Development and real-time implementation of novel 2-D and 3-D imaging techniques on a research scanner

In the last decades, ultrasound imaging systems have become more and more popular thanks to their capability to investigate tissues in safe, cost effective, and non-invasive way. Their role in diagnostic imaging has become fundamental in several medical specialties, thanks also to the introduction of advanced echographic systems fostered by the efforts of several research laboratories around the world. Such efforts are more frequently based on the use of special research scanners, characterized by flexible hardware and programmable software and firmware. These features have been demonstrated ideal for the implementation and test of new methods, such as high frame-rate (HFR) imaging, color flow imaging (CFI), vector Doppler imaging, and 3 D imaging. Especially HFR and 3 D imaging have recently attracted great interest, but they are technically demanding since they involve either the formation of thousands of images per second, or the use of 2-D probes having a large number of elements. Therefore, great challenges must be faced for effective real-time implementation of 3 D and HFR imaging methods. My PhD activity aimed to implement and test advanced 2 D and 3 D ultrasound imaging modalities on an open research scanner called ULA OP 256. In the first part of my work, a new ultrasound imaging modality called Virtual real-time (VRT) was introduced through the modification of the firmware and software of the research scanner ULA-OP 256. With this modality, during a real-time (RT) investigation, the scanner initially acquires and stores in its memory up to 20 s of raw echo data. On user demand, the scanner can be switched to VRT mode: the stored data are re processed by the same resources used in RT but at different (typically lower) rates and, possibly, with different processing algorithms and parameters. In this way, contingent difficulties of image interpretation (especially in presence of rapidly moving phenomena), or possible computational limitations imposed by hardware during continuous RT processing can be overcome. The VRT modality has been demonstrated useful in different applications, for example, to implement a high-PRF version of the Multiline vector Doppler (MLVD) method, and a High- rame-rate CFI method, characterized by enhanced temporal and spatial resolution. The second part of my work included the software upgrade of ULA OP 256; it enabled the use of 2 D probes and the implementation of 3 D scanning methods. The ULA OP 256 can now be coupled to 2 D probes with arbitrary geometries, including matrix and sparse arrays. Furthermore, the scanner is now capable of simultaneously imaging multiple planes with programmable rotational angles. Novel approaches based on a sparse spiral array probe have been implemented and tested for different applications. For example, bi-plane imaging was evaluated for robust flow mediated dilation exams. Real-time 3 D spectral Doppler analysis was also performed. Here, two planes with programmable rotational angles were scanned to produce corresponding B-Mode images, over which multiple Doppler lines could be arbitrarily set to obtain the relative Multigate spectral Doppler (MSD) profiles. Finally, the last part of my work was specifically dedicated to the technical problems involved by HFR 3 D imaging. The management of (several) hundreds of transducer elements of a 2 D probe yields a huge amount of echo data: this makes complex and computationally expensive the processing of data volumes including thousands of lines, especially if performed at HFR. As a case report, the requirements of the main processing stages involved in ULA OP 256 receiver have been thoroughly investigated to detect and, possibly, solve the main bottlenecks. The study has evidenced that the star architecture that digitally interconnects the eight front-end boards of ULA OP 256 may frequently encounter data transfer bandwidth saturation that limits the overall performance in terms of frame/volume rate. A new architecture for data transfer has been proposed and shown effective to reduce the bandwidth requirements and thus, increase the performance of the scanner.