Increased gradient magnetic field efficiency and faster switching speed are crucial to achieving the improved spatial and velocity resolution for Magnetic Resonance Imaging (MRI) in reduced imaging time. Modern MRI systems are moving in the ultra-short direction for patient comfort (less claustrophobic), easy access, weight, etc. But how far can we push the technological limit for gradient coil design? We desire high-strength, low-inductance, short gradient coils of large imaging regions. However, there are trade-offs between these requirements. So given certain conditions, what is the best performance coil we can design? This question is of great interest to the MRI community, yet not sufficiently answered to date.

Moreover, when faster switching higher-strength gradients are being produced, physiological effects come into play. Specifically, peripheral nerve stimulation -- tingling or tapping sensations caused by a time varying magnetic field -- affect patient comfort and safety. It is thus important to characterize the operable region for existing gradient coils in terms of nerve stimulation. Moreover, we need to be able to predict the stimulation property of a certain coil design before building it. Hence the overall goal of this project is to design gradient coils of the best technological performance within the physiological constraints set

To date, we have developed a design strategy for ultra-short MRI gradient coils. We have conducted a design study to assess the performance trade-offs for ultra-short, symmetric gradient coils, where the parameters of interest are gradient efficiency, coil inductance and region of uniformity (ROU) size/position relative to coil dimensions. We have derived a universal law for the design of optimum length short coils. We are aiming at designing a small body size coil to be used in a high field MRI system. This coil will be designed to image mainly head and neck, possibly whole body in future. The final design will be chosen from a series of preliminary results according to the universal law before we proceed to the actual building stage. Figure 1 (shown below) is an example of the candidate coil patterns.

However, it is known that the time-varying magnetic field can induce electric fields in the human body, and if this electric field is of sufficient magnitude will induce nerve stimulation. This phenomenon is called "magnetostimulation". With stronger and stronger gradient coils designed and built nowadays, the issue of magnetostimulation becomes more and more important. In order to understand and predict peripheral nerve stimulation effects of gradient coils in depth, both experimental study on human volunteers and theoretical modeling are being carried out. By studying the theory, performing simulations based on the coil design information, and comparing them against the experimental results, the existing stimulation models will be tested and improved. This part of the research will lead to the prediction of whether a certain high-strength coil design is actually beneficial to clinical applications before it starts to stimulate patients.