RARE SPIRAL T-2-WEIGHTED IMAGING

Spiral imaging has a number of advantages for fast imaging, including an efficient use of gradient hardware. However, inhomogeneity-induced blurring is proportional to the data acquisition duration. In this pap er, we combine spiral data acquisition with a RARE echo train. This al lows a long data acquisition interval per excitation, while limiting t he effects of inhomogeneity. Long spiral k-space trajectories are part itioned into smaller, annular ring trajectories. Each of these annular rings is acquired during echoes of a RARE echo train. The RARE refocu sing RF pulses periodically refocus off-resonant spins while building a long data acquisition. We describe both T-2-weighted single excitati on and interleaved RARE spiral sequences. A typical sequence acquires a complete data set in three excitations (32 cm FOV, 192 x 192 matrix) . At a TR = 2000 ms, we can average two acquisitions in an easy breath -hold interval. A multifrequency reconstruction algorithm minimizes th e effects of any off-resonant spins. Though this algorithm needs a fie ld map, we demonstrate how signal averaging can provide the necessary phase data while increasing SNR. The field map creation causes no scan time penalty and essentially no loss in SNR efficiency. Multiple slic e, 14-s breath-hold scans acquired on a conventional gradient system d emonstrate the performance.