ABSTRACT
We have investigated the possibility of building a singleband Dicke radiometer that is inexpensive, small-sized, stable, highly sensitive, and which consists of readily available microwave components. The selected frequency band is at 3.25-3.75 GHz which provides a reasonable compromise between spatial resolution (antenna size) and sensing depth for radiometry applications in lossy tissue. Foreseen applications of the instrument are non-invasive temperature monitoring for breast cancer detection and temperature monitoring during heating. We have found off-the-shelf microwave components that are sufficiently small (< 5 mm × 5 mm) and which offer satisfactory overall sensitivity. Two different Dicke radiometers have been realized: one is a conventional design with the Dicke switch at the front-end to select either the antenna or noise reference channels for amplification. The second design places a matched pair of low noise amplifiers in front of the Dicke switch to reduce system noise figure.Numerical simulations were performed to test the design concepts before building prototype PCB front-end layouts of the radiometer. Both designs provide an overall power gain of approximately 50 dB over a 500 MHz bandwidth centered at 3.5 GHz. No stability problems were observed despite using triple-cascaded amplifier configurations to boost the thermal signals. The prototypes were tested for sensitivity after calibration in two different water baths. Experiments showed superior sensitivity (36% higher) when implementing the low noise amplifier before the Dicke switch (close to the antenna) compared to the other design with the Dicke switch in front. Radiometer performance was also tested in a multilayered phantom during alternating heating and radiometric reading. Empirical tests showed that for the configuration with Dicke switch first, the switch had to be locked in the reference position during application of microwave heating to avoid damage to the active components (amplifiers and power meter). For the configuration with a low noise amplifier up front, damage would occur to the active components of the radiometer if used in presence of the microwave heating antenna. Nevertheless, this design showed significantly improved sensitivity of measured temperatures and merits further investigation to determine methods of protecting the radiometer for amplifier first front ends.
ABSTRACT
We have investigated the possibility of building a Dicke radiometer that is inexpensive, small-sized, stable, high sensitivity and consists of readily available microwave components. The selected frequency band is at 3-4 GHz and can be used for breast cancer detection, with sufficient spatial resolution. We have found microwave components that are small (< 5mm × 5 mm) and provide sufficient sensitivity. We have built two different Dicke radiometers: One is of conventional design with Dicke switch at front end to select antenna or noise rererence and the other with a low noise amplifier before the Dicke Switch. We have tested this concept with simulations and built prototypes. The two designs provide a gain of approximately 50 dB, and bandwidth of about 500 MHz. One of the designs has a stability µ > 1 and the other design provide instability µ < 1 for a part of the pass band. The prototypes are tested for sensitivity after calibration in two different known temperature waterbaths. The results show that the design with the low noise amplifier before the Dicke switch has 36% higher sensitivity than the other design with Dicke switch in front.
ABSTRACT
BACKGROUND: The purpose of this study was to assess to what extent symptoms and signs of bacterial infection are present and evaluated in patients admitted to the hospital for exacerbation of chronic obstructive pulmonary disease (COPD) in relation to initiation of antibiotic treatment. METHODS: All adult patients (>18 years of age) discharged from a department of internal medicine in Copenhagen in 1997 with a diagnosis of exacerbation of COPD were included in our study and their reports were retrospectively reviewed. Gender, age, number of admissions and length of hospital stay, use of antibiotics and steroids prior to admission, temperature, white blood cell (WBC) count, results of lung auscultation and X-ray examination of the thorax at admittance, and growth of sputum culture and antibiotic treatment in the hospital were all registered. RESULTS: A total of 400 admissions took place. In 104 of them, chest X-ray was compatible with pneumonia, and 99 cases were treated with antibiotics. In 44% of the remaining 296 cases, antibiotics were given. It was found that 25-45% of the patients with very little evidence of infection-i.e. the absence of, or only the presence of, one of the following indicators of infection: fever (temperature>37.5 degrees C), a raised WBC count (>9 billion/l), or crepitation at lung auscultation-were given antibiotics. In cases presenting with two or three of these indicators, 50-75% were given antibiotics. In 85% of the cases, penicillin or a macrolide was the initial antibiotic of choice. The median hospital stay was 6 days for the entire group of patients. CONCLUSION: These data suggest that, in patients with acute exacerbation of COPD, a relatively high number of patients with only weak symptoms or signs of bacterial infection are treated with antibiotics.
