Ultra-high-speed MR imaging with slowly varying gradients

At present, echo planar imaging is the fastest technique for acquiring complete MR image data (<25 msec). A drawback of this class of imaging is the necessity of using very rapidly switched gradients, restricting echo planar imaging to MR images having highly specialized hardware. The authors have developed a slow-gradient alternative to echo planar imaging that nevertheless permits complete acquisition times comparable to the echo planar technique. Their technique employs multiple (50-100) small-tip nonselective excitations applied during a single cycle of a rotating gradient. The FID resulting from each excitation is sampled immediately in the presence of the rotating gradient. After 50-100 such excitation/acquisition sequences during a 1800 rotation of the gradient, an image can be reconstructed using the projection reconstruction technique. Advantages of this new high-speed MR imaging technique are demonstrated with preliminary experimental results