Dataset Information

Excitation threshold for subharmonic generation from contrast microbubbles.

ABSTRACT: Six models of contrast microbubbles are investigated to determine the excitation threshold for subharmonic generation. The models are applied to a commercial contrast agent; its characteristic parameters according to each model are determined using experimentally measured ultrasound attenuation. In contrast to the classical perturbative result, the minimum threshold for subharmonic generation is not always predicted at excitation with twice the resonance frequency; instead it occurs over a range of frequencies from resonance to twice the resonance frequency. The quantitative variation of the threshold with frequency depends on the model and the bubble radius. All models are transformed into a common interfacial rheological form, where the encapsulation is represented by two radius dependent surface properties-effective surface tension and surface dilatational viscosity. Variation of the effective surface tension with radius, specifically having an upper limit (resulting from strain softening or rupture of the encapsulation during expansion), plays a critical role. Without the upper limit, the predicted threshold is extremely large, especially near the resonance frequency. Having a lower limit on surface tension (e.g., zero surface tension in the buckled state) increases the threshold value at twice the resonance frequency, in some cases shifting the minimum threshold toward resonance.

SUBMITTER: Katiyar A

PROVIDER: S-EPMC3259666 | biostudies-other | 2011 Nov

REPOSITORIES: biostudies-other

ACCESS DATA

Similar Datasets

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.

Project description:Microbubbles (MBs) are optimal ultrasound contrast agents because their unique acoustic response allows for exquisite sensitivity in vivo. This unique response is derived from MBs' elasticity that allows them to oscillate differently from surrounding tissues. While the main use of MBs in the clinic is for cardiac and perfusion imaging, imparting MBs with bioresponsive properties would expand their use to detect pathophysiologic changes. This can be achieved by damping MBs' oscillations to silence their signal and rescuing it when they encounter the biomarker of interest to improve detection and specificity of diseases such as deep vein thrombosis (DVT). Here, we demonstrate that conjugating perfluorobutane-filled MBs with hyaluronic acid (HA) and cross-linking HA with biodegradable linkers eliminates harmonic signal because of increased MB stiffness and decreased oscillation. In this proof-of-concept study, we used a reversible pH-sensitive cross-linker to establish and validate this targeted and activatable pH-sensitive MB (pH-MB) platform. Conjugation of HA to MBs and targeting of pH-MBs to CD44-positive cells were validated. Harmonic signal loss due to stiffening of pH-MBs' shell was confirmed using a clinical ultrasound scanner equipped with Cadence contrast pulse sequencing. pH-MBs imaged before and after acidification increased harmonic signal fivefold. Because the cleavage of the cross-linker we used is reversible, harmonic signal was silenced again when the acidic suspension was neutralized, confirming that harmonic signal is dependent on the cross-linked HA. The rate of rise and the magnitude of harmonic signal increase could be manipulated by varying the phospholipid composition and the number of HA cross-linkers, indicating that the platform can be tuned to the desired response needed. In this study, we established the feasibility of using targeted and activatable MBs and plan to apply this platform to aid in the diagnosis and management of patients with DVT and potentially other conditions.

Dataset Information

Excitation threshold for subharmonic generation from contrast microbubbles.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets