In vitro measurement of ambient pressure changes using a realistic clinical setup

Many attempts to find a non-invasive procedure to measure the local blood pressure have been made. In the last decade independent experiments have indicated that the amplitude of the subharmonic response from contrast agents is sensitive to the ambient pressure. This paper presents a new experimental setup for measuring the acoustic response of a contrast agent when subjected to ambient over pressure. The setup is very flexible offering completely arbitrary excitation and data acquisition, fast and accurate ambient pressure control, and precise timing. More importantly, it resembles a realistic clinical setup using a single array transducer for transmit and receive. In this experiment, the acoustic response of SonoVue (Bracco, Milano, Italy) was measured twice at six different ambient hydrostatic pressures in the interval 0 to 25 kPa with an accuracy within 0.5 kPa. The acquired RF data was filtered and beamformed before further processing. To compensate for variations in bubble response and to make the estimates more robust, the relation between the energy of the subharmonic and the fundamental component was chosen as a measure over the subharmonic peak amplitude. The results of the first measurement sequence show an ambient pressure sensitivity of 0.42 dB/kPa having a linear correlation coefficient of 0.94. In the second sequence, a sensitivity of 0.41 dB/kPa with a correlation coefficient of 0.89 was found.