Should be attainable through a new technique being developed at the Mayo Clinic. Ultrasound is
currently the most sensitive tool for detecting thyroid nodules and
the most cost-effective imaging method for evaluating the thyroid
gland. However, the overwhelming majority of nodules discovered by
ultrasound (as high as 95 percent) are benign. Often the ultrasound
and other imaging results are ambiguous and cannot differentiate
between malignant and benign thyroid nodules. The only way to
definitively rule out a cancer diagnosis is through fine needle
aspiration and biopsy. More than half these biopsies prove benign.
While that may be reassuring to the people who undergo the biopsies,
it would be better if they could receive that reassurance without
having an expensive, invasive, and (as it turned out) unnecessary
procedure.
Azra Alizad of Mayo Clinic College of Medicine has developed a novel
non-invasive imaging technique called vibro-acoustography (VA) for
identifying thyroid nodules in excised human thyroids imbedded in
tissue gel. In this method, ultrasound is used to vibrate tissue at
low frequencies, and the resulting vibrations can be detected by a
sensitive microphone. Harder tissues normally produce a
significantly different acoustic field than softer tissues, and<
detecting the difference may reveal a more definitive diagnosis.
Malignant lesions are stiffer than benign lesions; therefore it is
reasonable to expect that VA will be a better tool for detection and
differentiation of thyroid nodules than the conventional ultrasound
imaging.
While the technique is not yet tested for actually
detecting thyroid cancers in clinical trials, vibro-acoustography is
currently undergoing clinical evaluation for detecting breast cancer
lesions in people. If successful, this inexpensive and non-invasive
imaging tool would represent a major advance in our ability to
provide care for people with potential cancer. Alizad presents his
new results this week at the meeting of the Acoustical Society of
America (ASA) in New Orleans. (Paper 3pBB3, http://www.acoustics.org/press/)
Tissue Stiffness as a Measure of a Health.
Matthew Urban (Urban.Matthew@mayo.edu) and his colleagues at the Mayo Clinic
College of Medicine are designing ways to measure the stiffness of
tissues as a non-invasive diagnostic tool. Monitoring a tissue's
material properties may not be as obvious a gauge of its health as
looking at its biological or chemical properties, but changes to
these properties can be a good indicator of disease. Areas of
stiffness in a tissue, for instance, are often a good warning sign
of cancer---the basic premise behind breast self-examination.
Likewise when cancerous tumors form on the liver or another one of
the body's organs, they are often stiffer than the surrounding
tissues because there are more blood vessels to support the tumors.
The problem is, how can you measure stiffness in tissues deep within
the body? There is no such thing as a liver self-exam. At this
week's ASA meeting, Urban reports on his latest experiments, in
which he and his colleagues used focused ultrasound waves to deliver
tiny vibrations to a steel sphere encased in gelatin, a model of a
tissue with a stiff lesion.
They were able to measure the frequency
response of the sphere to acoustical waves of multiple frequencies,
which can then be used to determine the stiffness of the
tissue-mimicking material. The method also provides new ways to
non-invasively cause vibration for assessment of tissue stiffness
without the presence of the steel sphere. Moreover, they were able
to deliver the energy to the sphere without heating the surrounding
gelatin. This is one of the challenges of using highly focused
ultrasound, because acoustical energy can be absorbed by nearby
tissues in the form of heat. (Talk 3pBB1, meeting website:
http://www.acoustics.org/press/)
Recreating the World Inside Your Head
The first use of individualized virtual-reality sounds in a functional MRI (fMRI)
environment to reproduce a naturalistic acoustic experience for
studying brain function might provide a better explanation of the
"cocktail party" effect-the process by which we try to make sense of
a conversation at a crowded party even as several other potentially
distracting conversations proceed at the same time. New brain scans
using fMRI are helping researchers to understand how the brain
segregates objects in space when a person hears, but not necessarily
sees, multiple sources of sound. At Kourosh Saberi's
(saberi@uci.edu) lab at the University of California, Irvine, human
subjects are exposed to several sounds.
Sometimes the sounds come
from different locations near the subject, while sometimes several
sounds come from a single location. When looking at fMRI scans
showing areas of enhanced blood flow, which provides 2-mm-resolution
maps of brain activity, the U.C. Irvine scientists report two main
results. First, no specific brain region accounts exclusively for
identifying auditory motion, in contrast to the visual cortex which
does have specific motion-sensing regions. And second, spatial
auditory information seems to be processed in a neural region,
called the Planum Temporale, in a way that can facilitate the
segregation of multiple sound sources. (ASA meeting talk 2aPP8,< http://www.acoustics.org/press/)
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