imaging (MRI)—a widely used medical tool that relies on magnetic fields
and radio waves to visualize the body’s internal structures, especially
soft tissues—may soon become even more useful.
The National Institute of Standards and
Technology (NIST) has unveiled the first “phantom” for calibrating MRI
machines that is traceable to standardized values. The prototype, named
Phannie, was developed in collaboration with the standards committee of
the International Society for Magnetic Resonance in Medicine (ISMRM).
Traceable MRI calibrations are expected to
enable accurate, quantitative measurements of tumors and other disease
markers that can be reproduced across many different patients, scanners
and clinics over time—and potentially reduce medical costs.
Displayed at the annual ISMRM meeting this
past week,* the NIST phantom is a plastic sphere about the size of a
person’s head, filled with water-bathed grids of 100 small plastic
spheres containing various salt solutions that become magnetized in a
magnetic field. By making MRI scans of Phannie, users can evaluate the
image contrast, resolution, and accuracy of distance and volume
measurements. A machine’s performance can be compared to standards, to
other MRI machines, and to itself over time.
MRI scanner performance may drift, or
different machines may produce different images of the same patient. The
new phantom is intended to help generate more accurate and consistent
images, help validate disease mechanisms and treatments, and reduce
medical costs by improving image quality and reliability. The phantom
will assist multisite clinical trials that use quantitative MRI to test
the efficacy of novel drugs.
A number of specialized MRI phantoms already
exist; the need for new ones to support quantitative studies was
recognized at a NIST workshop in 2006.** NIST’s is the first phantom
designed to ensure that MRI system properties and image data are
traceable to international system of units (SI) standards. The ISMRM Ad
Hoc Committee on Standards for Quantitative MR defined the phantom
requirements and values. NIST modeled and built the prototype device and
assured the accuracy of measured quantities. NIST also developed and
tested various solutions used in the mini-spheres as contrast-enhancing
agents and measurement reference markers. Phannie will now undergo
testing at other institutions for about four months.
Stephen Russek, the physicist leading NIST’s
part of the project, says the phantom is intended to be not only
accurate and traceable but also physically stable and affordable, so
that it can become as widely used in MRI machines as seatbelts are in
cars. He demonstrated the durability of the mini-spheres by bouncing one
on the floor. Materials for Phannie cost $10,000, but hopefully, in
mass production the cost per phantom can be reduced to $2,000, he says.
“If it’s accurate, reliable and affordable,
then you have a way to measure the accuracy of MRI scanners all across
the country,” Russek says. “If used routinely, it will allow us to get a
complete snapshot of the quality and consistency of scanning.”
* Joint annual meeting of the International
Society for Magnetic Resonance in Medicine and the European Society for
Magnetic Resonance in Medicine and Biology, May 1-7, 2010, Stockholm,
** U.S. Measurement System Workshop on
Imaging as a Biomarker: Standards for Change Measurements in Therapy,
Sept. 14-15, 2006, Gaithersburg, Md.
Media Contact: Laura Ost, firstname.lastname@example.org, (303) 497-4880