Frequency-dependent attenuation of ultrasonic pulses by soft tissues leads to a shift of the frequency content of the pulse toward lower frequencies. The sensitivity of a single transducer, pulse-echo imaging system is effected by this shift; it is reduced because the frequency content of the ultrasonic pulses returned to the transducer is shifted below the frequency range to which the transducer is most sensitive. This shift in frequency is in the simplest case dependent upon the bandwidth of frequencies transmitted into the tissues and dependent upon both the attenuation coefficient of the tissue and the total distance over which the pulse travels. The sensitivity of such an imaging system will be higher than the corresponding single transducer system; this approach proffers a way of significantly reducing the exposure of patients to ultrasonic energy. It is estimated that sensitivity of a representative system using a 3.4 MHz transducer with a 1.26 MHz bandwidth can be improved by a factor of approximately 10 by using a 1.2 MHz receiving transducer in conjunction with the 3.4 MHz transducer. This is translated into a reduction in accoustic power and, consequentially, in exposure by a factor of approximately 100. The purpose of the research proposal is to reduce patient exposure during ultrasonic scanning procedures for most types of imaging systems without affecting diagnostic efficacy of the ultrasonograms.
NIH ExPorter
NIH ExPorter