Ph.D. Thesis Defense - Noninvasive Ambient Pressure Estimation using Ultrasound Contrast Agents: Invoking Subharmonics for Cardiac and Hepatic Applications
Date: July 13, 2012
Time: 9:00 AM
Location: Bossone Research Enterprise Center, Room: 709
Advisors: Peter A. Lewin, Ph.D., and Flemming Forsberg, Ph.D.
Ultrasound contrast agents (UCAs) are encapsulated microbubbles that provide a source for acoustic impedance mismatch with the blood, due to difference in compressibility between the gas contained within these microbubbles and the blood. When insonified by an ultrasound beam, these UCAs act as nonlinear scatterers and enhance the echoes of the incident pulse, resulting in scattering of the incident ultrasound beam and emission of fundamental (f0), subharmonic (f0/2), harmonic (n*f0; n∈ Ν) and ultraharmonic (((2n-1)/2)*f0; n∈ Ν & n > 1) components in the scattered beam profile.
A promising approach to monitor in vivo pressures revolves around the fact that the incident acoustic beam can be tailored to induce an ambient pressure dependent subharmonic signal. This technique is referred to as subharmonic aided pressure estimation or SHAPE. This project develops and evaluates the feasibility of SHAPE to noninvasively monitor cardiac and hepatic pressures (using commercially available ultrasound scanners and UCAs), because invasive catheter based pressure measurements are used currently for these applications.
In vitro results showed that the standard error between catheter pressures and SHAPE results is below 10 mmHg with a correlation coefficient value of above 0.9. In vivo results proved the feasibility of SHAPE to noninvasively estimate clinically relevant left and right ventricular (LV and RV) pressures. The maximum error in estimating the LV and RV systolic and diastolic pressures was 3.5 mmHg. The ability of SHAPE to identify induced portal hypertension (PH) was also proved. The changes in the SHAPE data correlated significantly (p < 0.05) with the changes in the PV pressures and the absolute amplitudes of the subharmonic signal also correlated with absolute PV pressures.
The SHAPE technique provides the ability to noninvasively obtain in vivo pressures. This technique is applicable not only for critically ill patients, but also for screening symptomatic patients and maybe for other clinical pressure monitoring applications, as well.
The Bossone Research Enterprise Center is located at the corner of 32nd and Market Streets.