The impact of B1+ correction on MP2RAGE cortical T1 and apparent cortical thickness at 7T. Issue 6 (18th February 2018)

• Record Type: Journal Article
• Authors: Haast, Roy A.M.; Ivanov, Dimo; Uludağ, Kâmil
• Is Part Of: Human brain mapping. Volume 39:Issue 6(2018)
• Page Start: 2412
• Page End: 2425
• Publication Date: 2018-02-18
• Subjects: 7T MRI -- cortical thickness -- MP2RAGE -- quantitative T1 -- transmit bias field; Brain mapping -- Periodicals; 611.81
• DOI: 10.1002/hbm.24011
• Languages: English
• ISSNs: 1065-9471

Abstract

Abstract: Determination of cortical thickness using MRI has often been criticized due to the presence of various error sources. Specifically, anatomical MRI relying on T1 contrast may be unreliable due to spatially variable image contrast between gray matter (GM), white matter (WM) and cerebrospinal fluid (CSF). Especially at ultra‐high field (≥ 7T) MRI, transmit and receive B1 ‐related image inhomogeneities can hamper correct classification of tissue types. In the current paper, we demonstrate that residual B 1 + (transmit) inhomogeneities in the T1 ‐weighted and quantitative T1 images using the MP2RAGE sequence at 7T lead to biases in cortical thickness measurements. As expected, post‐hoc correction for the spatially varying B 1 + profile reduced the apparent T1 values across the cortex in regions with low B 1 +, and slightly increased apparent T1 in regions with high B 1 + . As a result, improved contrast‐to‐noise ratio both at the GM‐CSF and GM‐WM boundaries can be observed leading to more accurate surface reconstructions and cortical thickness estimates. Overall, the changes in cortical thickness ranged between a 5% decrease to a 70% increase after B 1 + correction, reducing the variance of cortical thickness values across the brain dramatically and increasing the comparability with normative data. More specifically, the cortical thickness estimates increased in regions characterized by a strong decrease of apparent T1 after B 1 + correction in regions with low B 1 + due to improved detection of the pial surface. The current results suggest that cortical thickness can be more accurately determined using MP2RAGE data at 7T if B 1 + inhomogeneities are accounted for.