Acoustic detection of microbubble resonance

Thomas, David Hurst; Looney, Pádraig; Steel, R.; Pelekasis, N.; McDicken, W.N.; Anderson, Thomas; Sboros, Vassilis

doi:10.1063/1.3151818

Cited by 28 publications

(29 citation statements)

References 19 publications

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“…Figure 8 shows the median fundamental and 2 nd harmonic RMS scattered pressure, indicating fundamental dominated scatter occurs below 335 kPa and above 710 kPa. The large proportion of fundamental dominated signals at low acoustic pressures is reminiscent of resonance, as was found for lipid-shelled Definity (Lantheus Medical Imaging, North Billarica, MA) MBs (Thomas et al 2009). Smaller and/or cracked biSphere MBs become detectable as the acoustic pressure increases.…”

Section: Discussionmentioning

confidence: 91%

“…Smaller and/or cracked biSphere MBs become detectable as the acoustic pressure increases. The number of harmonic dominated signals, which have previously been observed to be a characteristic of scatter below prime resonance (Thomas et al 2009), increases to a maximum at 550 kPa. Above 710 kPa, there is an increase again of fundamental dominated signals with the increase in acoustic pressure, which agrees with spectral broadening at resonance (Shi et al 1997).…”

Section: Discussionmentioning

confidence: 92%

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The Acoustic Scatter from Single biSphere Microbubbles

Thomas

Butler

Dermitzakis

et al. 2010

Ultrasound in Medicine & Biology

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Section: Discussionmentioning

confidence: 91%

Section: Discussionmentioning

confidence: 92%

The Acoustic Scatter from Single biSphere Microbubbles

Thomas

Butler

Dermitzakis

et al. 2010

Ultrasound in Medicine & Biology

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“…4 The transient resonant response of microbubbles close to resonance differs for insonification with up and down frequency sweeps. 5,6 Capitalizing on this asymmetry, we present a contrast imaging mode that provides good contrast to tissue ratio (CTR) at clinically approved concentrations of UCA.We investigated the performance of IVUS chirp imaging on different phantoms as well as an atherosclerotic human coronary artery ex vivo. Contrast chirp reversal imaging was evaluated using a channel phantom perfused with a commercial UCA.…”

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confidence: 99%

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confidence: 99%

Intravascular ultrasound chirp imaging

Maresca

Jansen

Renaud

et al. 2012

Applied Physics Letters

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We demonstrate the feasibility of intravascular ultrasound (IVUS) chirp imaging as well as chirp reversal ultrasound contrast imaging at intravascular ultrasound frequency. Chirp excitations were emitted with a 34 MHz single crystal intravascular transducer and compared to conventional Gaussian-shaped pulses of equal acoustic pressure. The signal to noise ratio of the chirp images was increased by up to 9 dB relative to the conventional images. Imaging of contrast microbubbles was implemented by chirp reversal, achieving a contrast to tissue ratio of 12 dB. The method shows potential for intravascular imaging of structures in and beyond coronary atherosclerotic plaques including vasa vasorum. Atherosclerosis is a chronic systemic disease of the arterial wall and a leading cause of premature death worldwide. Most cardiac adverse events result from the rupture of a vulnerable atherosclerotic plaque and subsequent thrombosis in the coronary vascular tree.1 It is recognized that the formation of new microvessels in the arterial wall is critical to the progression of plaques due to red blood cell leakage and constitutes an important marker of plaque vulnerability.2 These networks of microvessels, ranging in diameter from 20 to 100 lm, are referred to as vasa vasorum (VV).As of today, there are no clinically available tools for detecting VV in coronary artery plaques. Goertz et al. 3 reported the feasibility of VV imaging in animals by using an experimental intravascular ultrasound (IVUS) catheter and micron sized bubbles as ultrasound contrast agent (UCA) to reveal microvasculature which lies below the resolution limit. The method relied on the strong nonlinear response of a high concentration bolus of UCA compared to tissue.In this letter, we develop chirp IVUS, with the dual objective of extending the viewing depth, and implementing chirp reversal contrast imaging in a manner that is applicable on a conventional IVUS catheter. At a given mechanical index (MI) and frequency bandwidth, chirp excitations carry more energy than conventional imaging pulses. As a result, chirp images display an extended tissue penetration depth. To date, ultrasound chirp imaging was implemented in noninvasive clinical imaging only. 4 The transient resonant response of microbubbles close to resonance differs for insonification with up and down frequency sweeps. 5,6 Capitalizing on this asymmetry, we present a contrast imaging mode that provides good contrast to tissue ratio (CTR) at clinically approved concentrations of UCA.We investigated the performance of IVUS chirp imaging on different phantoms as well as an atherosclerotic human coronary artery ex vivo. Contrast chirp reversal imaging was evaluated using a channel phantom perfused with a commercial UCA.The experimental intravascular imaging system consisted of a mechanically rotated single element IVUS transducer (single-crystal lead magnesium niobate-lead titanate; PMN-PT, 7 active surface 0.5 Â 0.5 mm 2 , center frequency 34 MHz, À6 dB bandwidth 60%, and 2 mm natural focus) mo...

