Effects of Pressure Cycling, Concentration, and Excitation Amplitude on Ambient Pressure Sensitivity of...

The high ambient pressure sensitivity of the subharmonic response from contrast microbubbles makes it a promising means for noninvasive diagnosis of vascular pressures, i.e., subharmonic aided pressure estimation (SHAPE). Here, we investigated the effects of concentration and multiple pressure cycles on the subharmonic response of Sonazoid, a commercially available microbubble with a perfluorobutane gas core.

We performed a pressure sensitivity study at 3 MHz excitation frequency, 100-700 kPa peak negative pressures (PNP), and ambient overpressures of 10-20 kPa (75-150 mm Hg) using three different microbubble concentrations (0.05 mL/L, 0.125 mL/L, and 0.5 mL/L).

At lower PNPs (100-300 kPa), only the highest concentration showed a subharmonic signal, with a negative correlation with ambient pressure in the first pressure cycle and a positive one in the following cycles. Meanwhile, for higher PNPs (>300 kPa), there was very little subharmonic for the highest concentration, and the pressure sensitivity progressively decreased with increasing microbubble concentration. For higher PNPs, the subharmonic response showed a negative correlation with overpressure. SHAPE calibrations were also provided for overpressures between 0 and 20 kPa (0-150 mm Hg) at each concentration.

The findings offer new insights into the pressure sensitivity of Sonazoid microbubbles and might help optimize SHAPE performance in clinical studies.