SHAPE for ICP Assessment

Plain-language summary

The Subharmonic Aided Pressure Estimation (SHAPE) technique is a noninvasive ultrasound-based imaging technique that can estimate ambient pressure using subharmonic emissions from ultrasound contrast agents. Ultrasound contrast agents are encapsulated microbubbles (mean diameter \< 8 µm) with a lipid, protein, or polymer shell that traverse the entire vasculature. When the contrast microbubbles are insonated with relatively high acoustic pressures (\>100-150 kPa), these microbubbles act as nonlinear oscillators yielding energy components in the received echo signals at frequencies ranging from the subharmonic (half of transmit frequency) to higher harmonics and even ultraharmonics. Based on empirical evidence, the subharmonic signal exhibits a sigmoidal relationship with incident acoustic pressure i.e., subharmonic signal can be divided into occurrence, growth and saturation stages. In the growth stage, the subharmonic signal has shown sensitivity to ambient pressure characterized by an inverse linear relationship between subharmonic signal and ambient pressure changes. This inverse linear relationship forms the basis for the SHAPE technique. Several pre-clinical and clinical studies have been conducted to utilize the SHAPE technique for in vivo pressure estimation e.g., to diagnose portal hypertension, to estimate intra-cardiac pressures and to determine interstitial fluid pressures. The core imaging mode underpinning the SHAPE technology (subharmonic imaging) is now available on some commercial scanners. In the proposed pilot study, the SHAPE technique will be leveraged for monitoring intracranial pressure (ICP). The use of SHAPE technique for the ophthalmic artery could potentially provide an accurate noninvasive method of measuring ICP in patients with idiopathic intracranial hypertension (IIH) and other conditions of raised ICP, which would revolutionize the field.

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