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At the end of this course, you will know how an ultrasound image is formed, from the signal generation to the image, passing by the transducer, the wave interaction with soft tissue, the required signal processing and the utilization of a medical scanner.
This course is not a medical course and therefore does not aim at simply showing how to operate an ultrasound scanner or perform a diagnostic examination. We aim at providing you with an in-depth understanding of the imaging process in order to give you the base required to go towards research, industry, or clinical physics. The primary aim of this course is therefore to explain the in and out of ultrasound imaging. This includes the basic physics of ultrasound propagation and scattering, the working principles of a transducer and the basics of signal acquisition and processing that lead to a greyscale image. Additionally, new techniques like contrast imaging using microbubbles and functional imaging including strain and shear wave imaging will be discussed. Building on this, we will discuss the differences between the different imaging modes in ultrasound both implemented in the clinics and under development.
Overall, you are expected to explain your reasoning, in a concise but complete way. When a small derivation is required, we expect to see this derivation in its main steps. Extensive answers where the correct response is provided together with wrong elements will typically not give the full points.
During the exam, no document or computer are allowed, and only a non-programmable calculator will be allowed. The grade repartition is: exam 50%, homework, 25% and lab reports: 25%. A minimum of 5.5 at the exam is necessary to validate the course.
When acquiring an ultrasound image, all the acoustic phenomena, and processing techniques occur simultaneously, in a way that makes them difficult to isolate. The lectures are designed to address each aspect independently and explain how they interact in an ultrasound image acquisition. The homework assignments will reflect the lectures and require from You to manipulate and crystalize the concepts through exercises. These exercises will train the various important skills that you are expected to develop, and in particular the use of Matlab, basic programming skills, knowledge of the basic operations and transforms, and their implementations. The tutorials will offer supervised exercises to start manipulating the lectures concepts during 2 dedicated hours per week. The tutorials will also leave room for question regarding the lectures, previous exercises, or practicals. The practicals will show how to apply the concepts from the lectures and homeworks. The first practical will consist of a hand-on training in the ECTM on clinical ultrasound scanners and training simulators in order to provide context. Subsequently, you will use single element transducers to send and acquire the signals and observe the various acoustic phenomena that give rise to scatter, reflections, attenuation and distortions.
Prerequisite
You are assumed to master basic mathematical concepts, such as:
- the use of a log and an exponential function,
- the difference between natural log and decimal log,
- basic integrals,
- linearization of the basic function (e.g.: sin(x) ≈ x for x ≈ 0).
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Lecture 1: course introduction and basics of signal processing useful for medical acoustics (Guillaume)
Content:
Course introduction
Formulate the goal of the course
Course concept: why we need to pass by all these elements (= 8 lectures)?
What will you learn?
- Signals
- Fourier transform and fft
- Fourier filtering
- Bandwidth VS signal duration
- Interpolation
- Cross-correlation
- Hilbert transform
- SVD filtering
- List of useful matlab/python functions
What you get out of the colstructure:
At the end of this first course and associated tutorial/homework,
- You understand the logic in the construction of the course and see how the pieces fit together as a whole. You can explain why each part is necessary to be able to create an ultrasound image.
- You can use the basic processing functions essential to ultrasound imaging. You can explain what they are used for and why.
- You can practically implement these functions in Matlab and have a library of the essential Matlab function that you will use throughout the course (and beyond, as these functions are widely used).
Lecture 2: ultrasound (physics) (Guillaume)
Content:
- Wave: the different waves, definition, frequencies and dispersion relation
- Wave equation
- Acoustic impedance
- Intensity VS pressure
- Reflection, transmission, refraction
- Attenuation
- Scattering (the different types of scattering)
- Non-linear propagation
What you get out of the colstructure:
- After this lecture, you can distinguish between the types of wave, and know which waves are used in medical ultrasound.
- You know the relation dispersion that characterizes acoustic waves and the difference between pressure and intensity (This is a critical point).
- You understand which tissue/material properties are important for ultrasound and what their impact is on ultrasound propagation.
- You understand the origin of reflection and scattering and explain the difference. You can manipulate the basic relations that describe the reflection or transmission of a wave across an interface.
- You can explain the difference between the linear and non-linear effects, and know the impact of the non-linear effects on the ultrasound wave, both in time and in the Fourier domain.
Lecture 3: transducers (Michel)
Content:
- Single element transducers
- The main characteristics (what you read on it: frequency, diameter, focal distance, etc…)
- Focused and unfocused transducers
- Near and far field
- The different transducer arrays
- The different transducer type and the working principles
- Piezos:
Piezo ceramics
Piezo polymers
Cmut
Pmut
- Matching layers and acoustic lenses
What you get out of the colstructure:
- After this lecture, you can explain the technologies used in transducer to emit and receive waves. You can explain what the differences are between the technologies and describe their field of application.
- You understand how clinical probes (arrays) are made, their composition and the role of the different structural elements. You can reason based on the superposition of the sources that are each of the elements. You can give an overview of the resulting specific artifacts present in clinical scanners.
Lecture 4: beamforming (Chris)
Content:
- Beamforming in emission
- Plane-wave VS traditional B-mode (multibeam)
- System resolution
- Effect of pulse length
- Delay/sum for image reconstruction
- Beamforming in receive/ synthetic aperture
What you get out of the colstructure:
- You can use an array to produce any wave shape that might be needed in ultrasound imaging.
