Medical imaging is one of the device industry’s hottest fields, and it has seen a number of advances over the last several years. More advances are in store. The National Electrical Manufacturers Association (NEMA) has published two new standards to help improve image quality of magnetic resonance imaging systems. The first, MS 1-2008, Determination of Signal-to-Noise Ratio (SNR) in Diagnostic Magnetic Resonance Imaging, addresses the measurement of performance parameters governing image quality of MRI systems. The second, MS 3-2008, Determination of Image Uniformity in Diagnostic Magnetic Resonance Images, prescribes a method for measuring the nonuniformity of magnetic resonance images in order to characterize the low spatial frequency nonuniformities typical of such images.

According to NEMA, these MRI standards have been restructured to consider the coil geometry. In addition, new measurement methods have been added to this standard. The parameters serve as a guide to those factors that can influence the measurement. These standards also serve as reference procedures for acceptance testing and periodic quality assurance.

First developed in 1988 to define a standard procedure for measuring a useful index of image quality performance for MRIs, MS 1 describes four methods to measure image SNR. The standard is intended for use by both MRI manufacturers and manufacturers of accessory equipment (including radio-frequency coils).

The series of test standards was developed by the medical diagnostic imaging industry by the Magnetic Resonance Section of the Medical Imaging and Technology Alliance (MITA), a division of NEMA.

“It is important to quantify image nonuniformity because of the effect it has on image quality,” said Michael Steckner of MITA. “This standard characterizes image nonuniformity qualitatively with a gray-scale uniformity map and quantitatively with simple figures of merit that analyze the range of pixel intensities relative to some measure of the average image intensity,” he said.

The newly revised standard enables the use of both the American College of Radiology Magnetic Resonance Accreditation Program (ACR-MRAP) and IEC performance standard methods for determining image uniformity. Both methods are useful against variations in measurement SNR.

According to NEMA, to make the MS 3 standard consistent with the structure of related standards, it covers single-channel volume coils exclusively. For added flexibility, NEMA says that this edition has been modified to allow the gray-scale map definition of NEMA MS 6, Determination of Signal-to-Noise Ratio and Image Uniformity for Single-channel Non-Volume Coils in Diagnostic MR Imaging.

Sherrie Conroy
sherrie.conroy@cancom.com

An electronic copy of NEMA MS 1-2008 may be downloaded at no charge, or a hard copy may be purchased for $45, by visiting NEMA’s Web site at www.nema.org/stds/ms1.cfm. An electronic copy of NEMA MS 3-2008 may be downloaded at no charge, or a hard copy may be purchased for $48, by visiting NEMA’s Web site at www.nema.org/stds/ms3.cfm. Both standards can also be obtained by contacting IHS at 800-854-7179 (within the U.S.), 303-397-7956 (international), 303-397-2740 (fax), or on the Web at www.global.ihs.com. 

The prognosis for the medical device market is healthy. But the expanding market attracts more and more competitors. The competition for business growth and better return on investment places unrelenting pressure on today's medical equipment OEMs.