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Ultrasound medical imaging stands out among the other diagnostic imaging modalities for its patient-friendliness, high temporal resolution, low cost, and absence of ionizing radiation. On the other hand, it may still suffer from limited detail level, low signal-to-noise ratio, and narrow field-of-view. In the last decade, new beamforming and image reconstruction techniques have emerged which aim at improving resolution, contrast, and clutter suppression, especially in difficult-to-image patients. Nevertheless, achieving a higher image quality is of the utmost importance in diagnostic ultrasound medical imaging, and further developments are still indispensable. From this point of view, a crucial role can be played by novel beamforming techniques as well as by non-conventional image formation techniques (e.g., advanced transmission strategies, and compounding, coded, and harmonic imaging). This Special Issue includes novel contributions on both ultrasound beamforming and image formation techniques, particularly addressed at improving B-mode image quality and related diagnostic content. This indeed represents a hot topic in the ultrasound imaging community, and further active research in this field is expected, where many challenges still persist.
In this thesis, we define a mathematical framework for the beamforming of ultrasonic data compatible with Compressive Sensing. Then, we investigate its capabilities on simple simulations in terms of resolution and super-resolution. Finally, we adapt t-CBF to real-life ultrasonic data. In particular, we reconstruct 2D cardiac images at a frame rate 100-fold higher than typical values.
This book deals with the concept of medical ultrasound imaging and discusses array signal processing in ultrasound. Signal processing using different beamforming techniques in order to achieve a desirable reconstructed image and, consequently, obtain useful information about the imaging medium is the main focus of this book. In this regard, the principles of image reconstruction techniques in ultrasound imaging are fully described, and the required processing steps are completely expanded and analyzed in detail. Simulation results to compare the performance of different beamformers are also included in this book to visualize their differences to the reader. Other advanced techniques in the field of medical ultrasound data processing, as well as their corresponding recent achievements, are also presented in this book. Simply put, in this book, processing of medical ultrasound data from different aspects and acquiring information from them in different manners are covered and organized in different chapters. Before going through the detailed explanation in each chapter, it gives the reader an overview of the considered issue and focuses his\her mind on the challenge ahead. The contents of the book are also presented in such a way that they are easy for the reader to understand. This book is recommended for researchers who study medical ultrasound data processing.
Ultrasound medical imaging stands out among the other diagnostic imaging modalities for its patient-friendliness, high temporal resolution, low cost, and absence of ionizing radiation. On the other hand, it may still suffer from limited detail level, low signal-to-noise ratio, and narrow field-of-view. In the last decade, new beamforming and image reconstruction techniques have emerged which aim at improving resolution, contrast, and clutter suppression, especially in difficult-to-image patients. Nevertheless, achieving a higher image quality is of the utmost importance in diagnostic ultrasound medical imaging, and further developments are still indispensable. From this point of view, a crucial role can be played by novel beamforming techniques as well as by non-conventional image formation techniques (e.g., advanced transmission strategies, and compounding, coded, and harmonic imaging). This Special Issue includes novel contributions on both ultrasound beamforming and image formation techniques, particularly addressed at improving B-mode image quality and related diagnostic content. This indeed represents a hot topic in the ultrasound imaging community, and further active research in this field is expected, where many challenges still persist.
"Due to its inexpensive and non-invasive nature, ultrasound imaging has become the preferred medical imaging modality. Despite its high demand, its use is limited due to the fact that ultrasound images suffer from noise and image artifacts such as sidelobes and reverberation artifacts. Over the past decades, a vast amount of research has been carried out to improve the resolution and contrast of images through various techniques that are based on adjusting the shape of the ultrasonic excitation, or improving the so-called beamforming function at the receiver side, or utilizing image post-processing. In this thesis, there are three novel ultrasound imaging methods discussed. The first technique, named Compressive Ultrasound or CU is based on applying randomized transform to the RF data and thereafter compressing the data, thus reducing the hardware requirements. The random modulation at the receiver side ensures that the frequency content is spread across the entire spectrum, thus conserving information. The results from this method are compared to traditional ultrasound B-mode images.The proposed method exhibits imaging contrast and resolution similar to traditional ultrasound but with much reduced computational complexity compared to compressive sensing techniques. Next, a coherent imaging methodology referred to as Ultrasound Coherent Imaging (UCI) is presented. This method is based on model characterization of the medium being imaged and convex optimization methods for image reconstruction. The UCI method deploys front-end architectures and post-processing steps of image reconstruction that are dramatic departure from conventional approaches and has the potential to disrupt the state-of-the-art in ultrasound imaging. Experiments using the Verasonics ultrasound scanner and simulations using Field II MATLAB package were performed for various phantoms. The results showed images of high contrast ratio and super-resolution capabilities when compared to images from traditional B-mode ultrasound. It has been experimentally verified that the UCI technique is able to achieve a spatial resolution 13 times better than the traditional US (depth of 9 cm). Lastly, an optimal ultrasound system with the resolution capabilities of the Ultrasound Coherent Imaging method and optimized hardware architecture from the proposed Compressive Ultrasound is presented. The reduced computational and hardware complexity has made this design a good candidate for future portable ultrasound systems with super-resolution capabilities."--Pages ix-x.
