Improved selection of optimal acoustic output power for subharmonic aided pressure estimation of portal hypertension

Subharmonic aided pressure estimation (SHAPE) is based on the inverse relationship between the subharmonic amplitude of contrast microbubbles and the ambient pressure. A noninvasive ultrasound based pressure estimation procedure would be a major development in the diagnosis of portal hypertension and less invasive than the current hepatic venous pressure gradient (HVPG) measurement. The hypothesis of this study was that portal vein pressures could be monitored and quantified noninvasively in humans using SHAPE. For maximum SHAPE sensitivity, the optimum acoustic power is currently selected using an algorithm, which collects subharmonic data at power levels increasing from 0 % to 100 % in 8 cine clips. The ROI is selected on a common Maximum Intensity Projection (MIP) for all these 8 clips, data is plotted against the power levels and the point of maximum inflection gives the optimum power. However, this algorithm is prone to motion due to breathing and can greatly affect the results, hence was improved to minimize the error.