /sup 13/CO (J=1..-->..0). The CO emission closely follows the optical outline of the obscuring material and leaves little doubt that the emission is associated with the globules. The physical characteristics derived are typical of those observed in other dust globules which are not necessarily associated with H II regions.

Spectral Line Interferometry with Independent Time Standards at Stations Separated by 845 Kilometers

An upper limit of 0.02 second of arc has been determined for a hydroxyl radical (OH) emission region associated with the radio source W3, with the use of a Michelson interferometer consisting of two radio telescopes 845 kilometers apart. Timing was provided at the stations by independent atomic frequency standards. The 1665-megahertz radiation was translated to video frequency and recorded digitally on magnetic tapes which were later processed by computer, yielding fringe phase and amplitude as a function of frequency over the received bandwidth.

MICROWAVE THERMOGRAPHY OF NORMAL AND CANCEROUS BREAST TISSUE

In this report we review the relevant physical principles and instrumentation of centimeter wavelength microwave radiometry. We have called this technique microwave thermography in analogy with the well-known infrared method. We present results of a clinical study of breast cancer detection at 1.3 GHz (23-cm wavelength) and 3.3 GHz (9-cm), and we describe the performance of our new 6-GHz (5-cm) radiometer. Some of this material has been presented elsewherel-’’ and is included here for purposes of review.

The structure of the OH source in W3.

Interferometric study of OH emission source in W3 /IC 1795/ region, processing data on digital computer

OH RADIO EMISSION ASSOCIATED WITH INFRARED STARS.

OH radio emission from IR stars, discussing spectra, polarization properties and red giant star model with expanding atmosphere

Water Vapor: Observations of Galactic Sources

We measured the emission of water vapor at a wavelength of 1.35 centimeters from nine sources with the 120-foot (36.5-meter) Haystack antenna. Eight sources lie within 30 seconds of arc of the hydroxyl sources of 18 centimeters but not all hydroxyl sources produced detectable emission of water vapor. All sources are smaller than 30 seconds of arc in angular diameter, but we resolved at least three separate sources in the Orion Nebula. We do not find that the known hyperfine components are present with the equilibrium intensity distribution.