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“…The scattering cross-section of LCMB can be maximized when driven at resonance; thus, determining the resonance frequency of LCMB has been the subject of numerous studies, both theoretical and experimental. [6][7][8][9][10] Theoretical models have shown that the resonance frequency depends upon both the microbubble radius and the viscoelastic properties of the outer shell. Early models of encapsulated microbubbles defined the outer shell as a viscoelastic solid [11][12][13][14] or a viscous Newtonian fluid, 15,16 with material properties that were uniform throughout the shell.…”

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confidence: 99%

Acoustic investigation of pressure-dependent resonance and shell elasticity of lipid-coated monodisperse microbubbles

Gong

Cabodi

Porter

2014

Applied Physics Letters

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In this study, frequency-dependent attenuation was measured acoustically for monodisperse lipidcoated microbubble suspensions as a function of excitation pressure and radius. The resonance frequency was identified from the attenuation spectra and had an inverse relationship with mean microbubble diameter and excitation pressure. A reduction in the estimated shell elasticity constant from 0.50 N/m to 0.29 N/m was observed as the excitation pressure was increased from 25 kPa to 100 kPa, respectively, which suggests a nonlinear relationship exists between lipid shell stiffness and applied strain. These findings support the viewpoint that lipid shells coating microbubbles exist as heterogeneous mixtures that undergo dynamic and rapid variations in mechanical properties under applied strains. V C 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4865805] Lipid-coated microbubbles (LCMB) have proven to be very effective contrast agents for diagnostic ultrasound imaging. 1-5 The scattering cross-section of LCMB is several orders of magnitude greater than tissue, resulting in an exceptional contrast-to-tissue ratio in diagnostic ultrasound images. The scattering cross-section of LCMB can be maximized when driven at resonance; thus, determining the resonance frequency of LCMB has been the subject of numerous studies, both theoretical and experimental. 6-10 Theoretical models have shown that the resonance frequency depends upon both the microbubble radius and the viscoelastic properties of the outer shell. Early models of encapsulated microbubbles defined the outer shell as a viscoelastic solid 11-14 or a viscous Newtonian fluid, 15,16 with material properties that were uniform throughout the shell. However, several studies have reported measurements of pressure-dependent attenuation in suspensions of lipid-coated microbubbles, 17-20 suggesting that the shell viscoelastic properties are in fact non-Newtonian. We hypothesized that the pressure-dependent behavior may be due to non-uniform shell viscoelastic properties, which may vary when the microbubbles are driven acoustically. Fluorescent images of lipid-coated microbubbles have shown that the phase of the lipid shell can be spatially homogeneous or heterogeneous, depending upon the length of the lipid hydrocarbon chains. 21,22 Furthermore, documented studies of lipid-coated microbubbles during gradual dissolution (over seconds) have reported that the lipid shell can fold, buckle, and shed as the lipid shell is compressed. 23,24 While informative, it remains unclear if these changes in the shell microstructure will occur during microbubble oscillation at megahertz (MHz) frequencies. Provided these structural changes do occur, they may impact the shell viscoelastic properties, which may be reflected by changes in the frequency response of microbubbles to acoustic excitation.Historically, researchers have combined theoretical predictions and experimental measurements of the frequencydependent attenuation coefficient to estimate the shell viscoelastic properties. 15,25-2...

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Acoustic detection of microbubble resonance

Cited by 28 publications

References 19 publications

The Acoustic Scatter from Single biSphere Microbubbles

The Acoustic Scatter from Single biSphere Microbubbles

Intravascular ultrasound chirp imaging

Acoustic investigation of pressure-dependent resonance and shell elasticity of lipid-coated monodisperse microbubbles

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