Parametric study of peak negative pressure distribution and its relationship to bubble destruction

Imaging based on bubble destruction is used to detect contrast agents. Since the origin of bubble destruction is still poorly understood, the authors investigated the distribution and potential role of peak negative pressure (PNP). Firstly, PNP distribution for a phased array was simulated. The influence of central frequency and bandwidth, focus and number of crystals was investigated. Secondly, the PNP for a clinical scanner was measured using a hydrophone. Thirdly, bubble destruction was investigated using a phantom containing a contrast medium. Simulations showed that PNPs and their homogenicity within the sector scan increased with decreasing frequency, almost independent of the bandwidth. Increasing the focal depth decreased overall PNP but maximal PNP remained approximately at the same depth, PNP was not necessarily directly related to the distance from the transducer: at the same distance it was higher in the lateral scanlines (depending on focus depth). Hydrophone measurements showed a PNP distribution similar to the simulation. The phantom suggested that bubble destruction is related to PNP and shows a similar inhomogeneity in the scan plane. Since the PNP distribution and resulting bubble destruction is inhomogeneous, quantitative contrast imaging based on bubble destruction will have to take this spatial variation into account