Validation of numerical approaches for electromagnetic characterization of magnetic resonance radiofrequency coils

Numerical methods based on solutions of Maxwell's equations are usually adopted for the electromagnetic characterization of Magnetic Resonance (MR) Radiofrequency (RF) coils. In this context, many different numerical methods can be employed, including time domain methods, e.g., the Finite-Difference Time-Domain (FDTD), and frequency domain methods, e.g., the Finite Element Methods (FEM) and the Method of Moments (MoM). We provide a quantitative comparison of performances and a detailed evaluation of advantages and limitations of the aforementioned methods in the context of RF coil design for MR applications. Specifically, we analyzed three RF coils which are representative of current geometries for clinical applications: a 1.5 T proton surface coil; a 7T dual tuned surface coil; a 7T proton volume coil. The numerical simulation results have been compared with measurements, with excellent agreement in almost every case. However, the three methods differ in terms of required computing resources (memory and simulation time) as well as their ability to handle a realistic phantom model. For this reason, this work could provide "a guide to select the most suitable method for each specific research and clinical applications at low and high field"

Versatile coil design and positioning of transverse-field RF surface coils for clinical 1.5-T MRI applications.

Clinical MRI/MRS applications require radio frequency (RF) surface coils positioned at an arbitrary angle \u3b1 with respect to B0. In these experimental conditions the standard circular loop (CL) coil, producing an axial RF field, shows a large signal loss in the central region of interest (ROI). We demonstrate that transverse-field figure-of-eight (FO8) RF surface coils design are not subject to the same amount of signal loss in the central ROI as loop coils when their orientations are changed. The 1.5-T CL and FO8 prototypes (diameter = 10 cm) were built on Plexiglas using copper strips (width = 4 mm, thickness = 100 \u3bcm). The two linear elements of the FO8 coil were 1 cm apart. Axial spoiled gradient echo (SPGR) images of a phantom containing doped water were acquired with the coil plane at \u3b1=0\ub0, 45\ub0, and 90\ub0. As \u3b1 increases, the CL images show, in the central ROI, a signal that decreases from a maximum value to zero. Whereas the FO8 images show, in the same ROI, a signal that varies little from the maximum value (20%). Optimized FO8 coils can be oriented with the coil plane positioned along any direction with respect to B0 without significant signal loss. Transverse RF coil design should be useful for clinical MRS studies and also for parallel imaging techniques where versatile RF coils disposed along arbitrary directions are required

A novel Transverse Field RF Surface Coil for Clinical 1.5 T MRI and MRS Applications.

none8noneM. Alfonsetti; V. Clementi; S. Iotti; G. Placidi; R. Lodi; B. Barbiroli; A. Sotgiu; M. AlecciM. Alfonsetti; V. Clementi; S. Iotti; G. Placidi; R. Lodi; B. Barbiroli; A. Sotgiu; M. Alecc