Tools and Techniques for Advanced Beamforming in Contrast Enhanced Echocardiography

Ischaemic Heart Disease (IHD) is the leading cause of deaths globally. In the U.K., current National Institute for Health and Care Excellence (NICE) guidelines recommend the use of Computed Tomography Coronary Angiography (CTCA) as the first line of testing for patients with chest pain due to suspected IHD. Due to the prevalence of IHD, however, an 8-fold increase in the number of CTCA scans would be required to meet these recommendations.

Alternative technologies must be developed and evaluated to meet the vast burden of IHD. Microbubbles are gas-filled bubbles encapsulated in a shell and are typically 1 - 10 um in diameter. A microbubble can be used as an Ultrasound Contrast Agent (UCA) in Contrast Enhanced Echocardiography (CEE) because of an acoustic impedance mismatch with blood. Emerging functional imaging techniques, incorporating microbubbles to quantify blood flow, could provide an alternative non-invasive assessment of IHD. In this work, an apparatus was designed to characterise the acoustic scattering properties of microbubbles.

Despite the promise of these techniques, the clinical relevance of 3-Dimensional (3D) anatomical imaging cannot be ignored. 3D volumetric imaging offers advantages over 2-Dimensional (2D) imaging for microbubble localisation and tracking. The poor lateral and elevational resolution of 3D beamforming with a 2D matrix array probe, however, is a major challenge limiting adoption for anatomical imaging and for microbubble localisation. In this work, a framework was developed for 3D volumetric imaging simulation.

Although adaptive beamforming algorithms can improve the lateral and elevational resolution, they often exhibit a high computational complexity. The additional complexity in 3D imaging, due to the increased data burden of a 2D matrix array, makes implementing an adaptive 3D beamformer challenging. In this work, a high resolution, accelerated , 2D beamformer was developed, and later extended to 3D.

In summary, this work concerns the design of experimental and simulation tools to facilitate the development of imaging schemes for CEE and 3D volumetric imaging. It also consists of the development of a high-resolution beamformer for applications in 3D echocardiography.