Success Story

NIST’s Standard Phantom Designed for Calibrating MRI Machines

NIST standard phantom

Magnetic resonance imaging (MRI), a widely used medical tool that relies on magnetic fields and ra- dio waves to visualize the body’s inter- nal structures, especially soft tissues, may soon become even more useful.

The National Institute of Standards and Technology (NIST) has devel- oped the first “phantom” for calibrat- ing MRI machines that is traceable to standardized values. The proto- type, named Phannie, was developed in collaboration with the standards committee of the International Soci- ety for Magnetic Res-onance in Medicine(ISMRM).

Traceable MRI cal-ibrations are expected to enable accurate, quantitative measure-ments of tumors and other disease markers that can be re-produced across many different patients, scanners and clinics over time and potentially reduce medical costs.

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.

The new phantom is intended to generate more accurate and consis- tent images, validate disease mecha- nisms 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 ef- ficacy of novel drugs.

NIST’s is the first phantom de-signed to ensure that MRI system properties and image data are trace- able to international system of units (SI) standards.

The ISMRM Ad Hoc Committee on Standards for Quantitative Mag- netic Resonance (SQMR) defined the phantom requirements and values. NIST modeled and built the proto- type 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.

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. “If it’s accurate, reliable and affordable, then you have a way to measure the accuracy of MRI scanners all across the country,” Russek said. “If used routinely, it will allow us to get a complete snapshot of the quality and consistency of scanning.”

Phannie is undergoing testing at biomedical imaging sites across the country under the guidance of the ISMRM Ad Hoc Committee on SQMR. Materials for Phannie cost $10,000; however, it is hoped that in mass production it will reduce the cost per phantom to $2,000, Russek said.