TUTORIAL AND PLENARY OUTLINE

Circuitocultural

Informations

• Publié par: Urzoe
• Nombre de lectures: 35
• Langue: English

Extrait

TUTORIAL AND PLENARY OUTLINE

Professor LeifBjørnø:

Introduction to Nonlinear Ultrasonics A brief review of the basic principles

of fluid mechanics needed for development of linear and nonlinear ultrasonic concepts will be

given. The basic principles of linear ultrasonics will be discussed including velocity of sound,

attenuation, relaxation etc. The fundamental equations of nonlinear ultrasonics (NLU) will be

derived and their physical properties explained. It will be shown how an originally

monochromaticfinite-amplitude ultrasonic wave, due to nonlinear effects, will distort during its

propagation in time and space to form higher harmonics to its fundamental frequency. The

concepts of shock formation will be presented and [WINDOWS-1252?] its “mechanisms” based on

material and convective nonlinearity will be illuminated. The material nonlinearity, described by

the nonlinearity parameter B/A of the material, and the convective nonlinearity, described by the

ultrasonic MachNumber, will be explained and their significance in nonlinear ultrasonics will be

illuminated. Two procedures for determination of B/A, the thermodynamic and the finite-

amplitude procedures, will briefly be described and some B/A-values characterizing biological

materials will be presented. Shock formation described by use of the Goldberg Number will be

introduced, and the importance of this number and the concept of Ultrasonic Saturation will be

discussed. It will be shown how, prior to shock formation, the harmonic components of unfocused

finite-amplitude ultrasonic waves will have different directivity functions (beam patterns), with

higher directivity for higher harmonics, which can be used to improve resolution in image

formation. An introduction to focused ultrasonic fields will be given and it will be shown how the

ultrasonic intensity will vary axially and laterally in the focal region and how the field parameters

of interest to biomedical applications may be described by use of the KZK-Model. These focusing

effects have been used in lithotripters, in ultrasonic surgery and in ultrasonic microscopes.

Finally, an introduction will be given to the mixing and interaction of two monochromatic, finite-

amplitude ultrasonic waves in a liquid, for instance leading to the so-called [WINDOWS-1252?]

“Parametric Array”, and the potentials of this mixing process in biomedical ultrasound will briefly

be mentioned.

Peter A. Lewin:

Nonlinear Acoustics in Ultrasound Metrology and other selected applications

Asuccinct background explaining why, initially, the scientists and industry were skeptical about

the existence of the nonlinear (NL) wave propagation in tissue will be given and the design of an

adequately wideband piezoelectric polymerhydrophone probe that was eventually used to verify

that the 1-5 MHz probing wave then used in diagnostic ultrasound imaging was undergoing

nonlineardistortion and generated harmonics in tissue will be discussed. Thefar-reaching

implications of the advent of the piezoelectric PVDF polymermaterial will be reviewed and the

advances in ultrasound metrology prompted bythe regulatory agencies such as US Food and Drug

Administration (FDA) and International Electrotechnical Commission (IEC) will be presented.

These advances include the development of absolute calibration techniques forhydrophones along

with the methods of accounting for spatial averaging corrections up to 100 MHz and the

development of "point-receiver" hydrophone probes utilizing acousto-optic sensors. Next, selected

therapeutic applications of nonlinear ultrasonics (NLU), including lithotripters will bebriefly

discussed. Also, the use of shock waves as pain relief tool and inabating penicillin resistant

bacteria that develop rock hard "biofilm" that can be shattered by the finite amplitude wave will

also be mentioned. The growing applications of NLU in cosmetic industry where it is used for

liquefying andredistribution of fatty tissue within the body will be briefly reviewed, and, finally,

selected examples of NLU applications in retail and entertainment industry will also be pointed

out.

