TY - JOUR
T1 - Mapping magnetic susceptibility anisotropies of white matter in vivo in the human brain at 7T
AU - Li, Xu
AU - Vikram, Deepti S.
AU - Lim, Issel Anne L.
AU - Jones, Craig K.
AU - Farrell, Jonathan A.D.
AU - van Zijl, Peter C.M.
N1 - Funding Information:
This project was supported by the National Center for Research Resources and the National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health through resource grant P41 EB015909 . The authors would like to thank Mr. Joseph Gillen, Ms. Terri Brawner, Ms. Kathleen Kahl, Ms. Ivana Kusevic, and Dr. Raj Stewart for their assistance with data acquisition and Dr. Andreia Faria for her assistance with the determination of susceptibility values using white matter region from the DTI brain atlas. Dr. Peter van Zijl is a paid lecturer for Philips Medical Systems and is the inventor of technology that is licensed to Philips. Dr. Craig Jones is paid in part through a grant to Kennedy Krieger Institute from Philips Medical Systems . This arrangement has been approved by The Johns Hopkins University in accordance with its Conflict of Interest policies.
PY - 2012/8/1
Y1 - 2012/8/1
N2 - High-resolution magnetic resonance phase- or frequency-shift images acquired at high field show contrast related to magnetic susceptibility differences between tissues. Such contrast varies with the orientation of the organ in the field, but the development of quantitative susceptibility mapping (QSM) has made it possible to reproducibly image the intrinsic tissue susceptibility contrast. However, recent studies indicate that magnetic susceptibility is anisotropic in brain white matter and, as such, needs to be described by a symmetric second-rank tensor (χ--). To fully determine the elements of this tensor, it would be necessary to acquire frequency data at six or more orientations. Assuming cylindrical symmetry of the susceptibility tensor in myelinated white matter fibers, we propose a simplified method to reconstruct the susceptibility tensor in terms of a mean magnetic susceptibility, MMS=(χ//+2χ⊥)/3 and a magnetic susceptibility anisotropy, MSA=χ //-χ ⊥, where χ // and χ ⊥ are susceptibility parallel and perpendicular to the white matter fiber direction, respectively. Computer simulations show that with a practical head rotation angle of around 20°-30°, four head orientations suffice to reproducibly reconstruct the tensor with good accuracy. We tested this approach on whole brain 1×1×1mm 3 frequency data acquired from five healthy subjects at 7T. The frequency information from phase images collected at four head orientations was combined with the fiber direction information extracted from diffusion tensor imaging (DTI) to map the white matter susceptibility tensor. The MMS and MSA were quantified for regions in several large white matter fiber structures, including the corona radiata, posterior thalamic radiation and corpus callosum. MMS ranged from -0.037 to -0.053ppm (referenced to CSF being about zero). MSA values could be quantified without the need for a reference and ranged between 0.004 and 0.029ppm, in line with the expectation that the susceptibility perpendicular to the fiber is more diamagnetic than the one parallel to it.
AB - High-resolution magnetic resonance phase- or frequency-shift images acquired at high field show contrast related to magnetic susceptibility differences between tissues. Such contrast varies with the orientation of the organ in the field, but the development of quantitative susceptibility mapping (QSM) has made it possible to reproducibly image the intrinsic tissue susceptibility contrast. However, recent studies indicate that magnetic susceptibility is anisotropic in brain white matter and, as such, needs to be described by a symmetric second-rank tensor (χ--). To fully determine the elements of this tensor, it would be necessary to acquire frequency data at six or more orientations. Assuming cylindrical symmetry of the susceptibility tensor in myelinated white matter fibers, we propose a simplified method to reconstruct the susceptibility tensor in terms of a mean magnetic susceptibility, MMS=(χ//+2χ⊥)/3 and a magnetic susceptibility anisotropy, MSA=χ //-χ ⊥, where χ // and χ ⊥ are susceptibility parallel and perpendicular to the white matter fiber direction, respectively. Computer simulations show that with a practical head rotation angle of around 20°-30°, four head orientations suffice to reproducibly reconstruct the tensor with good accuracy. We tested this approach on whole brain 1×1×1mm 3 frequency data acquired from five healthy subjects at 7T. The frequency information from phase images collected at four head orientations was combined with the fiber direction information extracted from diffusion tensor imaging (DTI) to map the white matter susceptibility tensor. The MMS and MSA were quantified for regions in several large white matter fiber structures, including the corona radiata, posterior thalamic radiation and corpus callosum. MMS ranged from -0.037 to -0.053ppm (referenced to CSF being about zero). MSA values could be quantified without the need for a reference and ranged between 0.004 and 0.029ppm, in line with the expectation that the susceptibility perpendicular to the fiber is more diamagnetic than the one parallel to it.
KW - Diffusion tensor imaging
KW - High field
KW - Magnetic susceptibility anisotropy
KW - Mean magnetic susceptibility
KW - Susceptibility tensor imaging
KW - White matter
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U2 - 10.1016/j.neuroimage.2012.04.042
DO - 10.1016/j.neuroimage.2012.04.042
M3 - Article
C2 - 22561358
AN - SCOPUS:84861598773
SN - 1053-8119
VL - 62
SP - 314
EP - 330
JO - NeuroImage
JF - NeuroImage
IS - 1
ER -