Speakers: Koen van Dongen

To design and build your own imaging or full-waveform inversion method, it is important to have a good and solid understanding of the mechanism underlying the propagation – including scattering, refraction, diffraction, etc – of acoustic wave fields in heterogeneous media. Consequently, we will start our course by a derivation of the acoustic field equations (equation of motion and equation of deformation) using simple laws from mechanics. We will show that the acoustic wave field composes of a pressure and a velocity wave field, and that linearized versions of the field equations are used to derive the wave equation for linear acoustics. A similar approach is used to derive the Westerveld equation for non-linear acoustics. Subsequently, we will discuss different solution strategies for modelling acoustic wave fields in heterogeneous media, as well as the concepts behind Kirchhoff Integrals, Rayleigh I and II, and evanescent waves. Finally, we combine all these concepts to explain the theory behind imaging and (non-linear) full-waveform inversion for quantitative ultrasound imaging.

Speakers: Andreas Mayer

Nonlinearity in the context of ultrasonic waves has gained increasing attention in recent years for various reasons. In micro-acoustic devices for mobile communication, nonlinear effects can lead to signal corruption and require countermeasures, especially in view of tightening linearity requirements by new standards like 5G. In the field of non-destructive evaluation, nonlinearity is a desired effect, as it provides a better chance to detect, with the help of ultrasound, defects and pre-fatigue at an earlier stage as compared to the linear regime. Nonlinear effects have to be well understood for their efficient use or design of countermeasures.

This short course will start with a brief explanation of the physical origin of classical (electro-)elastic nonlinearity which manifests itself in high-rank tensors of material constants. They occur in higher-order terms in an expansion of the potential energy density in powers of strain and electric field components. In addition, certain sources of “non-classical” nonlinearity will be addressed like micro-cracks and other types of defects. A brief introduction to the theory of electro-elasticity will be given and its application to various types of guided waves with focus on surface acoustic waves. Among the dynamic nonlinear effects covered in the course are harmonic generation and nonlinear mixing, e.g. intermodulation, influence of nonlinearity on resonance curve and phase response of SAW resonators, nonlinear Cherenkov radiation, nonlinear waveform evolution and solitary waves. For some of these effects it will be shown how they can be modeled and analyzed within perturbation theory, including asymptotic expansions. This approach can be combined with other modelling tools like the finite element method.

Speakers: Ruud JG Van Sloun, Yonina Eldar

Over the past years, deep learning has established itself as a powerful tool across a broad spectrum of domains. While deep neural networks initially found applications in the computer vision community, they have quickly spread over medical imaging applications, ranging from image analysis and interpretation to – more recently – image formation and reconstruction. Deep learning is currently also rapidly gaining attention in the ultrasound community. This course will first cover the basic principles of deep learning, ranging from understanding the relevance of sequential nonlinear transformations for representation learning to log-likelihood based optimization of neural network parameters. Optimization aspects such as the impact of local minima and saddle points in the solution space will also be touched upon. We will then discuss the design of effective neural network architectures, including dedicated solutions that e.g. leverage signal structure through unfolding methods. The second part will focus on the wealth of opportunities that deep learning brings for ultrasound imaging. Beyond image-level classification and segmentation, we will discuss neural networks for front-end receive processing, including beamforming, clutter suppression, and advanced applications such as super-resolution imaging.

Speakers: Peter Kackowski, Thomas Szabo

This introductory course is intended to give students and those newly entering the field of ultrasound imaging an overview of medical ultrasound. We provide a framework for introducing the concepts of how an ultrasound system images the body and how it can be applied to different applications. First, we present how tissues interact with sound waves through a series of simulators. Second, we follow signals through an imaging system as they turn from electrical pulses in a beamformer and transducer into acoustic waves and back into electrical signals and finally into an image. Third , we demonstrate different types of imaging modes and their role in the visualization of three-dimensional objects. Fourth, we explain how an ultrasound research system can be reconfigured to serve different functions and applications. Finally we provide a brief overview of the different branches and specialized applications of ultrasound. Throughout the course, we demonstrate the principles by using special purpose interactive computer simulators as well as live experiments and imaging with an ultrasound research system.

