Tomography across scales: Knowledge transfer from seismology to imaging breast tissue with ultrasound

Abstract

Wave propagation is extensively used to understand the internal structure of media that are not accessible to direct observations. Seismology and medical ultrasound imaging are good examples of this. The former uses observations of seismic waves at the Earth's surface to increase our knowledge about its interior. This is crucial, for instance, to improve our understanding about the Earth's dynamics and evolution. Medical ultrasound, on the other hand, uses observations of acoustic waves, emitted and recorded at the surface of human bodies, to visualize internal body structures. This has become an essential screening tool, useful for diagnostic examination.This thesis presents an interdisciplinary work between seismology and medical ultrasound. In particular, we focus on transferring knowledge from seismic tomography to Ultrasound Computer Tomography (USCT), an emerging technology that holds great potential for early-stage breast cancer diagnosis. Here, the human breast is surrounded by transducers that collect transmitted and reflected ultrasound signals. This information is then used to obtain 3D quantitative images of acoustic tissue properties, which enable non-invasive tissue characterization and improve the specificity of standard imaging modalities. Current challenges in USCT mostly consist in providing a diagnostic tool with high accuracy (comparable to magnetic resonance imaging) and affordable computational and acquisition cost for clinical practice, the target being a maximum time of 15 minutes per patient. Despite the vastly different scale, seismic and medical ultrasound tomography share fundamental similarities that allow us to address these challenges from the stand point of the seismologist.We first introduce finite-frequency traveltime tomography to medical ultrasound. In addition to being computationally tractable for 3D imaging at high frequencies, the method has two main advantages: (1) It correctly accounts for the frequency dependence and volumetric sensitivity of traveltime measurements, which are related to off-ray-path scattering and diffraction. (2) It naturally enables out-of-plane imaging and the construction of 3D images from 2D slice-by-slice acquisition systems. Our method rests on the availability of calibration data measured in water, used to linearize the forward problem and to provide analytical expressions of cross-correlation traveltime sensitivity. We present a memoryefficient implementation suitable for arbitrarily large-scale domains, and we discuss its extension to amplitude tomography.To adapt existing acquisition systems to new imaging techniques, we then introduce optimal experimental design methods. These provide a systematic and quantitative framework i to (1) evaluate the quality of different designs in terms of uncertainties in the estimated tissue parameters and (2) optimize the configuration with respect to predefined design parameters, for example the position of transducers on the scanning device. Our first application presents a cost-effective 3D configuration o...

Towards Attenuation Imaging with Computed Ultrasound Tomography in Echo Mode (CUTE)

“…However, tissue can also contain specular reflectors that backscatter waves in directions that depend on the transmitted plane waves. Secondly, we neglect amplitude variations caused by SoS heterogeneities resulting from geometrical focusing/defocusing, diffraction, and interference effects [20], [21]. Furthermore, such heterogeneities can also introduce aberration artifacts in beamformed images, thereby unfocusing detected echoes and affecting their amplitudes.…”

Physical and Mechanical Properties of Herrnholz Granite: An Ideal Experimental Material

“…More detail and the mathematical description of this inversion problem have been described in Ref. [39]; hence, they were not explained here.…”

Compact reverse time migration: A real-time approach for full waveform ultrasound imaging for breast

“…Furthermore, MRI requires expensive instrumental setups that hinder its use on a regular basis (Duric et al, 2013;Patel et al, 2017). In contrast, ultrasound computer tomography is a more preferred method for routine screening of breast cancer because of its favourable properties, such as non-invasive, radiation-free, low instrumental cost (Berg et al, 2008;Duric et al, 2005;Korta Martiartu, 2020). The automatic whole breast ultrasound system (ABUS) is a dedicated device for cancer screening in dense breast tissue.…”

“…The adoption of the wave equation helps the algorithm exploit broadband data. Additionally, it can also utilize more complex models to capture fine-scale (sub-Fresnel zone) heterogeneities (Guasch et al, 2020;Korta Martiartu, 2020). The ray-based method is incapable in this aspect because it assumes a simple (smooth) propagation model (sound speed model and attenuation model).…”