Page 38 - Summer2019

From Biology to Bytes: Predicting
the Path of Ultrasound Waves Through
the Human Body
Bradley E. Treeby Computer simulations are increasingly used to guide ultrasound therapies, but
Addms: what makes a good model and when can we trust them.’
Department ofMedical Physics and
Biomedical Engineering '""°‘“°“°"
University Couege Land“ The use of ultrasound as a diagnostic imaging tool is well-known, particularly
Gower Sue“ during pregnancy where ultrasound is used to create pictures of developing babies.
Landon WCIE 531- in recent years, a growing number of therapeutic applications of ultrasound have
Ulmed Kmgdnm also been demonstrated. The goal of therapeutic ultrasound is to modify the func-
‘ tion or structure of biological tissue in some way rather than produce an anatomical
Emmi: image. This is possible because the mechanical vibrations caused by ultrasound
b'“eeby@“d‘aC'“k waves can affect tissue in different ways, for example, by causing the tissue to heat up
or by generating internal forces that can agitate the cells or tissue scaffolding. These
Iiri Jams ultrasound bioetfects offer enormous potential to develop new ways to treat major
Address: diseases. In the last few years, clinical trials of difierent ultrasound therapies have
Centre Of Excellence IT4J_n_nOva‘_im“ demonstrated the ability of ultrasound to destroy cells through rapid heating for
Faculty of Information Technology the treatment of cancer and neurological disorders, target the delivery of anticancer
Brno Univemty of Tedmohgy drugs, stimulate or modulate the excitability of neurons, and temporarily open the
Bozflechova 2 blood-brain barrier to allow drugs to be delivered more effectively (Konofagou,
612 56 Brno 2017). These treatments are all completely noninvasive and have the potential to
Czech Republic significantly improve patient outcomes.
_ __ Emmi: The fundamental challenge shared by all applications of therapeutic ultrasound
’ams)u@fi”utb”Cz is that the ultrasound energy must be delivered accurately, safely, and noninva-
sively to the target region within the body identified by the doctor. This is difficult
Eleanor Martin because bones and other tissue interfaces can severely distort the shape of the
Emmi, ultrasound beam (see Figure 1, bottom, for an example). This distortion can have
Euy_marfin@ud_aC_uk a significant impact on the safety and effectiveness of therapeutic ultrasound
and is one of the major hurdles for the wider clinical acceptance of this exciting
Ben T. Cox technology. In principle, it is possible to predict and correct for these distortions
Emmi, using models of how ultrasound waves travel through the body. However, the
b_C°x@ud_aC_uk underlying physics is complex and typically must consider nonlinear wave propa-
Address: gation through absorbing media with ‘spatially varying material properties. Simple
De amnem ufMEdjcal Pk _ d formulas do not exist for this scenario, so models used for studying therapeutic
P _ y_s";s ultrasound are instead based on the numerical solution of the wave equation (or
Biomedical Engmeumg the corresponding constitutive equations). This article is primarily concerned
University Collage Land” with the development of such models.
Gower Street
L°““"“ WCIE 5“ Circle of Model Development
Unned Kingdom One way to consider the development of numerical ultrasound models, and indeed
any scientific software that models a physical phenomenon, is described by the circle
of model development (see Figure 2). This has five distinct components:
as | Anal.-H:-Tbrluy | Sunu-ner 2019 | volume 15, issuez ©2o19Acou.m:nl Society afArnerxra. All rights reserved.
htlps://doi.oi'g,/l0.l121/AT.3Ul‘l.l5.l 36