A comparative evaluation of two subharmonic-aided pressure estimation (SHAPE) analysis methods

Pressure measurement in clinical practice is a valuable tool for diagnostic evaluation, especially in diseases such as portal hypertension. Currently, portal pressures are measured by invasive hepatic vein catheterization, posing risks to patients, and limiting how often measurements can be obtained. Subharmonic-aided pressure estimation (SHAPE) is an ultrasound-based technique that leverages ultrasound contrast agents (UCAs) to estimate changes in hydrostatic pressure. UCAs act as nonlinear oscillators when exposed to high enough acoustic pressures (typically > 200 kPa) and produce significant energy components ranging from subharmonics to higher harmonics. Tissues do not generate significant subharmonic components, thus making it the optimal component for SHAPE. SHAPE is performed using subharmonic imaging complimented by an acoustic pressure optimization algorithm to induce the highest sensitivity to hydrostatic pressure in the UCAs. Traditionally, multiple acquisitions of contrast clips are used to identify the subharmonic amplitude and calculate SHAPE parameters, but recently, a faster method of SHAPE has been proposed, utilizing only the acoustic pressure optimization algorithm to obtain subharmonic amplitudes. The objective of this work is to compare the two methods, SHAPE and fast-SHAPE, in the same patients, to explore the utility of fast-SHAPE.