Sound bullets for enhanced biomedical ultrasound systems

Lead Research Organisation: University College London
Department Name: Mechanical Engineering


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Description Finite element analysis (FEA) was employed to model the dynamics of granular chains with signals relevant to biomedical ultrasound. This yielded good agreement with the discrete mechanics solution and demonstrated that the multiple collisions which occur between the beads of the chain could be accurately modelled. Good agreement with experimental results was also achieved. The coupling of this sinusoidally excited granular chain to an acoustic medium was subsequently achieved, thus enabling the prediction of the acoustic pressure inside the medium. This model was used to carry out sensitivity analyses of the system to key input parameters, including excitation frequency and amplitude, sphere diameter and the number of spheres present in the chain. Granular chains were excited at one end using tone burst displacement signals with fundamental frequencies of 73 kHz and 100 kHz. The final sphere of the chain was assumed to be in contact with a cylindrical vitreous carbon layer, coupled to a half-space of water. Using the finite element method, it was possible to extract normal velocities at the fluid structure interface, which were then fed into a Kirchhoff Retarded Potential Integral formulation to predict the acoustic pressure in the fluid resulting from a 21 element 1D focused array of granular chains. The sensitivity analyses identified configurations whereby, under tone burst excitation conditions, a train of impulses could be propagated into an acoustic medium, with harmonic rich content up to 2 MHz and with peak positive pressures of up to 4.5 MPa. Axial and lateral scans of field pressure quantities demonstrate proof-of-principle of generation of highly focused fields, with submillimeter beamwidths and a quasi-absence of side lobes.

Potential applications of the transduction mechanism investigated are now discussed. Applications of this device to thermal ablation of soft tissue could be problematic if a large volume is to be destroyed. Nevertheless, noninvasive applications which require a very small volume to be precisely ablated could benefit from such a device. A second potential application of this transduction mechanism lies in selective cytolysis of cancer cells. It has been reported that malignant cells possess different biomechanical properties to healthy cells, and that malignant cells could be more susceptible to radiation force effects from ultrasound. Conventional ultrasonic transducers operated in the 0.5?5 MHz range do not generally possess narrow enough beamwidths to selectively induce cell lysis effects and distinguish between nonmalignant and malignant cells. High-frequency (18 MHz) devices have been suggested for inducing cytolysis effects in human prostate cancer cells 22RV1 without heat or cavitation. The transduction mechanism based on an array of granular chains could potentially serve as a similar purpose, and apply radiation force directly to cells or tissues. Another potential application of the device lies in delivering short acoustic pulses for histotripsy applications. However, an array with a larger amount of granular chains will be required to produce the necessary peak negative pressures. Finally, as a result of the narrow beamwidths generated and the quasi-absence of side lobes, there exists the possibility to generate microscopic lesions in a precise fashion.
Exploitation Route As this is a collaboration with two other research groups (at Warwick and Leeds universities) the findings of our modelling activities have been fed into the experimental work being carried out by our collaborators. The design of their experiments and the analysis of their results have been informed by our modelling work.
Sectors Healthcare

Description As this grant was part of a project led by Professor Hutchins at Warwick University, please see the impact description provided for EP/K030159/1.
Sector Healthcare
Impact Types Societal,Economic