Multiecho Imaging with Suboptimal Spoiler Gradients

Abstract

Although multiecho imaging may be used to measure transverse relaxation (T2),B1andB0inhomogeneity generally gives rise to unwanted coherence pathway signals which result in erroneousT2measurements. One approach to suppressing this unwanted signal is to center each rf refocusing pulse between spoiler gradients which dephase the unwanted signal; however, hardware limitations often dictate the use of suboptimal spoiler gradients, that is, gradients that cannot provide sufficient dephasing strength. Using simulations, this work demonstrates that by means of a small additional spoiler gradient prior to the first rf refocusing pulse it is possible to reduce substantially the contribution from unwanted coherence pathways in multiecho imaging studies that use suboptimal spoiler gradients. This reduction of unwanted signal results in measuredT2values within ≈1% of values obtained using spoiler gradients of optimal strength. These results were found for a wide range of biologically relevantT1andT2values, missettings of the rf refocusing pulse as large as 5%, and frequency offsets of up to 25 Hz. Multiecho image data agreed with the simulations. Using the additional spoiler gradient it is possible to reduce spoiler gradient strengths by up to 75%.