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27 June 1988 Frequency Modulated Pulse For Ultrasonic Imaging
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Ultrasonic diagnosis depends on the information obtained as a result of ultrasonic sonation (irradiation) of the patient. If the exposure is too low, useful information is not obtained; if it were to be too high, harm to the patient could result. Most diagnostic Ultrasound imaging systems use short microsecond pulses as a sonation source and construct the image from the back-scattered signal. There is now growing theoretical and experimental evidence to suggest that these microsecond pulses have temporal peak intensities high enough to produce free radicals through the mechanism of transient cavitation. Within the framework of short pulses, it is not possible to decrease the intensity without sacrificing signal to noise ratio. In this paper we propose the use of a new frequency modulated pulse to resolve the above dilemma. A bandwidth similar to that of a short pulse is maintained, but the total energy of the pulse is now spread over a longer duration with the result that the temporal peak intensity can be reduced significantly. For the purpose of theoretical simulation, we have modeled the back-scattered signal as a convolution of the tissue impulse response with the incident pulse. A necessary post-processing step of pulse compression required to regain the resolution is also outlined. While maintaining the resolution, increase in sensitivity (signal to noise) is demonstrated by a comparison with the response from a conventional short pulse. This increase in sensitivity can be used to reduce the temporal peak intensity of the pulse, thereby reducing the possible bio-effects. Experimental setup to acquire and process the data for imaging is also described.
© (1988) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Navalgund A. H. K. Rao, E. R. Ritenour, and R. E. Hendrick "Frequency Modulated Pulse For Ultrasonic Imaging", Proc. SPIE 0914, Medical Imaging II, (27 June 1988);

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