Effect of Pulse Shaping on Subharmonic Aided Pressure Estimation In Vitro and In Vivo

Abstract

Subharmonic imaging (SHI) is a technique that uses the nonlinear oscillations of microbubbles when exposed to ultrasound at high pressures transmitting at the fundamental frequency i.e., fo and receiving at half the transmit frequency i.e., fo/2. Subharmonic aided pressure estimation (SHAPE) is based on the inverse relationship between the subharmonic amplitude of the microbubbles and the ambient pressure change. Eight waveforms with different envelopes were optimized with respect to acoustic power at which the SHAPE study is most sensitive. The study was run with four input transmit cycles, first in vitro and then in vivo in three canines to select the waveform that achieved the best sensitivity for detecting changes in portal pressures using SHAPE. A Logiq 9 scanner with a 4C curvi-linear array was used to acquire 2.5 MHz radio-frequency data. Scanning was performed in dual imaging mode with B-mode imaging at 4 MHz and a SHI contrast mode transmitting at 2.5 MHz and receiving at 1.25 MHz. Sonazoid, which is a lipid stabilized gas filled bubble of perfluorobutane, was used as the contrast agent in this study. A linear decrease in subharmonic amplitude with increased pressure was observed for all waveforms (r from −0.77 to −0.93; p<0.001) in vitro. There was a significantly higher correlation of the SHAPE gradient with changing pressures for the broadband pulses as compared to the narrowband pulses in both in vitro and in vivo results. The highest correlation was achieved with a Gaussian windowed binomial filtered square wave with an r-value of −0.95. One of the 3 canines was eliminated for technical reasons, while the other 2 produced very similar results to those obtained in vitro (r from −0.72 to −0.98; p<0.01). The most consistent in vivo results were achieved with the Gaussian windowed binomial filtered square wave (r = −0.95 and −0.96). In conclusion, using this waveform is an improvement to the existing SHAPE technique (where a square wave was used) and should make SHAPE more sensitive for noninvasively determining portal hypertension.

Effect of Temperature on the Size Distribution, Shell Properties, and Stability of Definity®

“…Shell properties influence the threshold for producing nonlinear bubble activity. Imaging techniques based on the nonlinear response of UCAs are under development to visualize vasculature (Maresca et al 2013; Shekhar et al 2016b) and for pressure sensing (Gupta et al 2017). These experiments are often reported at room temperature, which may influence the interpretation of this data for clinical translation.…”

Improvement of Detection Sensitivity of Microbubbles as Sensors to Detect Ambient Pressure

“…Based on the above results, the technique called the subharmonic-aided pressure estimation (SHAPE) for noninvasive blood pressure estimation was proposed and proven in the animal and human experiments [19,31,32,33]. For animal experiments, the results from the SHAPE method were consistent with the data from catheter, with <2.5 mmHg pressure errors [19].…”

Primary prevention of bleeding from esophageal varices in patients with liver cirrhosis: An update and review of the literature

“…Also, patients with a damping index (minimum velocity/maximum velocity of the hepatic vein waveform) of >0.6 are significantly more likely to have HVPG > 12 mmHg 18 . The subharmonic‐aided pressure estimation of the hepatic vein could be useful to suspect PH 19 . The subharmonic‐aided pressure estimation gradient and HVPG values had a linear correlation of .82 and even .97 for patients with an HVPG > 12 mmHg 20 .…”