Though the electromagnetic technology has been contributing to the evolution of MRI, there are remaining problems to be worked out. With some introduction, this paper explains such problems focusing on the gradient coil design, RF coil design and RF safety consideration. For accurate, high-speed control of the gradient field, a new technology, shielded gradient coil has started playing an important role. The efficient design of such a coil requires a robust and efficient optimization tool that still has room for improvement. We propose to use the stored energy as the most important optimization parameter that may make the optimization process more efficient. Phased array RF coil, that widens the field of view while maintaining high SNR of a small RF coil, is a recent technology. For this, the system needs to have high capacity to acquire and process the data. To mitigate this problem, we are working on the combination of rather conventional QD technology with phased array. RF shielding between gradient coil and RF coil is becoming a serious problem with the evolution of high speed imaging techniques, and a complete solution is not yet demonstrated. We also discuss the difficulty of rigorous control of RF heating in patients. Practical method to predict local SAR needs to be developed.

A slotted tube resonator (STR) having a shield of conducting circular cylinder which is used as a probe for the magnetic resonance imaging (MRI) is analyzed by using the variational method and the dyadic Green's function of a circular waveguide. Three surface current modes are employed to expand the currents on the STR. Quadruple integrals appearing in the variational expression are evaluated analytically for saving the CPU time. Resonant frequency, Q value and the magnitude of magnetic field distributions for various radii of the shields are obtained to show the effects of the shield. Some measured date are compared with the theoretical results to confirm the validity of the present analysis.