Ultrasound tomographic reconstruction using sonothrombolysis hardware.

Author(s)

Roberto Costa Ceccato

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
• Defense date: 2025-06-18

Examining board members

Sérgio Shiguemi Furuie; Diego Armando Cardona Cardenas; Alexandre Kawano; Wilson Mathias Junior; John Andrew Sims

• Advisor: Sérgio Shiguemi Furuie; Chi Nan Pai

Abstract

Medical imaging is responsible for the vast majority of the modern medicine advancement. Techniques such as computed tomography (CT), ultrasound (US), and magnetic resonance imaging (MRI) facilitate both in vivo studies, and rapid and accurate diagnoses. Within this field, ultrasound has played a significant role in medical diagnostics since the second half of the 20th century. Typically, image reconstruction methods that use ultrasound as the physical signal source result in qualitative images. Since these methods have to assume a homogeneous medium with respect to the speed of sound (SoS), they tend to suffer from artifacts and aberrations in the shapes or dimensions of the imaged region. The search for efficient and viable methods for quantitative medical ultrasound image reconstruction has been ongoing for a long time. The main motivations for this effort lie in the possibility that, once in possession of a map of some mediums physical characteristics, a more accurate diagnosis can be made with a nearly unambiguous characterization of the tissue and a reduction in aberrations or artifacts in the final image. The primary methods for quantitative US image reconstruction include elastography, Full Waveform Inversion (FWI) methods, time of flight in transmission mode (TFTM) tomography, and time of flight in echo mode (TFEM) tomography. In addition to the diagnostic use of ultrasound, therapeutic methods are also of great importance. In cardiology, sonothrombolysis emerges as a promising alternative for dissolving thrombi. The procedure utilizes high-power focused ultrasound beams to induce cavitation of microbubbles injected into the patients bloodstream. In this context, the present work developed and evaluated the limits of performing quantitative medical image reconstruction using ultrasound signals captured with the geometric setup of a sonothrombolysis device. This highly specialized equipment is being researched and developed by the Biomedical Engineering Laboratory at the University of Sao Paulo. In order to enable an accurate identification of tissues and the correction of aberrations caused by the assumed constant speed of sound, the reconstructed image will associate a sound speed value for each point in the discretized space. Considering that the geometry of the sonothrombolysis device does not have opposing transducers, the reconstruction principle adopted was TFEM, as it relies solely on echoes. Additionally, the device features sparsely distributed transducers, aiming to cover the cardiac region while reducing manufacturing complexity. This design choice introduced an additional challenge not addressed in the literature, which typically considers dense arrays to avoid phase-wrapping issues. The proposed methodology involved the detailed modeling of the received signal and the development of acceptance criteria for temporal measurements, in addition to numerical experiments conducted on three phantoms of increasing complexity for validation purposes. Ultrasound propagation was simulated using the k-Wave computational tool for MATLAB, considering different transducer configurations in terms of the number of elements (8, 32, 64, 128, and 256) and central frequencies (500 kHz, 1 MHz, and 2 MHz). The main focus of the methodology was to develop the theoretical foundation, particularly through the modeling of the received signal, to support the investigation, guide the design of algorithms for sparsely distributed transducers in TFEM USCT, and validate the proposed approaches. The results suggests that quantitative TFEM ultrasound computed tomography image reconstruction is feasible within a sonothrombolysis hardware setup, provided that appropriate design choices are made regarding element count and frequency. An extensive discussion about the design choices is provided in this study. Summarily, findings suggest that the use of sparse transducer arrays is a viable strategy for TFEM USCT. It is expected that, in future work, creating a more accurate velocity distribution map within the medium will correct most of the aberrations and artifacts, leading to the possibility of optimizing the focusing of pulses used to cavitate the microbubbles and cause sonothrombolysis. (AU)

• FAPESP's process: 21/13997-0 - Ultrasound Tomographic reconstruction using sonothrombolysis hardware
• Grantee: Roberto Costa Ceccato
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)