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.