For over 50 years, medical ultrasound has been a pioneering force in healthcare, seamlessly blending diagnostic and therapeutic applications. In diagnostics, ultrasound reveals intricate internal structures based on the generation of acoustic pressure waves in the human body and capturing reflections from tissue and body structures, enabling precise anomaly identification. Simultaneously, in therapy, ultrasound utilizes its acoustic prowess for targeted interventions and submillimeter localization in unconventional cancer treatments like proton therapy. The field has shifted significantly with the advent of nonlinear acoustics, exploring wave propagation phenomena. Contrast agents marked a revolutionary leap, enhancing the specificity, sensitivity, and efficiency of diagnostic and therapeutic ultrasound. Microbubbles, as the most conventionally used agents, exhibit strong nonlinear scattering under ultrasonic excitation, making them suitable for CEUS applications. @en

Medical ultrasound is crucial in modern healthcare, with high-frame-rate imaging expanding its applications to both high blood velocities over large fields-of-view and slow-moving blood. Accurate flow measurements require high temporal and spatial resolution, necessitating the use of matrix transducers, which face several challenges depending on the application. For monitoring the brains of preterm babies, challenges include designing ASIC-integrated matrices that meet clinical needs and minimizing cables to ensure unrestricted mother-child contact. For atherosclerosis screening, challenges involve sensor-ASIC integration, developing high-frame-rate data acquisition, and addressing high side-lobe levels in sparse matrices. The objective of this thesis is to address these challenges and develop the necessary technology to enable the use of ultrasound matrix transducers for quantifying blood flow and detecting physiologically abnormal flow patterns and velocities in the two mentioned applications.@en

Ultrasound imaging is a widely available and highly portable real-time, ionizing radiation-free imaging modality used as first-line in multiple areas. Conventionally, its use is focused on providing 2D imaging using ultrasound probes. However, with the introduction of matrix probes, the acquisition of 3D scans became possible enabling the sonographer to accurately interpret the scanned anatomy without needing to build a possibly error prone 3D mental map and thus, decreasing operator-dependency. Although with this 3D imaging, volume estimation accuracy increases and surveillance becomes less difficult, matrix probes are expensive, have a limited field-of-view and produce a low contrast image. This necessitates the sonographer to still build a mental map whenever a portion of an anatomy is not fully visible in a single volumetric scan, leading to more laborious surveillance. Ultrasound stitching is investigated as a potential method to overcome these limitations by tracking multiple ultrasound scans and merging them using their position and orientation coordinates. To this end, this work uses a robotic arm as the selected tracking system for the stitching of 2D xplane ultrasound images. First, the initial clinical application for the system was derived using a combination of literature study and interviews with medical experts which led to the decision of utilizing the robotic arm for liver imaging and biopsy needle guidance. The suitability of this application was validated with the evaluation of the three required stages namely anatomy reconstruction, needle path planning and needle insertion. Two phantoms mimicking lesions and surrounding vessels were fabricated for this purpose. They were firstly reconstructed by manually segmenting the elements of interest from multiple scans, placing these segmented scans in their respective 3D positions and finally applying an alpha-shapes reconstruction algorithm. Once that the centroid of the lesions was calculated and together with the position information about the surface of the phantom obtained with the robotic arm, it was possible to evaluate all the paths that connect the surface with the centroid and subsequently select only the ones that did not pass next to a vessel within a specific distance. Finally and as an extension of using the robotic arm to track the ultrasound probe, the combined tracking of the probe with a needle holder was investigated for the needle insertion stage. The needle holder was used to maintain the needle always in plane with the ultrasound beam and it was placed at a preset distance with respect to the probe. The holder also provided insertion depth information that facilitated the representation of the needle via a line in the visualization environment whose end indicated the position of the needle tip. This position was updated in real-time with the information received from the needle holder while the needle was being inserted. The position of the needle tip was verified by overlapping real-time ultrasound images with the visualized line. Ultimately, to further illustrate the suitability of the robotic arm in a clinical setting, an ex-vivo and a clinical experiment for vessel tracking and reconstruction was performed.

This thesis describes the analysis, design and evaluation of front-end application-specific integrated circuits (ASICs) for 3-D medical ultrasound imaging, with the focus on the receive electronics. They are specifically designed for next-generation miniature 3-D ultrasound devices, such as transesophageal echocardiography (TEE), intracardiac echocardiography (ICE) and intravascular ultrasound (IVUS) probes. These probes, equipped with 2-D array transducers and thus the capability of volumetric visualization, are crucial for both accurate diagnosis and therapy guidance of cardiovascular diseases. However, their stringent size constraints, as well as the limited power budget, increase the difficulty in integrating in-probe electronics. The mismatch between the increasing number of transducer elements and the limited cable count that can be accommodated, also makes it challenging to acquire data from these probes. Front-end ASICs that are optimized in both system architecture and circuit-level implementation are proposed in this thesis to tackle these problems.
The techniques described in this thesis have been applied in several prototype realizations, including one LNA test chip, one PVDF readout IC, two analog beamforming ASICs and one ASIC with on-chip digitization and datalinks. All prototypes have been evaluated both electrically and acoustically. The LNA test chip achieved a noise-efficiency factor (NEF) that is 2.5 × better than the state-of-the-art. One of the analog beamforming ASIC achieved a 0.27 mW/element power efficiency with a compact layout matched to a 150 µm element pitch. This is the highest power-efficiency and smallest pitch to date, in comparison with state-of-the-art ultrasound front-end ASICs. The ASIC with integrated beamforming ADC consumed only 0.91 mW/element within the same element area. A comparison with previous digitization solutions for 3-D ultrasound shows that this work achieved a 10 × improvement in power-efficiency, as well as a 3.3 × improvement in integration density.
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Currently a lot of effort is put into developing matrix arrays which allow for volumetric imaging and new applications. There are however multiple problems. Compared to arrays currently in use which have in the order of 128 elements, matrix arrays can easily contain 1000 to 10000 elements. If all elements would be connected independently, the cable would become very thick. Therefore, beamforming methods are required that can operate with fewer transmit and receive channels. Furthermore, the room for electronics on the chip is limited. So, the required electronics for the beamforming methods should be kept simple.

In this thesis we will propose beamforming methods that are able to operate with fewer channels. This will be done separately for the transmit and receive part, but they do in no way exclude each other. To be able to focus pulsed waves in transmit we propose a method based on Fresnel zone plates which are used in optics to focus continuous wave light. Our method only requires a single continuous-wave excitation signal to be present, which is connected and disconnected on demand to each element. We have evaluated our method with measurements and simulations. As compared to the conventional focusing method, the spatial resolution is not affected by our method, but the Contrast-to-Noise ratio is 5\% lower for shallow depths and up to 20\% lower deeper into the medium. Overall though, the differences were relatively small and so it is clear that our new focusing method works very well. If needed, better results can be obtained by trading in frame rate. In this case the results are almost indistinguishable from the conventional focusing method.

To solve the problem with image formation, we have developed a frequency domain two stage beamforming method for use with matrix arrays, which does not require all element data to be present. This has been done for two matrix types. For the first method we have confirmed with simulations that it performs similar to the respective results obtained with two 2D frequency domain two stage beamforming method that have already been experimentally verified. For the second method we have evaluated the performance with simulations and measurements. Our method was able to obtain a 25\% better spatial resolution as compared to Dynamic Receive Focusing(DRF), without additional artefacts. As an alternative to the last method, we have also developed a frequency domain beamforming method that does require all element data, but only requires a single insonification by a spherical wave. This method did perform worse than the method discussed before in both simulations and measurements, but it does outperform DRF applied to spherical wave data.