The National Electrical Manufacturers Association (NEMA) has published three standards for magnetic resonance imaging (MRI) systems.

MS 6-2008 Determination of Signal-to-Noise Ratio and Image Uniformity for Single-Channel Non-Volume Coils in Diagnostic MRI lists a method for evaluating single-channel non-volume special purpose radio-frequency coils used with MRIs. Excluded are system head and body coils, single-channel volume specialty coils, and coils that require multiple receiver channels for operation.
MS 8-2008 Characterization of the Specific Absorption Rate for MRI Systems defines calorimetric and pulse-energy methods for determining SARs in either a phantom or a patient. Results from either method may then be extrapolated to other scan parameters and even to other waveforms.

MS 9-2008 Characterization of Phased Array Coils for Diagnostic MRIs describes a standard way for measuring and reporting SNR and uniformity of signal intensity in images acquired with phased array coils. According to NEMA, these quantities are useful in evaluating the impact of system changes on performance or in demonstrating effectiveness for Federal Drug Administration applications.