March 7, 2003
E142 Research Helps Clear Stormy Lung Images
By Tom Mead
Making medical images of the interior of the body has
improved astonishingly over the last few decades. But imaging of the lungs
—getting a clear x-ray or Magnetic Resonance Imaging (MRI) picture— is
still a murky business at best. To the untrained eye, current lung images
look more like storm clouds than anything else.
Comparing the two images above shows how nuclear
medicine will benefit from noble-gas imaging. The left image shows a
scan in which a patient inhales radioactive gas and an image is made
using a gamma camera. In the image at right, the scan uses magnetic
resonance imaging (MRI) where the signal source is laser-polarized
(Images courtesy of Univ. of Virginia Radiology)
However, fundamental physics research begun in 1992 at
SLAC may soon have the unexpected benefit of dramatically improved medical
images of human lungs.
Gordon Cates, a professor in the Department of Physics,
University of Virginia, is one of three co-inventors of the medical use of
a SLAC technique for producing large volumes of polarized noble gasses.
Cates was at SLAC recently to speak about the last eight years of work on
the medical use and to point out its origins at SLAC.
As Cates explained, "Part of SLAC Experiment E142 needed
large quantities of polarized helium-3 (3He)
as a target for electrons in End Station A. However, at that time the
specialized gas could be made only in ping-pong-ball-sized quantities. The
SLAC researchers had to learn how to make basketball-sized volumes of the
gas. They did learn." And what they learned may soon be used world-wide to
produce superior medical lung images.
MRI machines ‘see’ water (actually, they see the protons
in the hydrogen nuclei in water). In the patients’ body, the intense
magnetic field produced in a MRI machine makes the protons in the water
line up like tiny compass needles turned in the direction of the magnetic
field. Since there is so little water in healthy lungs, there are few
water protons to be seen by the MRI. A readable, but fuzzy, MRI picture is
created. A way to produce better lung images was needed. Enter polarized
Laser techniques are used to make about 50 percent of the
nuclei in Helium line up in the same direction, like little bar magnets.
The 3He is about 100,000 times
more polarized than the protons that are used in conventional MRI. The
inhaled helium is less dense than water, but even so the
3He delivers an MRI-readable signal,
or image, of the gas space of the lung that is about 100X more detailed
and informative has ever been possible with conventional MRI.
The image is clearer because the 3He
defines the gas space of the lung, not because it penetrates and more
clearly defines the tissues. CAT-scan images of the lung tissue can
be quite sharp, but they provide little information about how the lung is
MRI, using laser-polarized noble gasses, has been an
expanding area of research for the last eight years. Dozens of groups
around the world have been using the technique experimentally, and
commercial applications are currently in U.S. Food and Drug Administration
The Stanford Linear Accelerator Center is
managed by Stanford University for the
US Department of Energy
Friday March 07, 2003 by