Frequency modulated pulse for ultrasonic imaging in an attenuating medium

Rao, Navalgund, "Frequency modulated pulse for ultrasonic imaging in an attenuating medium" (1990). IEEE,Accessed from ABSTRACT There is now increasing theoretical and experimental evidence that ultrasound used at intensities employed clinically, can produce effects characteristic of transient cavitation. Probability to cause bioeffects by transient cavitation is immensely greater above a threshold peak intensity of the interrogating ultrasound pulse. Within the framework of short pulses used in diagnostics, 1 is not possible to reduce the peak intensity without sacrificing signal to noise ratio. We have been investigating the usefulness of a frequency modulated interrogating pulse to resolve the above dilemma. Simulations and experiments in non attenuating medium show that a factor of 16 to 50 reduction in peak intensity is possible without sacrificing the signal primarily used for imaging or the resolution. This factor depends on the effective time-bandwidth product of the frequency modulated pulse. However, in a frequency dependent attenuating medium, such as sofl tissue, this advantage could diminish. We have incorporated a linear in frequency and linear phase model for attenuation in our simulation process. Time-band width product is evaluated for reflectors at various depths and also as a function of center frequency and bandwidth of the frequency modulated pulse.