Multivariate combination of magnetization transfer, T2* and B0 orientation to study the myelo-architecture of the in vivo human cortex

Abstract Recently, T 2 * imaging at 7 Tesla (T) MRI was shown to reveal microstructural features of the cortical myeloarchitecture thanks to an increase in contrast-to-noise ratio. However, several confounds hamper the specificity of T 2 * measures (iron content, blood vessels, tissues orientation). Another metric, magnetization transfer ratio (MTR), is known to also be sensitive to myelin content and thus would be an excellent complementary measure because its underlying contrast mechanisms are different than that from T 2 *. The goal of this study was thus to combine MTR and T 2 * using multivariate statistics in order to gain insights into cortical myelin content. Seven healthy subjects were scanned at 7 T and 3 T to obtain T 2 * and MTR data, respectively. A multivariate myelin estimation model (MMEM) was developed, and consists in (i) normalizing T 2 * and MTR values and (ii) extracting their shared information using independent component analysis (ICA). B0 orientation dependence and cortical thickness were also computed and included in the model. Results showed high correlation between MTR and T 2 * in the whole cortex (r = 0.76, p  − 16 ), suggesting that both metrics are partly driven by a common source of contrast, here assumed to be the myelin. Average MTR and T 2 * were respectively 31.0 +/− 0.3% and 32.1 +/− 1.4 ms. Results of the MMEM spatial distribution showed similar trends to that from histological work stained for myelin (r = 0.77, p  This study demonstrates that MTR and T 2 * are highly correlated in the cortex. The combination of MTR, T 2 *, CT and B0 orientation may be a useful means to study cortical myeloarchitecture with more specificity than using any of the individual methods. The MMEM framework is extendable to other contrasts such as T 1 and diffusion MRI.