- You can explain the difference between the standard B-mode imaging and plane-wave imaging and you understand the concept of each and the advantages and inconvenient of both.
- You know and can explain the physical resolution of the systems, both in the axial and in the lateral directions and how in changes with frequency and with the choice of the probe.
- You can perform the basic delay/sum technique for reconstructing an ultrasound images from the RF time series recorded by the transducer elements.
- You can explain the concept of beamforming in receive and of synthetic aperture and understand how they can improve image reconstruction.
Lecture 5: Ultrasound contrast agents (Michel)
Content:
- Bubble physics
- Imaging schemes with bubbles
What you get out of the colstructure:
- You can explain what ultrasound contrast agents are, and what they consist of.
- You understand the basic properties of non-linear bubble behavior and can identify them on typical bubble signals.
- You understand the composition of the bubble shell and its impact on bubble dynamics.
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Lecture 6: flow imaging techniques (Chris)
Content:
CW Doppler
Pulsed Doppler
X-imaging
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Speckle tracking
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Vector flow imaging
What you get out of the colstructure:
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You can explain the difference between pulse and CW Doppler.
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You can use the concept of Doppler and Doppler imaging and the basic Doppler relations to calculate velocities.
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You know when Doppler is used in the clinic, can explain its importance for flow imaging and its limitations.
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You can give an overview or the different flow imaging techniques and the compromises to make when using them.
Lecture 7: elastography techniques (Chris)
Content:
- Strain imaging from induced deformations
Concept
Implementation
Example
Concept
Implementation
Example
Concept
Implementation
Example
What you get out of the colstructure:
- You understand the difference between a shear wave and an ultrasound wave. You can give the differences in their intrinsic properties and their dependency on tissue properties.
- You can justify the large speed differences of a compression and of a shear wave in tissue, enabling the concept of shear wave imaging.
- You know how to generate a shear wave in practice or how to make use of shear waves naturally occurring.
- You can explain the concept of speckle tracking elastography and the fundamental differences with shear wave imaging.
Lecture 8: Complements (Guillaume)
Content:
- The different types of scanners
- IVUS
- Lithotripsy/histotripsy/thrombolysis
- Therapeutic ultrasound
- Superresolution imaging
- Time reversal acoustics
Thermal/mechanical ablation
Local drug delivery with bubbles
BBB opening
Immunotherapy
What you get out of the colstructure:+
The course does not aim at (and could not be) exhaustive on all the ultrasound techniques in use or in development. This last course aims at giving an overview of the topic that were not treated in the course, and the state of the art of some important research topics in ultrasound. You can then explain the basic idea behind each of these complements and their biomedical interest.
LAB COURSES
Week 1: Hands on ultrasound training at the ETCM.
The first lab course consists in a hands-on training in the ECTM in the Techmed center. During this training, the student will learn how to use a clinical ultrasound scanner. You can familiarize with the system, the transducer, ultrasound images. You manipulate the machine that embeds all the components you will study in the course.
Week 2: Basics
During this practical, you familiarize with the basics components and electronics associated with the use of single element transducer that you will use throughout the practical session. you will recall how to setup and use an oscilloscope, you learn what a pulser-receiver is, and how to use it. In addition, you get the chance to think about the functionalities and limitations of the various devices, in particular in terms of clipping. You perform initial measurements by sending a wave to a flat plate and measuring the reflected echo.
Week 3: Speed of sound, acoustic impedance and attenuation
In the second session, you manipulate the ad practically measure the concepts of acoustic impedance, transmission and reflection at interfaces, and the relation between pressure and energy. The use the different concepts and formulas learned in the lectures and tutorials to measure material properties. In this session, you also approach in a simple, frequency-independent way the attenuation through a set of materials as a preparation for the following week.
Week 4: Frequency domain
In the lectures and homework, extensive attention is brought onto the frequency content and the relation between the frequency and the time domain. This concept is essential to ultrasound imaging. Building up on week three, you will focus on measuring and analyzing the frequency content of ultrasound pulses and the effect of e.g. attenuation on it.
Week 5: Non-linearity and beam profiles
Now that you are familiar with the concept of frequency domain and with the fact that it can be affected by physical phenomena such as attenuation, you will look at a more complex effect, yet a critical one in practice: nonlinear propagation. You will experimentally investigate how nonlinear propagation evolves with pressure, propagation distance and frequency.
Week 6: Doppler
In this penultimate practical, you will touch upon the concepts of motion and flow. More specifically, you will implement time-of-flight doppler measurements experimentally and analyze the data to recover the speed of circulating bubbles.
Week 7: Imaging
In this last practical, you will implement the ensemble of the knowledge gained in the course as you attempt to acquire and reconstruct an ultrasound image of an unknown, opaque phantom.
Purpose
In-depth knowledge of the working principles and applications of medical ultrasound.
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| | Required materials-Recommended materialsCourse material| Lecture slides. Homework and simulation assignments. Practical session manual. Book: Diagnostic Ultrasound Imaging - Szabo. All digitally available through Canvas. |
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Instructional modesLab Course| Presence duty | | Yes |
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TestsExam
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