Engineer-clinician collaborations yield innovative,
Funded via the W.H. Coulter
Translational Research Partnership in Biomedical Engineering,
these research projects recently concluded in year one of the
partnership. This partnership fosters early-stage collaborations
between University of Wisconsin biomedical engineering researchers
and practicing physicians that will enable researchers to deliver
their advances more quickly to patients.
Ultrasound waves reflect tissue mechanics
n nature, mammals such as bats and whales emit
sounds and, from the echoes that return, locate and identify objects
in their environment. In a similar manner, Professor Ray
Vanderby, Assistant Professor Lee
Kaplan (also orthopedics & rehabilitation) and Associate
Patricia Keely (also pharmacology) are
using ultrasound waves to identify mechanical properties of tissue that
might, for example, help physicians distinguish various types of cancerous
tumors. They call this noninvasive method an acoustoelastic biopsy.
They also are using ultrasound waves to determine functional tissue
loading, such as stretch in a ligament or tendon. They call this an
acoustoelastic strain gauge.
Initially, they studied reflected waves from loaded,
or stretched, and unloaded, or relaxed, tendons. When, in side-by-side
experiments, they delivered ultrasound waves to the two tendons, they
found that the reflected wave amplitude and the wave propagation velocity
were higher in the loaded, stiffer tendon than in the unloaded tendon.
From these waves, they determine material stiffness, to identify tissues
by their material properties, and strain, to measure functional loadings.
To apply this concept to orthopedics, Vanderby and
Kaplan are developing clinical protocols to diagnose rotator cuff tendon
damage, via loading patterns, and healing, via mechanical properties.
To apply the concept to tumor diagnostics, Vanderby and Keely deliver
an ultrasound signal, then palpitate, or compress the tumor. As the
tumor compresses, it becomes thinner and stiffer and the size and velocity
of the reflected ultrasound signal respond accordingly.
In laboratory tests on mouse models of the two most
common types of breast cancer tumors, they developed “signature”
ultrasound signal patterns for those tumors, reflecting their different
mechanical behaviors based only on ultrasound information. “We
can estimate the mechanical behavior quite well; we call it our stiffness
gradient index method of characterization,” says Vanderby. “But
then also we can distinguish one type of tumor from another with high
specificity and high sensitivity.”
Building on their research with isolated tissues in
the laboratory, Vanderby, Kaplan and Keely now are testing their methods