Speakers: Yook-Kong Yong

Today’s precision piezoelectric acoustic wave devices require many common features such as high Q, low power, small size, and stringent requirements on frequency stability, temperature stability, and force sensitivity. Since the devices are employed as elements of frequency standards and detection, their frequency performances have to be maintained by precision designs, manufacturing, and operations. Consequently, the analysis and design of these piezoelectric devices would need 2-D or 3-D models that are accurate in terms of the resonator geometry, mountings and material properties. Furthermore, we would also need models for nonlinear analysis that include effects such as (1) temperature sensitivity, (2) applied forces from environmental vibrations, (3) harmonic generation, and (4) intermodulation. These models are useful for design and analysis of acoustic resonators because we have been successful in extracting their electrical circuit parameters and identifying the major factors impacting their precision frequency performances. The course will first focus on the primary aspects of accurate linear finite element modeling, such as the frequency spectra and quality factor Q as functions of resonator geometry and mountings. Comparisons of model results with the relevant experimental results are presented. Next the nonlinear finite element modeling of these devices are discussed. Both linear and nonlinear material properties and deformations are taken into account. The linear and nonlinear material constants for common piezoelectric materials are discussed and presented. The nonlinear behavior of quartz resonators such as their frequency-temperature behavior, force-frequency effects, and nonlinear resonance including the Duffing effect will be presented. If time permits, nonlinear frequency response modelling for force frequency effects, harmonic generation and intermodulation of BAW and SAW resonators will be presented and compared to experimental results.

Speakers: Ji Wang

With the rapid miniaturization of acoustic wave resonators for frequency control and sensor applications, the analysis and design of acoustic wave resonators are moving toward computer-based process with strong demands on formulation and modeling with the consideration of materials and dynamic features. In responding to heavy dependence on design tools, it is important to start with the fundamental theories of acoustic wave devices to support numerical analysis. We present the basic equations of wave propagation in piezoelectric solids with emphasis on device structures, crystal materials, plates, films, and layered structures corresponding to their vibration modes and frequencies. Simplifications are made to typical resonators for their distinctive frequencies in relation to the functioning modes. These results are important in guiding the inception and development of newer types of resonators. Further improvements of analysis can be done along this line by utilizing numerical methods for accurate solutions of vibration modes and frequencies of actual resonator structures for optimization to achieve better performance and accurate extraction of electrical parameters for circuit design. The formulation and methods can be applied to common types of resonators such as quartz crystal resonators (BAW), surface acoustic wave resonators (SAW), and film bulk acoustic wave resonators (FBAR). Eventually, a formal procedure of the complete formulation and approximate analysis of acoustic wave resonators will be presented and discussed. This course is considered as the introduction of the formulation and analysis of performance properties of acoustic wave resonators, and further engineering solutions can be acquired with the help of practical tools such as finite element analysis.

Speakers: Billy Yiu, Marcin Lewandowski

Nowadays, GPUs (Graphics Processing Units) serve as work-horses for processing massive amount of data and to accelerate general-purpose scientific and engineering computing. 

The main goal of the training is to get familiar with the GPU/parallel programming and apply it to ultrasound signal processing. The short-course is going to be practically oriented with a 50/50 split between the lectures and exercises. We are planning to leverage a common knowledge of the basic ultrasound processing methods and show how to translate them into working parallel algorithms. 

The workshop will target both low-level Nvidia CUDA GPU programming and high-level Python tools. This blend of development tools enable fast prototyping of new processing methods and later migration to a high-performance native GPU implementation.

During the exercises, the Participants will implement and test their algorithms on ready to use RF datasets, as well as have an opportunity to run them on an ultrasound research system equipped with GPU.

Speakers: Erdal Oruklu, Jafar Saniie

In this short course, we present machine learning and signal processing algorithms for ultrasonic imaging applications. This course covers several case studies such as detecting defects in critical components used in nuclear power plants, pulse-echo chirplet estimation, flaw detection in large-grained materials using order statistics and deep artificial neural networks, ultrasonic data compression using machine learning, software-defined ultrasonic system design for communication through solid structures, and hardware/software codesign using system-on-chip for ultrasonic signal processing applications.

Speakers: David Mills, Scott Smith

Ultrasound has become the most commonly performed medical imaging procedure in the world because it provides real-time imaging with high clinical value while being portable, non-ionizing and inexpensive. This course will provide an introductory survey of ultrasound imaging focused on the design, fabrication, and testing of medical ultrasound transducers.  Starting from an overview of the basic types of phased-array transducers (linear, convex, sector), we will show how the probe’s design is derived from its target application.  We will describe how engineering tools, like equivalent-circuit, finite-element, and acoustic field models, can be used to predict transducer performance accurately, and then to optimize the design.  A discussion of the structure of an ultrasound probe will lead to a survey of the different types of materials used in probes and their critical properties.  Typical fabrication processes will be reviewed and common problems in probe manufacturing will be summarized.  Methods for evaluating completed transducers will be described.  The course will include recent developments in probe technology, including single crystal piezoelectrics, cMUT transducers, catheters, 2D arrays, and electronics in probes, and will address some of the performance advantages and fabrication difficulties associated with them.

Speakers: Sandy Cochran, Susan Trolier-McKinstry

Piezoelectric ultrasound transducers are ubiquitous in contemporary ultrasound systems, with applications including biomedical therapy and imaging, nondestructive evaluation, and underwater sonar. This course provides a foundation of understanding of the fundamentals of piezoelectric materials and their use in ultrasound transducers, and an informed appreciation of more advanced subjects in the state of the art.

