Pressure dependence of subharmonic signals from contrast microbubbles

Noninvasive pressure estimation in heart cavities and in major vessels woul d provide clinicians with a valuable tool for assessing patients with heart and vascular diseases. Some microbubble-based ultrasound contrast agents a re particularly well suited for pressure measurements because their substan tial compressibility enables microbubbles to vary significantly in size in response to changes in pressure. Pressure changes should then affect reflec tivity of microbubbles after intravenous injection of a contrast agent. Thi s has been demonstrated with a galactose-based contrast agent using 2.0-MHz ultrasound tone bursts. Preliminary results indicate that, over the pressu re range of 0-186 mmHg, the subharmonic amplitude of scattered signals decr eases by as much as 10 dB under optimal acoustic settings and the first and second harmonic amplitudes decrease by less than 3 dB, An excellent correl ation between the subharmonic amplitude and the hydrostatic pressure sugges ts that the subharmonic signal may be utilized for noninvasive detection of pressure changes. (C) 1999 World Federation for Ultrasound in Medicine & B iology.