Science > Physics > PHYSICS NEWS UPDATE -- Number 848 November 27, 2007 by Phillip F.Schewe and Jason Bardi
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PHYSICS NEWS UPDATE -- Number 848 November 27, 2007 by Phillip F.Schewe and Jason Bardi |
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 848 November 27, 2007 by Phillip F. Schewe and Jason
Bardi www.aip.org/pnu
BETTER DETECTION OF THYROID CANCER 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/)
***********
PHYSICS NEWS UPDATE is a digest of physics news items
arising from physics meetings, physics journals, newspapers
and magazines, and other news sources. It is provided free
of charge as a way of broadly disseminating information
about physics and physicists. For that reason, you are free
to post it, if you like, where others can read it,
providing only that you credit AIP. Physics News Update
appears approximately once a week.
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