Abstract
Microbubbles are considered a promising tool for noninvasive estimation of local blood pressure. It is reported that the subharmonic scattering amplitude of microbubbles decreases by 9 to 12 dB when immersed in the media under an ambient pressure variation from 0 to 180 mmHg. However, the pressure sensitivity still needs to be improved to satisfy clinical diagnostic requirements. Here, we investigated the effects of acoustic parameters on the pressure sensitivity of microbubbles through measuring the acoustic attenuation and scattering properties of commercially available SonoVue microbubbles. Our results showed that the first harmonic, subharmonic, and ultraharmonic amplitudes of microbubbles were reduced by 6.6 dB, 10.9 dB, and 9.3 dB at 0.225 mechanical index (MI), 4.6 dB, 19.8 dB, and 12.3 dB at 0.25 MI, and 18.5 dB, 17.6 dB, and 12.6 dB at 0.3 MI, respectively, when the ambient pressure increased from 0 to 180 mmHg. Our finding revealed that a moderate MI (0.25–0.4) exciting microbubbles could significantly improve their sensitivities to detect ambient pressure.
Highlights
Measuring hydrostatic pressures in heart cavities and major vessels would provide clinicians with important information for evaluating valvular heart disease, congestive heart failure, portal and pulmonary hypertension, and various vascular diseases [1]
We experimentally demonstrated that the ambient pressure sensitivities of first harmonic (f ), subharmonic (1/2f ) and ultraharmonic (3/2f ) amplitudes from microbubbles could be improved significantly by tuning the p mechanical index (MI = PA / f ) defined as the ratio of the acoustic pressure PA (MPa) to the square root of the driving frequency f (MHz)
The results indicated that ultrasound contrast agent (UCA) injection time had a significant effect on its resonance frequency was decreased from 2.7 MHz to 1.82 MHz
Summary
Measuring hydrostatic pressures in heart cavities and major vessels would provide clinicians with important information for evaluating valvular heart disease, congestive heart failure, portal and pulmonary hypertension, and various vascular diseases [1]. Conventional clinical local blood pressure measurement is invasive through inserting one or several pressure catheters into heart cavities and large blood vessels to obtain the blood pressure, occasionally resulting in increased pain and infection risk for the patients [2]. The inserted plastic tube can change the hemodynamics of the surrounding medium, leading to an inaccurate measurement of blood pressure [3]. The ultrasound contrast agent (UCA) microbubble-based sensor is a promising noninvasive approach for blood pressure measurements [4]. Changes in the local blood pressure can lead to variation in the acoustic characteristics of microbubbles
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