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In this study we present a design for a multi-frequency microwave radiometer aimed at prolonged monitoring of deep brain temperature in newborn infants and suitable for use during hypothermic neural rescue therapy. We identify appropriate hardware to measure brightness temperature and evaluate the accuracy of the measurements. We describe a method to estimate the tissue temperature distribution from measured brightness temperatures which uses the results of numerical simulations of the tissue temperature as well as the propagation of the microwaves in a realistic detailed three-dimensional infant head model. The temperature retrieval method is then used to evaluate how the statistical fluctuations in the measured brightness temperatures limit the confidence interval for the estimated temperature: for an 18 degrees C temperature differential between cooled surface and deep brain we found a standard error in the estimated central brain temperature of 0.75 degrees C. Evaluation of the systematic errors arising from inaccuracies in model parameters showed that realistic deviations in tissue parameters have little impact compared to uncertainty in the thickness of the bolus between the receiving antenna and the infant's head or in the skull thickness. This highlights the need to pay particular attention to these latter parameters in future practical implementation of the technique.

[1] Clinical trials of hypothermic brain treatment for newborn babies are currently hindered by the difficulty in measuring deep brain temperatures. As one of the possible methods for noninvasive and continuous temperature monitoring that is completely passive and inherently safe is passive microwave radiometry (MWR). We have developed a five-band microwave radiometer system with a single dual-polarized, rectangular waveguide antenna operating within the 1–4 GHz range and a method for retrieving the temperature profile from five radiometric brightness temperatures. This paper addresses (1) the temperature calibration for five microwave receivers, (2) the measurement experiment using a phantom model that mimics the temperature profile in a newborn baby, and (3) the feasibility for noninvasive monitoring of deep brain temperatures. Temperature resolutions were 0.103, 0.129, 0.138, 0.105 and 0.111 K for 1.2, 1.65, 2.3, 3.0 and 3.6 GHz receivers, respectively. The precision of temperature estimation (2σ confidence interval) was about 0.7°C at a 5-cm depth from the phantom surface. Accuracy, which is the difference between the estimated temperature using this system and the measured temperature by a thermocouple at a depth of 5 cm, was about 2°C. The current result is not satisfactory for clinical application because the clinical requirement for accuracy must be better than 1°C for both precision and accuracy at a depth of 5 cm. Since a couple of possible causes for this inaccuracy have been identified, we believe that the system can take a step closer to the clinical application of MWR for hypothermic rescue treatment.

A method of retrieving a temperature-depth profile in biological object from a set of multi-frequency microwave radiometric data has been developed. The method is a combination of model-fitting and Monte Carlo techniques and is capable of estimating a profile and its confidence interval as a function of the depth. We use 2σ -intervals as a measure of the precision of tissue temperature measurements. The method was tested and supported by an experiment in which temperature distributions in a muscle equivalent agar phantom were measured using a 5-band, 1-3.8 GHz radiometer with the brightness temperature resolution of 0.05-0.07 K. A typical result of the experiment showed that 2σ -intervals were 1 K or less for 0 < z < 3 cm, 1.4 K at z = 4 cm, and 3 K at z = 5 cm. A numerical simulation study was made using this technique to assess effects of the selection of measurement frequencies, number of frequency bands, brightness temperature resolution of radiometer and thickness of fat layer on the precision. Resul...

An experimental three-band (1.5,2.5,3.5+-0.5GHz) radiometer system and a data analysis procedure have been developed for noninvasive measurement of the temperature at various depths in a biological body. Using them, we made temperature measurement experiments on the abdominal region of rabbits. The results of the experiments demonstrate the feasibility of the multifrequency radiometry for this purpose.

An assessment is made of the degradation that is caused by a water-filled bolus in the precision of tissue temperature measured noninvasively by a five-band microwave radiometry scheme. The precision is expressed in terms of the confidence interval of tissue temperature estimated from a set of five brightness temperatures measured with an experimental instrument operating at center frequencies of 1.2, 1.8, 2.5, 2.9, and 3.6 GHz, with a 0.4-GHz bandwidth. Results show that degradation due to a bolus having a thickness of about 1 cm is small when it is filled with deionized or distilled water. It is concluded that the use of water-filled bolus is permissible for microwave radiometric measurement. This is of a practical importance when the technique is used in combination with electromagnetic heating for hyperthermic treatment of cancer. >

Carbon fibers with fibrin glue were used as electrodes for diaphragm pacing. The electrodes were applied to three mongrel dogs and the effectiveness was tested. The carbon leads were glued to phrenic nerves by means of the fibrinogen and thrombin bilaterally. The tidal volumes and threshold current level for stimulation were measured at various time up to 9 weeks after implantation. Effective contraction of diaphragm were observed for 9 weeks. By using this electrode, the exfoliation of the nerve is not necessary, the nerve can be maintained in an intact state, and the risk of the implanting operation can be minimized.

A method was developed to grow homogeneous (Ga,Al)P alloy using a temperatue difference liquid phase epitaxial growth technique. In this method (Ga,Al)P polycrystals were prepared at 1000 °C prior to the growth of (Ga,Al)P alloy at 800 °C, which acted as the Al source to maintain the alloy composition constant during the growth. Electron probe microanalysis showed that the grown alloy was uniform within 0.01 mole fraction. It was also possible to control the alloy composition by this growth technique. Measurements of photoluminescence of the grown layer and electroluminescence of Zn‐diffused diode revealed the grown alloy was of high quality. Observed edge emission energy indicated that the band gap varied with alloy composition. The edge band emission spectra with fine structure were observed at 77 K.

A large waveguide applicator is proposed for deep regional hyperthermia, where a part of a patient's body is exposed to the TE/sub 10/ -mode waves in the rectangular waveguide through the holes made to fit the body cross section in the broad walls. The electric field and the specific absorption rate distribution produced by the applicator in a realistic model of a human body cross section calculated by a two-dimensional (2-D) numerical method are given.

GaP LPE layers were successfully grown from indium solvent. The lowest temperature at which a smooth layer was obtained was 580° C. The background carrier concentrations of the undoped layers grown at temperatures below 670° C were 1−6 × 10 15 cm -3 . It was found that this low background value was not due to the high level compensation. Low temperature growth is found to be effective to obtain high purity GaP crystals.

A reduction in dislocation density, typically by a factor of 3–8, was observed across the interface between LEC GaP (111)B substrate and an n‐type In‐doped GaP layer grown from indium solvent by liquid‐phase epitaxy. Doping of the epitaxial layer with indium contributed to the reduction in dislocation density in the epitaxial layer.

High‐quality GaP layers were obtained by liquid phase epitaxy at a low temperature, 650 °C, from indium solvent. We attribute the high quality of the LPE layers to the reduction in the concentrations of vacancies and unintentional impurities such as Si which would come from the growth system.