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Effects of encapsulation damping on the excitation threshold for subharmonic generation from contrast microbubbles.

ABSTRACT: A recent study [Katiyar and Sarkar (2011). J. Acoust. Soc. Am. 130, 3137-3147] showed that in contrast to the analytical result for free bubbles, the minimum threshold for subharmonic generation for contrast microbubbles does not necessarily occur at twice the resonance frequency. Here increased damping-either due to the small radius or the encapsulation-is shown to shift the minimum threshold away from twice the resonance frequency. Free bubbles as well as four models of the contrast agent encapsulation are investigated varying the surface dilatational viscosity. Encapsulation properties are determined using measured attenuation data for a commercial contrast agent. For sufficiently small damping, models predict two minima for the threshold curve-one at twice the resonance frequency being lower than the other at resonance frequency-in accord with the classical analytical result. However, increased damping damps the bubble response more at twice the resonance than at resonance, leading to a flattening of the threshold curve and a gradual shift of the absolute minimum from twice the resonance frequency toward the resonance frequency. The deviation from the classical result stems from the fact that the perturbation analysis employed to obtain it assumes small damping, not always applicable for contrast microbubbles.

SUBMITTER: Katiyar A

PROVIDER: S-EPMC3505217 | biostudies-other | 2012 Nov

REPOSITORIES: biostudies-other

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Project description:Purpose To investigate if the right ventricular (RV) systolic and left ventricular (LV) diastolic pressures can be obtained noninvasively using the subharmonic-aided pressure estimation (SHAPE) technique with Sonazoid microbubbles. Materials and Methods Individuals scheduled for a left and/or right heart catheterization were prospectively enrolled in this institutional review board-approved clinical trial from 2017 to 2020. A standard-of-care catheterization procedure was performed by advancing fluid-filled pressure catheters into the LV and aorta (n = 25) or RV (n = 22), and solid-state high-fidelity pressure catheters into the LV and aorta in a subset of participants (n = 18). Study participants received an infusion of Sonazoid microbubbles (GE HealthCare), and SHAPE data were acquired using a validated interface developed on a SonixTablet (BK Medical) US scanner, synchronously with the pressure catheter data. A conversion factor, derived using cuff-based pressure measurements with a SphygmoCor XCEL PWA (ATCOR) and subharmonic signal from the aorta, was used to convert the subharmonic signal into pressure values. Errors between the pressure measurements obtained using the SHAPE technique and pressure catheter were compared. Results The mean errors in pressure measurements obtained with the SHAPE technique relative to those of the fluid-filled pressure catheter were 1.6 mm Hg ± 1.5 [SD] (P = .85), 8.4 mm Hg ± 6.2 (P = .04), and 7.4 mm Hg ± 5.7 (P = .09) for RV systolic, LV minimum diastolic, and LV end-diastolic pressures, respectively. Relative to the measurements with the solid-state high-fidelity pressure catheter, the mean errors in LV minimum diastolic and LV end-diastolic pressures were 7.2 mm Hg ± 4.5 and 6.8 mm Hg ± 3.3 (P ≥ .44), respectively. Conclusion These results indicate that SHAPE with Sonazoid may have the potential to provide clinically relevant RV systolic and LV diastolic pressures. Keywords: Ultrasound-Contrast, Cardiac, Aorta, Left Ventricle, Right Ventricle ClinicalTrials.gov registration no.: NCT03245255 © RSNA, 2024.

Project description:Background The current standard for assessing the severity of portal hypertension is the invasive acquisition of hepatic venous pressure gradient (HVPG). A noninvasive US-based technique called subharmonic-aided pressure estimation (SHAPE) could reduce risk and enable routine acquisition of these pressure estimates. Purpose To compare quantitative SHAPE to HVPG measurements to diagnose portal hypertension in participants undergoing a transjugular liver biopsy. Materials and Methods This was a prospective cross-sectional trial conducted at two hospitals between April 2015 and March 2019 (ClinicalTrials.gov identifier, NCT02489045). This trial enrolled participants who were scheduled for transjugular liver biopsy. After standard-of-care transjugular liver biopsy and HVPG pressure measurements, participants received an infusion of a US contrast agent and saline. During infusion, SHAPE data were collected from a portal vein and a hepatic vein, and the difference was compared with HVPG measurements. Correlations between data sets were determined by using the Pearson correlation coefficient, and statistical significance between groups was determined by using the Student t test. Receiver operating characteristic analysis was performed to determine the sensitivity and specificity of SHAPE. Results A total of 125 participants (mean age ± standard deviation, 59 years ± 12; 80 men) with complete data were included. Participants at increased risk for variceal hemorrhage (HVPG ≥12 mm Hg) had a higher mean SHAPE gradient compared with participants with lower HVPGs (0.79 dB ± 2.53 vs -4.95 dB ± 3.44; P < .001), which is equivalent to a sensitivity of 90% (13 of 14; 95% CI: 88, 94) and a specificity of 80% (79 of 99; 95% CI: 76, 84). The SHAPE gradient between the portal and hepatic veins was in good overall agreement with the HVPG measurements (r = 0.68). Conclusion Subharmonic-aided pressure estimation is an accurate noninvasive technique for detecting clinically significant portal hypertension. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Kiessling in this issue.

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Effects of encapsulation damping on the excitation threshold for subharmonic generation from contrast microbubbles.

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