---------- Forwarded message ----------
Date: Tue, 26 Mar 2002 13:46:24 -0500 (EST)
From: AIP listserver <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Subject: update.582
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 582 March 26, 2002 by Phillip F. Schewe, Ben Stein,
and James Riordon
MICRO-TESLA MRI was reported at last week's APS March
meeting in Indianapolis by Robert McDermott, a member of John
Clarke's group at UC Berkeley. The principle behind MRI is
nuclear magnetic resonance (NMR), a process in which a magnetic
field (often a strong one), is used to orient atomic nuclei in space
while a burst of radio waves explores the nuclear energy levels by
charting the frequencies at which energy is absorbed resonantly. In
addition to establishing chemical identity NMR can also be turned
into an imaging method by carefully watching the timing and the
location of the re-emitted radio waves. A tumor, say, will have a
slightly different water density (as revealed, in this case, by the
presence of protons in the NMR survey) from surrounding healthy
tissue. Computer processing and contrast enhancement will
disclose the tumor's position to a trained observer. Generally large
magnets are required to produce sharp NMR images, and the
development of a low-field version would benefit medical and
scientific studies. McDermott reported an experiment in which an
array of four columns of fluid were imaged with a field of 10
micro-Tesla over the period of several hours. (See also
McDermott et al., Science 22 March 2002.)
Also at the APS meeting, Mark Haacke of the MRI Institute for
Biomedical Imaging in St. Louis (314-961-9105,
[EMAIL PROTECTED]) discussed a new MRI technique called
susceptibility weighted imaging (SWI). The technique measures
differences among brain tissue in its magnetic susceptibility,
essentially its magnetic response to the applied magnetic field of
the MRI machine. Yielding unique information from veins and
blood products, SWI has already provided more sharply detailed
MRI images of blood vessels in the brain than previously possible
and the presence of small hemorrhages in heretofore unavailable
detail. SWI can potentially detect angiogenesis, the growth of
blood vessels caused by cancer, and may improve diagnosis of
Parkinson's and Alzheimer's diseases, through its ability to monitor
iron deposits in the brain.
ELECTRICAL MEASUREMENTS OF INDIVIDUAL LIVING
CELLS
[SSZ: Text deleted]
ATOMIC FORCE MICROSCOPY YIELDS 3D PROTEIN
STRUCTURE. Despite its name, atomic force microscopy (AFM)
does not produce atomic-resolution images of proteins or other
large molecules. When imaging macromolecules, a large region,
about 100 square nanometers, of the AFM tip makes contact with
the molecule. This region is comparable in size to the entire
molecule and makes the tip a blunt probe by atomic standards. To
extract more detailed information from AFM images of
macromolecules, one can directly subtract the effects of the tip but
the results are often inaccurate. At the March APS Meeting,
Steven Eppell and Brian Todd of Case Western Reserve University
(216-368-4067, [EMAIL PROTECTED]) presented a new technique for
obtaining submolecular information about proteins. Investigating
aggrecan, a cartilage protein important in osteoarthritis, the
researchers used a technique that combined AFM with genome
information and transmission electron microscopy data. All of the
data were integrated by using a sophisticated image processing
technique to provide a best guess at the 3D structure. The resulting
refined structure yielded new information on the molecule,
showing distinct locations of kinks as well as regions of
mechanical flexibility. The researchers hope to combine their
results with AFM-measured force fields around cartilage proteins
to link the biological and mechanical properties of cartilage with
its molecular structure. This approach has the potential to provide
information on molecular-scale mechanisms for arthritis and lead
to intelligent drug design and other interventions to prevent or
alleviate the disease.
