Background:The minimum admissible detuning efficiency of a receive coil is an essential parameter for coil designers. A receive coil with inefficient detuning leads to inhomogeneous B$_1$ during excitation. Previously proposed criteria for quantifying the detuning efficiency rely on indirect measurements and are difficult to implement.Purpose:To present an alternative method to quantify the detuning efficiency of receive-only surface coilsStudy type:Theoretical study supported by simulations and phantom experiments. Phantoms: Uniform spherical (100 mm diameter) and cylindrical (66 mm diameter) phantoms. Field strength/sequence: Dual repetition time B$_1$ mapping sequence at 1.5 T, and Bloch-Siegert shift B1 mapping sequence at 3.0 T. Assessment:One non-planar (80 mm × 43 mm$^2$) and 2 planar (40 mm and 57 mm diameter) surface coils were built. Theoretical analysis was performed to determine the minimum detuning efficiency required to avoid B$_1$ distortions. Experimental B$_1$ maps were acquired for the non-planar and planar surface coils at both 1.5 T and 3.0 T and visually compared with simulated B1 maps to assess the validity of the theoretical analysis.Statistical tests: None.Results: Based on the theoretical analysis, the proposed minimum admissible detuning efficiency, defined as DE$_{thr}$= 20 Log (Q) + 13 dB, depended only on the quality factor (Q) of the coil and was independent of coil area and field strength. Simulations and phantom experiments showed that when the detuning efficiency was higher than this minimum threshold level, the B$_1$ field generated by the transmission coil was not modified by the receive coil. Data conclusion: The proposed criterion for assessing the detuning efficiency is simple to measure, and does not depend on the area of the coil or on the magnetic field strength, up to 3T. Experimental and simulated B$_1$ maps confirmed that detuning efficiencies above the theoretically derived minimal admissible detuning efficiency resulted in a non-distorted B$_1$ field.< Réduire