The modular (twin) gradient coil--high resolution, high contrast, diffusion weighted EPI at 1.0 Tesla

The modular (twin) gradient coil is a novel and effective approach to obtaining flexible and high power gradient performance without (i) peripheral nerve stimulation and (ii) the need for resonant or expensive high voltage gradient power supply units (PSU). This whole-body gradient system contains, on the same former, two independent sets of gradient coils, the conventional coil set and the short-body coil set. Each gradient axis is able to operate, independently, in any one of three modes. The third, combined, mode is realized by connecting the conventional coils and short-body coils in series. Through careful design of the shape and size of the linear volume of each mode of operation, the modular gradient coil is able to utilize the power, from a single gradient PSU, more efficiently and more appropriately, as determined by the application. In the short-body and combined modes the gradient fields are linear over a volume suitable for whole head/neck, liver and cardiovascular applications. In the conventional mode, a reduced performance is possible but over a much larger (conventional) imaging volume. Utilizing a semi-conductor switching arrangement it is possible to switch between modes in as little as 1 ms. By mixing different modes of operation on different gradient axes it is possible to utilize more efficiently, and safely, the properties of gradient performance best suited to the sequence requirements. Diffusion weighted EPI (DW-EPI) is a particular technique that demands the extremes of gradient system performance in terms of both amplitude and slew rate. DW-EPI has been implemented, using the modular gradient system, on a 1.0 Tesla whole-body MRI system. The preliminary results presented here serve to illustrate the advantages of the modular gradient coil in of itself as well as the direct benefits it provides for DW imaging at 1.0 Tesla.