The theory on microbubbles clearly indicates a relation between the ambient pressure and the acoustic behavior
of the bubble. The purpose of this study was to optimize the sensitivity of ambient pressure measurements,
using the subharmonic component, through microbubble response simulations. The behaviour of two different
contrast agents was investigated as a function of driving pulse and ambient overpressure, <i>p<sub>ov</sub></i>. Simulations of
Levovist using a rectangular driving pulse show an almost linear reduction in the subharmonic component as
<i>p<sub>ov</sub></i> is increased. For a 20 cycles driving pulse, a reduction of 4.6 dB is observed when changing <i>p<sub>ov</sub></i> from 0 to
25 kPa. Increasing the pulse duration makes the reduction even more clear. For a pulse with 64 cycles, the
reduction is 9.9 dB. This simulation is in good correspondence with measurement results presented by Shi et al.
1999, who found a linear reduction of 9.6 dB. Further simulations of Levovist show that also the shape and the
acoustic pressure of the driving pulse are very important factors. The best pressure sensitivity of Levovist was
found to be 0.88 dB/kPa. For Sonazoid, a sensitivity of 0.71 dB/kPa has been found, although the reduction is
not completely linear as a function of the ambient pressure.