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Noninvasive Intracardiac Pressure Estimation Utilizing Subharmonic Aided Pressure Estimation (SHAPE)

Thursday, May 28, 2020

12:00 PM-2:00 PM

BIOMED PhD Thesis Defense

Noninvasive Intracardiac Pressure Estimation Utilizing Subharmonic Aided Pressure Estimation (SHAPE)

Cara Esposito, PhD Candidate
School of Biomedical Engineering, Science and Health Systems
Drexel University

Jaydev Dave, PhD
Associate Professor of Radiology
Sidney Kimmel Medical College
Thomas Jefferson University

Peter Lewin, PhD
Richard B. Beard Distinguished University Professor
School of Biomedical Engineering, Science and Health Systems
Drexel University

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 intracardiac 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 intracardiac pressures, cardiac catheterization, is invasive and expensive. The mean hospital charge is $57,494, for diagnostic and interventional treatment. The American Heart Association’s Heart Disease and Stroke Statistics 2018 Update reports that 113 million Americans (over the age of 18) suffer from high blood pressure and approximately 46% do not have their high blood pressure under control, meaning these Americans may need to undergo a cardiac catheterization procedure to investigate the cause of their cardiac problems. The increased risk 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 intracardiac pressures. Ultrasound contrast agents are gas filled microspheres with a lipid, protein, or polymer shell. These agents increase the backscattered ultrasound signal from blood by approximately 30 dB. They also act as nonlinear oscillators, which means the received echo signals from the UCAs contain 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 intracardiac pressures (with errors < 5 mmHg between catheter and SHAPE pressures), then SHAPE will have a profound clinical impact by providing a noninvasive alternative to cardiac catheterization procedure.

A pilot study in humans (involving 15 subjects) indicated the feasibility of utilizing the SHAPE technique to noninvasively measure intracardiac pressures. Errors between SHAPE and catheter, for the pilot study, were as low as 2.6 mmHg with a correlation of -0.9 at the optimum incident acoustic output (IAO) levels. At other IAO levels the correlation between SHAPE and catheter pressures was low (-0.3). Obtaining data at the optimal IAO level (which is required for SHAPE) was not possible for all patients in this study, due to a limited time-window available for data acquisition (during ongoing catheterization procedure) coupled with hardware and software limitations of the ultrasound scanner used in that study. Clearly, real-time determination of the optimum IAO level for each patient is needed in order to transition SHAPE into the clinic.

One approach to automatically determine optimum IAO for SHAPE has been suggested and implemented for pressures that are not varying cyclically (e.g., portal vein pressures, which remain relatively constant during a measurement interval). The SHAPE technique needs to be developed further for real-time intracardiac pressure estimations including real-time automatic optimum IAO determination across an entire cardiac cycle. The central hypothesis of this study is that real-time in vivo intracardiac pressures can be monitored and quantified noninvasively in humans using commercially available UCAs.

This study aims to verify the use of subharmonic signals for intracardiac pressure estimation and to make this technology available as real-time implementation on a commercially available ultrasound scanner for clinical applications. This technique has the 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 intracardiac pressures.

Contact Information

Natalia Broz

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