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Noninvasive intra-cardiac pressure estimation utilizing subharmonic aided pressure estimation (SHAPE)
Dissertation   Open access

Noninvasive intra-cardiac pressure estimation utilizing subharmonic aided pressure estimation (SHAPE)

Cara Marie Esposito
Doctor of Philosophy (Ph.D.), Drexel University
Jun 2020
DOI:
https://doi.org/10.17918/00000031
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Abstract

Echocardiography
Echocardiography utilizes ultrasound waves to examine functionality of the heart. The application of echocardiographic techniques for the assessment of cardiac function is limited due to the inability to measure intra-cardiac pressures. Pressure measurements within the chambers of the heart yield critical information for diagnosis and management of cardiovascular diseases. The current procedure used to measure intra-cardiac pressures, cardiac catheterization, is invasive and expensive. The American Heart Association's Heart Disease and Stroke Statistics 2020 Update reports that 116.4 million Americans (over the age of 20) suffer from high blood pressure, meaning these Americans may need to undergo a cardiac catheterization procedure to investigate the cause of their cardiac problems. The increased risk due to the invasiveness of the procedure and cost associated with this diagnostic procedure highlights the need for a noninvasive alternative. A possible solution to this problem is utilizing ultrasound contrast agents (UCAs) and subharmonic aided pressure estimation (SHAPE) to noninvasively estimate intra-cardiac pressures. Ultrasound contrast agents are gas-filled microspheres with a lipid, protein, or polymer shell that act as nonlinear oscillators, which yield energy components in the received echo signals at frequencies ranging from the subharmonic (half of transmit frequency) to higher harmonics and even ultraharmonics. The SHAPE technique relies on subharmonic signals from UCAs. Previous in vitro, pre-clinical, and clinical research performed by our group and others suggests that we can utilize SHAPE for estimating pressures. If the SHAPE technique can accurately measure intra-cardiac pressures (with errors < 5 mmHg between catheter and SHAPE pressures), then SHAPE will have a profound clinical impact by providing a noninvasive alternative to pressure measurements obtained during a cardiac catheterization procedure. The central hypothesis of this study is that real-time intra-cardiac pressures can be monitored and quantified noninvasively in humans using commercially available UCAs. This study aims to verify the use of subharmonic signals for intra-cardiac pressure estimation and to make this technology available as real-time implementation on a commercially available ultrasound scanner for clinical applications. This technique has potential to reduce the number of cardiac catheterizations performed and consequently, the associated risks and costs. Moreover, it will provide a technique for relatively frequent monitoring of intra-cardiac pressures. This will help with early diagnosis and frequent monitoring of cardiac disease, which will reduce the need for more invasive interventions.

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