Subharmonic contrast microbubble signals for noninvasive pressure estimation under static and dynamic flow conditions

Area of Science:

• Medical Ultrasound
• Biomedical Engineering
• Diagnostic Imaging

Background:

• Noninvasive blood pressure estimation remains a clinical challenge.
• Current methods may be invasive or lack precision.
• Microbubble-based ultrasound contrast agents offer novel signal properties.

Purpose of the Study:

• To introduce and validate the Subharmonic Aided Pressure Estimation (SHAPE) technique.
• To assess the efficacy of SHAPE for noninvasive hydrostatic blood pressure measurement.
• To identify optimal parameters and contrast agents for SHAPE.

Main Methods:

• An in vitro experimental system using two transducers was developed.
• Five ultrasound contrast agents were tested across varying pressures and acoustic parameters.
• Linear regression analysis identified optimal SHAPE parameters and the most sensitive agent (Sonazoid).
• SHAPE was implemented on a commercial ultrasound scanner (Logiq 9) and tested under dynamic conditions.

Main Results:

• Subharmonic amplitudes decreased significantly (9-14 dB) with increasing hydrostatic pressure, showing strong linear correlation (r=0.98).
• First and second harmonic amplitudes showed minimal change (~2 dB).
• Sonazoid demonstrated the highest sensitivity for subharmonic pressure estimation.
• Real-time SHAPE implementation on a commercial scanner showed good agreement with pressure-catheter measurements (r²=0.87).

Conclusions:

• Subharmonic ultrasound contrast signals are reliable indicators of hydrostatic pressure.
• Sonazoid is the most sensitive agent for SHAPE.
• Real-time SHAPE technology on commercial scanners holds potential for noninvasive cardiovascular pressure monitoring.