Pulse inversion Doppler: a new method for detecting nonlinearechoes from microbubble contrast agents

摘要

A novel technique for the selective detection of ultrasoundncontrast agents, called pulse inversion Doppler, has been developed. Innthis technique, a conventional Doppler or color Doppler pulse sequencenis modified by inverting every second transmit pulse. Eithernconventional or harmonic Doppler processing is then performed on thenreceived echoes. In the resulting Doppler spectra, Doppler shifts fromnlinear and nonlinear scattering are separated into two distinct regionsnthat can be analyzed separately or combined to estimate the ratio ofnnonlinear to linear scattering from a region of tissue. The maximumnDoppler shift that can be detected is 1/2 the normal Nyquist limit. Thisnhas the advantage over conventional harmonic Doppler that it cannfunction over the entire bandwidth of the echo signal, thus achievingnsuperior spatial resolution in the Doppler image. In vitro measurementsncomparing flowing agent and cellulose particles suggest that pulseninversion Doppler can provide 3 to 10 dB more agent to tissue contrastnthan harmonic imaging with similar pulses. Similar measurements suggestnthat broadband pulse inversion Doppler can provide up to 16 dB morencontrast than broadband conventional Doppler. Nonlinear propagationneffects limit the maximum contrast obtainable with both harmonic andnpulse inversion Doppler techniques