Biomedical subjects
Publications and source records attributed to F M Charbonnier.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.
Depth resolution, a measure of the thinnest layer of tissue which will cast a detectable radiographic shadow, significantly limits visibility in conventional chest technique. Depth resolution, averaged over the chest area, improves with increasing kilovoltage, and thin, soft tissues can be seen more readily. The visibility of calcifications increases with kilovoltage in some areas of the chest and decreases in others, which is again explained by depth resolution. Densitometric data verify the mechanism involved: the latitude of the radiographic image matches that of the conventional film at high kilovoltages, so that more chest images are recorded at high contrast where visibility is best.
The physical designs of field-emission and conventional x-ray tubes are compared, and the physical and geometric source properties are translated into optical and resolution characteristics using modulation transfer functions calculated for idealized and practical sources and verified by star test pattern measurements. The field-emission design has several advantages: axial symmetry, circular shape, and a relatively favorable intensity distribution of the focal spot; in addition, the focal spot size is independent of the tube current. These advantages greatly enhance uniformity over the field of view and may increase resolution by a factor of 2 for a given nominal source size, thus largely ofsetting the greater physical size of present field-emission sources.
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A simplified method has been developed to determine peak current, transthoracic impedance, and delivered energy during a damped sinusoidal defibrillation pulse. The discharge waveform information is generated from sampling the peak discharge current through a current transformer and measuring the voltage stored on the energy storage capacitor. For a given defibrillator circuit a unique relationship exists between the peak discharge current IM and the unknown external impedance Rext presented to the defibrillator by the patient; hence, measurement of IM allows calculation of Rext. A microprocessor-controlled algorithm provides delivered energy information using known internal resistance, capacitance, and inductance parameters. The benefit of this method of delivered energy calculation is that the current and voltage waveforms need not be digitized and then integrated to provide the desired information. This method also keeps defibrillation circuitry ground isolated and simplifies operation through the high electromagnetic fields generated during the discharge. The delivered energy information, along with time, date, and other patient parameters, is documented automatically with an annotation strip-chart recorder.