A formulation of the coupled viscoacoustic-viscoelastic wave equation is proposed for modeling the propagation of ultrasound waves in soft tissue-bone systems using the spectral-element method. Including the attenuative effects within the skull is of considerable relevance across a variety of ultrasound applications due to the highly dissipative nature of the trabecular bone. The...
We present a Full Waveform Inversion (FWI) approach designed to simultaneously identify interfaces and reconstruct sound speeds within layered media. This method hinges on synthetic data produced from our forward simulation. By reformulating the inverse problem into a Partial Differential Equation (PDE) constrained optimization, governed by the wave equation, we utilize a gradient descent...
The inverse acoustic scattering problem refers to the mathematical imaging problem of reconstructing the speed of sound in a medium from a collection of scattered waves. A popular approach is full waveform inversion, which addresses this non-linear inverse problem iteratively without simplifying the underlying mathematical model leading to highly accurate solutions at the expense of increased...
Photoacoustic tomography (PAT) is a hybrid imaging technique based on the photoacoustic effect. The PAT forward problem can be modelled as an initial value problem for the free space wave equation. The PAT inverse problem aims to recover an initial pressure from pressure time series recorded at sensors placed outside the region of interest. Despite the advances made in the recent years...
Full waveform inversion (FWI) is a reconstruction algorithm recently explored in the field of ultrasound computed tomography (USCT), for high resolution 3-dimensional imaging of the breast. Ultrasound tomography-based imaging, devoid of radiation, can be a safe tool for breast cancer screening and diagnostics. FWI usually inverts for single parameter, typically speed of sound. However,...
Background:
Ultrasound Computed Tomography (USCT) based on circular arrays provides richer and more detailed information compared to traditional ultrasound imaging, which has attracted extensive attention. The delay-and-sum (DAS) method, along with its related weighted improvement strategies, stands as the mainstream signal beamforming approach in this domain. In the DAS method, the...
Ultrasound attenuation maps are an important imaging modality of medical ultrasound tomography. Many approaches however only put focus on the attenuation at a specific or dominant frequency with small bandwidth or the broad band attenuation of a signal with large bandwidth. Yet, attenuation by tissue is typically considered to be frequency dependent. In the literature this is modelled linearly...
Ultrasound tomography (USCT) is an exciting new technology with several active research groups investigating new algorithms, devices and applications worldwide. To fully utilise the 3D interaction of the ultrasound fields with the object to be imaged, we are focusing our research on 3D USCT systems. We have realised a pseudo-randomly sampled hemispherical 3D USCT device (3D USCT III) with...
Focused ultrasound is used in a therapeutic treatment (HIFU) and uses ultrasound waves to non-invasively destroy malignant cells inside the human body. The technique works by sending a high-energy beam of ultrasound into the tissue using a focused transducer. Numerically modelling HIFU presents a problem due to nonlinear effects leading to the formation of harmonics of the source frequency....
Computed Ultrasound Tomography in Echo Mode (CUTE) maps the tissue’s speed-of-sound (SoS) using conventional handheld limited-aperture echo ultrasound (US) probes. The technique consists of a sequence of steps that can be performed in real time: beamforming of US images under varying transmit- and receive steering angles, detection of echo shift between different angle combinations, SoS...
