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

Worldwide, cardiovascular diseases (e.g. coronary heart disease and stroke) are the leading cause of death. Early detection of cardiac failure symptoms and effective treatment can help reducing health care costs and predict cardiovascular events, which may prevent loss of quality of life, or even loss of life. This early recognition of imminent heart failure is done by evaluating certain risk factors. It is the general assumption that the myocardial stiffness is correlated to diastolic disfunction. During the heart cycle, shear waves are generated by the different moving substances inside the heart, like flowing blood and moving muscle tissue. The propagation velocity of shear waves depends on the tissue stiffness. Thus, by examining shear waves an indication of the myocardial stiffness can be obtained. Currently, no comparable accurate non-invasive method for obtaining an early indication of imminent heart failure is available on the market. In this project, classic phonocardiogram recordings recorded with a custom cost-efficient synchronized recorder system are combined with high frame rate images from the Zonare ZS3 ultrasound imaging machine. It is shown that synchronization with the ZS3 is achieved and a video using ultrasound images and phonocardiogram is composed. This ultimately helps in learning how changing shear wave parameters correlate to imminent heart failure.

This research is a collaboration of the TU Delft and EMC Rotterdam.

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.