Recent advances in ultrafast contrast imaging have facilitated innovations such as super-resolutionimaging and ultrafast contrast-enhanced Doppler imaging (Chapter 1). It has become evident that combining ultrafast imaging with tissue harmonic imaging (THI) may offer improvements in image quality in clinical areas such as 4D THI and harmonic color flow (Chapter 1). In the first half of this work, we investigated the feasibility of combining ultrafast imaging with THI. We began with developing a numerical solution based on the Khokhlov-Zabolotskaya-Kuznetsov (KZK) to model the nonlinear propagation of sound beams produced by diagnostic arrays in tissue (Chapter 2). We then expanded our research for ultrafast THI and investigated the harmonic generation of a matrix array for identifying optimal beamforming strategies for 4D cardiac THI (Chapter 3). In the second half of this work, we proposed imaging approaches for improving tissue signal suppression and contrast sensitivity for ultrafast contrast imaging. We began with investigating the linear signal cancellation (tissue signal suppression) performance of the Verasonics research ultrasound scanner and compared it with the Philips iU22 (Chapter 4). We then studied the phase response of the microbubbles and tissue, and presented evidence that unique microbubble nonlinear dynamics can produce a phase response that can be used as a segmentation tool to further improve tissue signal suppression in contrast imaging (Chapter 5). Finally, we identified an aperture pattern for AM that improves the tissue signal suppression compared to the conventional AM. We also demonstrated that the additional phase response induced by the spatial difference between complementary half amplitude fields in OAM pulse sequences is useful for improving phase segmentation and image contrast (Chapter 6). We concluded with a summary of all the results and accomplishments and future directions of this work (Chapter 7).
Many surgeries are trending toward minimally-invasive procedures to reduce patient recovery times and produce fewer complications. These procedures are characterized by having small surgical openings, making it difficult to use medical imaging equipment not specifically designed to fit into small openings. Clinicians use laparoscopes or other optical microscopes as the primary tools for endoscopic surgeries, but these tools only provide imaging at the surface and lack depth-resolved information that would be of utmost value. Recently, a high-frequency endoscopic phased-array imaging probe has been developed which provides an unprecedented combination of depth-resolved imaging resolution with a minimally-invasive form factor (2.5 x 3.0 mm). This technology has the potential to provide enhanced image guidance capabilities to a wide array of surgical applications. To be suitable for medical imaging applications we developed a suitable electronic imaging system, commonly referred to as a beamformer, to support this imaging probe. This system was the world's first real-time beamformer for high-frequency phased array imaging and uses a newly developed variable sampling scheme termed the 'One Sample per Pixel' technique for image formation. This hardware and imaging technique generate high-quality ultrasonic images in real-time. We improved on the system's capabilities by implementing ultrafast imaging techniques that greatly increased the system's usefulness while simultaneously developing a new ultrafast imaging technique for sector imaging called sparse orthogonal diverging wave imaging (SODWI), which offers a variety of advantages over similar techniques. These capabilities were applied to functional ultrasound imaging in a preclinical setting where we were able to detect the neurological activation of auditory structures in rats, in particular, the inferior colliculus. This functional ultrasound experiment was performed through a 3.5 x 6.0 mm opening, which is smaller than any previous functional ultrasound experiments in the literature. Future directions for developing the system and new applications of these technologies are described.