DIR imaging using GRAPPA for Cortical thickness estimation

Introduction Most gray matter volumetric studies use T1-weighted imaging such as MP-RAGE because it provides good contrast between white matter and cortex. However, due to susceptibility artifact coming from the air-tissue interface (Fig. 1), a reliable and accurate measurement is difficult in the regions near the air-bone interface for T1-wieghted schemes. One way to alleviate this problem is to perform gray matter spin-echo imaging through double inversion recovery (DIR) sequence. The sequence selectively suppresses the signal from cerebrospinal fluid (CSF) and white matter using two inversion recovery pulses [1]. One drawback of the DIR sequence, however, is its long scan time. For high resolution 3D DIR imaging, orders on the order ±20 minutes can be required for full k-space coverage. This can be effectively reduced by using from a variety of parallel imaging schemes. The objective of this study was to determine the influence of undersampling with parallel imaging on cortical thickness measurements using a DIR acquisition scheme. Here, we applied one of the parallel imaging reconstruction schemes, namely, the Generalized Autocalibrating Partially Parallel Acquisition (GRAPPA) [2] scheme to DIR imaging to evaluate measurement changes as a function of reduction factor.