Ultimate intrinsic SNR in magnetic resonance imaging by optimizing the EM field generated by internal coils

Abstract

A method to find the ultimate intrinsic signal-to-noise ratio (ISNR) in a magnetic resonance imaging experiment is applied to a human body model. The method uses cylindrical wave expansion to represent an arbitrary electromagnetic field inside the body. This field is optimized to give the maximum possible ISNR for some point of interest from which the signal is received, and repeated for all points inside the body. Optimization is conducted by finding the set of coefficients associated with expansion modes that give the maximum ISNR. Application of this method enables the determination of the ultimate ISNR and the associated optimum electromagnetic field without the necessity of finding the receiving coil configuration needed to obtain the ultimate value of ISNR. Results of this work can be used to examine the efficiency of already available commercial coils and how far they can be improved. Moreover, the solution can be used to determine the performance difference between internal and external Magnetic Resonance Imaging (MRI) coils. Finally, knowledge of the optimum electromagnetic field inside the human body can be used to find the coil configuration that can radiate this field by solving an inverse problem.