Identifying intracortical partial voluming effects using cortical surface normals in quantitative MRI T1 maps sensitive to microstructure

Abstract

Partial voluming is a known problem in medical imaging. It occurs at high contrast edges between different structures. Image segmentation tasks can account for this type of effect to a certain degree, but residual intensity effects in structures located further away from affected edges remain. This paper focuses on partial volume (PV) effects at the interface between gray matter and cerebrospinal fluid in the brain when imaged using high-field magnetic resonance imaging (MRI). Here, we use cortical surface normals for spatially locating PV-induced effects on MRI measures of cortical microstructure. We demonstrate that especially in very narrow sulcal banks of the cortex, PV effects significantly influence cortical MRI intensities, but only up to a certain cortical depth. The method allows to investigate and better understand PV effects in the cortex to identify locations in which the MRI intensities can be fully trusted. The results may prove to be useful for future PV correction methods in brain segmentation. Also, cortical area studies may benefit from better PV estimation in order to yield more precise and confiding results on microstructure and areal extent.