Piezoelectric single crystals, ceramics, and thin films are introduced, along with mathematical descriptions of them and their behavior and an explanation of the underlying physics. The nature of different materials is described, with particular reference to the phase diagrams, domain structures, and the resulting impact on properties. Comparisons will be made between single crystals and ceramics, with an emphasis on the impact on parameters essential for ultrasound generators and receivers.

The operating principles of transducers based on piezoelectric materials are described with reference to wave propagation within and external to the transducer. Electrical impedance spectroscopy is introduced for both material characterization and transducer performance prediction, with emerging characterization techniques and virtual prototyping highlighted.

Ultrasound transmission and reception techniques are considered, and these will be linked with modelling, through descriptions of one-dimensional models and a summary of the capabilities of finite element analysis. The effects of different piezoelectric materials are demonstrated with simplified transducer configurations and the selection of materials for specific applications are considered in detail.

Throughout the course, practical examples and modeling are used to illustrate the concepts under discussion, established and new piezoelectric materials, characterization and analysis, and how piezoelectric components affect transducer behavior.

Speakers: Sunil Bhave

In this tutorial I will present architectures based on piezoMEMS technology to demonstrate stress-optical modulation and tuning of silicon nitride and silicon photonic integrated circuits. We will define fundamental performance metrics and compare various monolithic and heterogeneous optomechanical systems. In the second part of the course, I will introduce new applications enabled by optomechanics including acousto-optic modulators, inertial sensors, magnetic-free optical isolators, and fast tunable lasers for LIDAR and microcombs. I will then close with a discussion of applications of ultrasonic piezoMEMS technology and frequency control not only of photons (flying qubits) but also color centers in diamond and silicon carbide (atom-like defects).

Speakers: Olivier Couture, Vincent Hingot

Super-resolution imaging has the capacity to distinguish and map structures that are smaller than the classical limit, typically a fraction of the wavelength. For ultrasound imaging, this means exploring features, such as blood vessels, in the micrometric range deep inside tissue. At the end of this course, students should be able to understand and reproduce super-resolution ultrasound imaging experiments, from data acquisition to image reconstruction, and apply such knowledge in their specific fields. We first explore the fundamental aspects of imaging resolution in ultrasound. Various approaches to bypass the diffraction-limit with microbubbles and other agents are presented. More particularly, we discuss ultrasound localization microscopy, which has recently improved the resolution for vascular imaging by more than 10-fold. We present its various steps, including separation, localization and tracking, and compare different approaches. Specific elements such as temporal resolution, motion correction or volumetric imaging are considered. We then detail the applications of super-resolution ultrasound for brain, tumor, kidney, liver lymph nodes and peripheral vessels imaging, along with future perspectives in the clinical and preclinical context. The last part of the course will include hands-on image processing of in-silico and in-vivo open data with provided ultrasound localization microscopy algorithms.

Speakers: David Melodelima, Meaghan O’Reilly

This short course gives an introduction to therapeutic use of ultrasound that is currently transitioning from research studies to clinical practice. The ultrasound induced bio-effects useful for therapy will be reviewed along with the generation of ultrasound. Mainly the absorption of ultrasound waves in soft biological tissues leading to heat creation will be described as well as the concept of the equivalent time at 43°C. The second half of the course will cover mechanical effects of ultrasound, and will discuss non-thermal therapy approaches, including lithotripsy, histotripsy, non-thermal ablation and targeted drug delivery. The potential of therapeutic methods using ultrasound currently in preclinical evaluation and clinical practice will be discussed together with the future directions and potential impact of therapeutic ultrasound. The course will emphasize technological issues and system architecture constraints, and will cover the current therapy ultrasound systems and their use in clinical practice. Examples of the results of the clinical studies will be reviewed.

Speakers: Mickael Tanter

The advent of ultrafast ultrasonic scanners is paving today the way to tremendous applications in medical Ultrasound. This course will present the basic principles of Ultrafast Imaging (plane or diverging wave imaging, parallel receive beamforming, coherent plane wave compounding, …) and their implications in terms of resolution, contrast and frame rates. It will also explain the analogy such concept with optical holography. For our purposes, theoretical aspects and experimental validations will be highlighted. The course will also emphasize technological issues and system architecture constraints. Far beyond breaking technological barriers, this concept of ultrafast imaging is currently changing the paradigm of ultrasound imaging. The course will illustrate how this concept leads to breakthrough innovations in the field by revisiting Bmode, Doppler, tissue strain and nonlinear imaging. Many examples (Shear Wave Imaging, Ultrafast Doppler, fUltrasound, Ultrafast Contrast Imaging, ultrafast Ultrasound Localization Microscopy,…) will illustrate the potential of this paradigm shift in ultrasound imaging.