Ultrasonic interrogation of tissue vibrations in arterial and organ injuries: Preliminary in vivo results

Abstract

Soft tissues surrounding vascular injuries are known to vibrate at audible and palpable frequencies, producing bruits and thrills. We report the results of a feasibility study where Doppler ultrasound (US) was used to quantitatively estimate the tissue vibrations after induced trauma in an animal model. A software-programmable US system was used to acquire quadrature-demodulated ensembles of received US echoes bypassing clutter filtering and other conventional Doppler processing stages. The waveforms of tissue velocity surrounding the injury site were then estimated from the clutter data using autocorrelation and analyzed to determine vibration characteristics. Six New Zealand white rabbits and two juvenile pigs were used for the study. The femoral artery of the anesthetized animal was punctured with an 18-gauge needle to model a peripheral arterial trauma, and the liver was surgically exposed and incised to model organ trauma. Two types of oscillatory tissue motion were observed: “vibrations” with high frequency (>50 Hz) and low peak-peak amplitude (<1 μm) and “flutter” with low frequency (<50 Hz) and high peak-peak amplitude (>1 μm). Active bleeding in femoral artery punctures produced tissue vibrations at the frequency of 323 ± 214 Hz (mean ± standard deviation, pooled for both rabbits and pigs) and the amplitude of 0.24 ± 0.15 μm. Active bleeding in liver incisions produced vibrations at the frequency of 120 ± 47 Hz and the amplitude of 0.33 ± 0.25 μm. Flutter was observed in punctured arteries at the frequency of 28 ± 13 Hz the amplitude of 2.92 ± 1.75 μm, and in incised livers at the frequency of 26 ± 6 Hz and the amplitude of 1.53 ± 0.76 μm. In a punctured artery, the vibration frequency and phase of tissue surrounding the artery were highly correlated between neighboring locations in tissue (correlation coefficient = 0.98), and with the flow oscillations in the lumen (correlation coefficient = 0.96). This preliminary study indicates that tissue vibrations could provide additional physiologic information for detecting, localizing and monitoring internal bleeding using US. (E-mail: ssikdar@u.washington.edu)