INCREASED FLEXIBILITY IN GRASE IMAGING BY K-SPACE-BANDED PHASE-ENCODING

GRASE (GRadient and Spin Echo) is an echo train imaging technique that combines gradient and RF refocusing. Although overall signal decay is with T-2 and field inhomogeneity phase errors do not accumulate, the small residual phase errors are periodic with echo number. The echo order described previously eliminates the phase error periodicity in k space but instead creates periodicity in the T-2 modulation function that can also cause artifacts. In addition, with this order, the effective TE must be half the echo train time, and asymmetric Fourier sampling is difficult to implement. A new method is described that greatly reduces artifacts due to T-2 decay, permits greater control of T-2 contrast, and lends itself to asymmetric Fourier sampling, Different time segments of the echo train are encoded with different bands of spatial frequency in k space (hence ''k banding''). Both computer simulations and experimental results demonstrate improvements in GRASE images acquired by this method.