Non-linear Acoustic Characterization of Microbubbles and Nanobubbles

Non-linear contrast-enhanced ultrasound can provide high contrast images by enhancing the non-linear signals from bubble oscillations. In this work, we developed a methodology to detect individual bubble scattering using focused transducers with dilute bubble solutions. Microbubbles and nanobubbles were made with five different lipid shell compositions. Their structure is altered through additional components added to the shell that affect their stability. Dilute samples of bubbles were sonicated at 25 MHz with 30 cycles using a commercial high frequency ultrasound instrument with a pressure range of 75 kPa to 3 MPa. Criteria were developed to ensure signals were only classified if they contained an isolated bubbles’ response. The response of the bubbles of different shell compositions were compared using analysis tools developed. There were no observable differences in the non-linear behaviour between the different shells. However, when comparing microbubbles to nanobubbles differences involving signal count, stability and harmonic amplitudes were observed.

Non-linear Acoustic Characterization of Microbubbles and Nanobubbles

Non-linear contrast-enhanced ultrasound can provide high contrast images by enhancing the non-linear signals from bubble oscillations. In this work, we developed a methodology to detect individual bubble scattering using focused transducers with dilute bubble solutions. Microbubbles and nanobubbles were made with five different lipid shell compositions. Their structure is altered through additional components added to the shell that affect their stability. Dilute samples of bubbles were sonicated at 25 MHz with 30 cycles using a commercial high frequency ultrasound instrument with a pressure range of 75 kPa to 3 MPa. Criteria were developed to ensure signals were only classified if they contained an isolated bubbles’ response. The response of the bubbles of different shell compositions were compared using analysis tools developed. There were no observable differences in the non-linear behaviour between the different shells. However, when comparing microbubbles to nanobubbles differences involving signal count, stability and harmonic amplitudes were observed.

Ultra-broadband axicon transducer for optoacoustic endoscopy

Image performance in optoacoustic endoscopy depends markedly on the design of the transducer employed. Ideally, high-resolution performance is required over an expanded depth of focus. Current optoacoustic focused transducers achieve lateral resolutions in the range of tens of microns in the mesoscopic regime, but their depth of focus is limited to hundreds of microns by the nature of their spherical geometry. We designed an ultra-broadband axicon detector with a 2 mm central aperture and investigated whether the imaging characteristics exceeded those of a spherical detector of similar size. We show a previously undocumented ability to achieve a broadband elongated pencil-beam optoacoustic sensitivity with an axicon detection geometry, providing approximately 40 μm-lateral resolution maintained over a depth of focus of 950 μm—3.8 times that of the reference spherical detector. This performance could potentially lead to optoacoustic endoscopes that can visualize optical absorption deeper and with higher resolution than any other optical endoscope today.

Acoustic wave focusing by doubly curved origami-inspired arrays

Spherically focused transducers have been long relied on to target acoustic energy delivery. Yet, these structures have limitations with respect to size and mobility for medical treatment applications. Recent developments in the field of reconfigurable structures reveal that the ancient art of origami inspires new platforms by which to enable spherical shapes that are additionally foldable for ease of transport. This research explores the opportunities for a unique, flat foldable doubly curved tessellated array to enable wave focusing capability similar to an ideal medical transducer shape: the spherical cap transducer. An analytical model of the doubly curved array is created and validated against data collected from a proof-of-concept array. The model is then leveraged to understand how the array design and complexity relatively govern the wave focusing capability. The findings show that doubly curved acoustic arrays do not require excessive facet refinement to achieve wave focusing similar to nominal spherically focused transducers. Yet, the optimal frequencies for which such capability is borne out vary substantially on the basis of array design. The discoveries of this research motivate future consideration of flat foldable doubly curved acoustic arrays for potential implementation into medical transducer development for hard-to-access surgical treatments.

Modeling Flaw Pulse-Echo Signals in Cylindrical Components Using an Ultrasonic Line-Focused Transducer with Consideration of Wave Mode Conversion

Investigations on flaw responses can benefit the nondestructive testing of cylinders using line-focused transducers. In this work, the system function, the wave beam model, and a flaw scattering model are combined to develop an ultrasonic measurement model for line-focused transducers to predict flaw responses in cylindrical components. The system function is characterized using reference signals by developing an acoustic transfer function for line-focused transducers, which works at different distances for both planar and curved surfaces. The wave beams in cylindrical components are modeled using a multi-Gaussian beam model, where the effects of wave mode conversion and curvatures of cylinders are considered. Simulation results of wave beams are provided to analyze their propagation behaviors. The proposed ultrasonic measurement model is certified from good agreement between the experimental and predicted signals of side-drilled holes. This work provides guidance for evaluating the detection ability of line-focused transducers in cylindrical component testing applications.

Nonuniform Bessel-Based Radiation Distributions on A Spherically Curved Boundary for Modeling the Acoustic Field of Focused Ultrasound Transducers

Therapeutic focused ultrasound is a technique that can be used with different intensities depending on the application. For instance, low intensities are required in nonthermal therapies, such as drug delivering, gene therapy, etc.; high intensity ultrasound is used for either thermal therapy or instantaneous tissue destruction, for example, in oncologic therapy with hyperthermia and tumor ablation. When an adequate therapy planning is desired, the acoustic field models of curve radiators should be improved in terms of simplicity and congruence at the prefocal zone. Traditional ideal models using uniform vibration distributions usually do not produce adequate results for clamped unbacked curved radiators. In this paper, it is proposed the use of a Bessel-based nonuniform radiation distribution at the surface of a curved radiator to model the field produced by real focused transducers. This proposal is based on the observed complex vibration of curved transducers modified by Lamb waves, which have a non-negligible effect in the acoustic field. The use of Bessel-based functions to approximate the measured vibration instead of using plain measurements simplifies the rationale and expands the applicability of this modeling approach, for example, when the determination of the effects of ultrasound in tissues is required.