NEMA Test Standards Measure Performance Parameters for MRI Systems
August 9, 2006 // Published as a news service by IHS
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National Electrical Manufacturers Association (NEMA) published four standards that are part of a series of test standards developed by the medical diagnostic imaging industry for measuring performance parameters (e.g., noise levels, energy deposition and electric field strength) that govern image quality of magnetic resonance imaging (MRI) systems.
NEMA MS 4-2006 - Acoustic Noise Measurement Procedure for Diagnostic Magnetic Resonance Imaging Devices - was revised.
NEMA MS 10-2006 - Determination of Local Specific Absorption Rate (SAR) in Diagnostic Magnetic Resonance Imaging, NEMA MS 11-2006 - Determination of Gradient-Induced Electric Fields in Diagnostic Magnetic Resonance Imaging and NEMA MS 12-2006 - Quantification and Mapping of Geometric Distortion for Special Applications are new.
NEMA MS 4 has undergone a substantial revision because the gradient performance of modern MRI scanners has advanced significantly, making some basic assumptions and guidance in the original standard obsolete.
NEMA MS 10 is used for measuring local regions of high specific absorption rate (SAR) from radiofrequency (RF) power deposition. NEMA standard MS 8 is useful for measuring whole-body average SAR. By using both NEMA MS 8 and NEMA MS 10, it is possible to completely characterize RF power deposition both whole-body and local.
"Research has demonstrated that localized heating is a limiting safety factor in MRI and it is becoming increasingly important to characterize this local heating as MRI technology advances," said Michael Steckner of Hitachi Medical Systems and a member of the NEMA Magnetic Resonance Technical Committee. "This standard provides the tools to experimentally measure localized heating, complementing the MS 8 standard and thereby extending and enhancing our understanding of this important safety issue."
NEMA MS 11 presents a measurement method for determining gradient-induced electric fields, which affect the safety and comfort of patients. "As gradient system performance increases, there is also a need for experimental tools to quantify the gradient induced electric fields," said Steckner. "MS 11 provides the tools to experimentally measure these electric fields and complements the international MR safety standard, IEC 60601-2-33 (2002), which sets limits for patient safety and comfort."
According to NEMA, these test standards are intended for use by equipment manufacturers, testing houses, prospective purchasers and users alike. Manufacturers are permitted to use these standards to determine system performance specifications. The parameters supplied with each NEMA measurement serve as a guide to those factors that can influence the measurement. These standards can also serve as reference procedures for acceptance testing and periodic quality assurance.
According to NEMA, the demand for medical imaging is increasing both in volume and scope, requiring a detailed analysis of MRI scanner geometric distortion characteristics for some of the new special applications. NEMA MS 12 provides a series of recommendations on how to measure and present the distortion analysis information in order to meet this growing need.
Source: National Electrical Manufacturers Association (NEMA).