Professor Andrzej Nowicki:

Nonlinear Acoustics in Medical Ultrasonics The new imaging

modalities of ultrasound diagnostic machines that utilize nonlinear (NL) acoustic or ultrasound

wave propagation in issue will be reviewed. These include tissue harmonic imaging (THI),

PulseInversion (PI), and enhanced detection of microbubbles being used as contrastagents (CA).

The clinical examples oftheir applications will be presented and the potential of nonlinear

ultrasonics(NLU) in clinical practice will be discussed. The role of theoretical NLpropagation

models in enhancement of image quality will also be examined and anovel imaging scheme that

utilizes nonlinear properties of tissue to improve contrast to noise ratio will be introduced. This

scheme makes use of theacoustic source that is activated by two tone bursts having variable

polarization. This new approach is termed multi-tone nonlinear coding MNC because the choice of

polarization of both tones (and their amplitudes) allows optimization of the receiving properties

yet depends on the nonlinear properties of tissue. The concept of the virtual fields will be

introduced to explain abilities and properties of the PI and MNC imaging and to facilitate the

comparison of these two methods. The comparison of the spatial field distribution achieved using

the MNC approach with the conventional harmonic imaging one, in which the second harmonic is

used to reconstruct the image shows that for the same peak pressure amplitude the resulting

Mechanical Indexfor MNC may be lowered by almost 40% in comparison with that achievable

using the Pulse Inversion approach.

Lawrence Crum

. Ultrasound Therapy: New Trends and Future Applications. Ultrasound has

become one of the most widely used imaging modalities in medicine; yet, before ultrasound-

imaging systems became available, high intensity ultrasound was used to ablate regions in the

brains of human patients. Recently, a variety of novel applications of ultrasound has been

developed that include site-specific and ultrasound-mediated drug delivery, acoustocautery,

lipoplasty, histotripsy, tissue regeneration, ultrasound-triggered auto-immune response, and

bloodless surgery, among many others. This lecture will review several new applications of

therapeutic ultrasound and address some of the basic scientific questions and future challenges in

developing these methods and technologies for general use in our society. We shall particularly

emphasize the use of High Intensity Focused Ultrasound (HIFU) in the treatment of benign and

malignant

tumors.

Jens E. Wilhjelm

. Teaching Medical Imaging: Seeing Biological Tissue with Ultrasound, MRI, CT

and Your Eyes. The research field of medical imaging, and thereby also ultrasonic imaging, relies

- as all research fields - on new researchers entering the playground. This requires continuous

exposure of the field as well as academic training. In these contexts, we have in the past five

years conducted a course in medical imaging within the framework of the education Medicine and

Technology, a joint biomedical engineering education between the Faculty of Health Sciences,

University of Copenhagen and the Technical University of Denmark (DTU). The DTU course

Introduction to medical imaging introduces ultrasound, CT, MRI, PET and planar X-ray to the

students through lectures, interactive demonstration programs as well as project work involving

hands-on imaging of phantoms with subsequent image processing and analysis. Within the latter,

teams of students are given a phantom with unknown tissue and this is then scanned with the

techniques taught in the course (at hospitals and at DTU). All scannings are conducted with

clinical equipment and performed in 3D including ultrasound which is recorded by automatically

moving the transducer across the phantom in a water tank. The phantoms consist of formalin

fixed animal tissue embedded in agar with fiducial markers for image alignment. The images are

then analyzed by the students so that they can compare the same scan plane with all techniques.

The tissue is then attempted identified, but in order to do that, the students need to understand

the physical principles of the imaging techniques. Later, the tissue is sliced and photographed

(with a flat bed scanner) in order to provide a golden standard. This talk will shortly introduce the

components of the course followed by a short outline of the physical principles of the imaging

techniques, partly with interactive demonstration programs. Examples of comparative images -

from the same scan plane - are then given for various kinds of animal organs and tissues as well

as string phantoms. This gives the opportunity to study and compare differences in contrast,

point spread function and the like for all the techniques. Results of the course show high increase

in competences as judged from graded reports, low course dropout rate, high pass-rate at the

exam, high student participation and large student satisfaction.