title: The influence of molecular order and microstructure on the R2* and the magnetic susceptibility tensor.
abstract: In this work, we demonstrate that in the presence of ordered sub-voxel structure such as tubular organization, biomaterials with molecular isotropy exhibits only apparent R2* anisotropy, while biomaterials with molecular anisotropy exhibit both apparent R2* and susceptibility anisotropy by means of susceptibility tensor imaging (STI). To this end, R2* and STI from gradient echo magnitude and phase data were examined in phantoms made from carbon fiber and Gadolinium (Gd) solutions with and without intrinsic molecular order and sub-voxel structure as well as in the in vivo brain. Confidence in the tensor reconstructions was evaluated with a wild bootstrap analysis. Carbon fiber showed both apparent anisotropy in R2* and anisotropy in STI, while the Gd filled capillary tubes only showed apparent anisotropy on R2*. Similarly, white matter showed anisotropic R2* and magnetic susceptibility with higher confidence, while the cerebral veins displayed only strong apparent R2* tensor anisotropy. Ordered sub-voxel tissue microstructure leads to apparent R2* anisotropy, which can be found in both white matter tracts and cerebral veins. However, additional molecular anisotropy is required for magnetic susceptibility anisotropy, which can be found in white matter tracts but not in cerebral veins.
authors.affiliation: Department of Biomedical Engineering, Cornell University, Ithaca, NY, USA.
authors.forename: Cynthia
authors.initials: C
authors.lastname: Wisnieff
authors.affiliation: Department of Radiology, Weill Cornell Medical College, New York, NY, USA; Medimagemetric, LLC, New York, NY, USA.
authors.forename: Tian
authors.initials: T
authors.lastname: Liu
authors.affiliation: Department of Biomedical Engineering, Cornell University, Ithaca, NY, USA; Department of Radiology, Weill Cornell Medical College, New York, NY, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Radiology, Weill Cornell Medical College, New York, NY, USA. Electronic address: pas2018@med.cornell.edu.
authors.forename: Pascal
authors.initials: P
authors.lastname: Spincemaille
mesh_terms: D016880:Anisotropy; D001931:Brain Mapping / Q000379:methods; D002550:Cerebral Veins / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D056324:Diffusion Tensor Imaging / Q000379:methods*; D006801:Humans; D019047:Phantoms, Imaging; D012680:Sensitivity and Specificity; D066127:White Matter / Q000033:anatomy & histology / Q000000981:diagnostic imaging*
keywords: Anisotropy; Diffusion tensor imaging; R2* relaxation; Susceptibility tensor imaging; White matter; Wild bootstrap analysis