Optimization of endoluminal loop radiofrequency coils for gastrointestinal wall MR imaging

In this paper, we describe the optimization of endoluminal planar coils for high-resolution magnetic resonance imaging of gastrointestinal walls. For maximizing the coil performances, electromagnetic parameters of planar rectangular radio frequency (RF) coils were simulated using the finite element method. The eddy currents were fully computed to determine the electromagnetic losses in both wires and surrounding environment. Geometric parameters of the coils (length, conductive layer section, number of layers, and turns number) were varied. Based on simulations, five loop RF coil prototypes with planar geometry were designed to fit in a 5-mm inner diameter catheter. In the immediate vicinity of single-loop coils, the signal-to-noise ratio (SNR) decreases with the length of the coil, whereas penetration depth increases with it. The double-loop coil offers a greater penetration depth in comparison to the same length single-loop coil. The multilayer coil preserves the RF field B₁ by inducing a reduction in the electrical resistance of the conductor, therefore resulting in an increase in SNR. Experimental verifications were performed on a 1.5 T clinical scanner. Simulation results were found to be in good agreement with that of MR experiments. Developed prototypes provided a dramatic increase in SNR at the region of interest.