TY - JOUR
T1 - Orientation-independent diffusion imaging without tensor diagonalization
T2 - Anisotropy definitions based on physical attributes of the diffusion ellipsoid
AU - Uluǧ, Aziz M.
AU - Van Zijl, Peter C.M.
PY - 1999/6
Y1 - 1999/6
N2 - Diffusion tensor imaging can provide a complete description of the diffusion process in tissue. However, this description is not unique but is orientation dependent, and, to quantify properly the intrinsic orientation- independent diffusion properties of the tissue, a set of three rotationally invariant quantities is needed. Instead of using the tensor eigenvalues for this, we define a new set consisting of scaled invariants that have the proper magnitude of actual diffusion constants and that are directly related to the physical attributes of the diffusion ellipsoid, namely, its average radius, surface, and volume. Using these three physical invariants, a new family of anisotropy measures is defined that are normalized between zero (isotropic) and one (completely anisotropic). Because rotational invariants are used, this approach does not require tensor diagonalization and eigenvalue determination and is therefore not susceptible to potential artifacts induced during these number manipulations. The relationship between the new anisotropy definitions and existing orientation-independent anisotropy indices obtained from eigenvalues is discussed, after which the new approach is evaluated for a group of healthy volunteers.
AB - Diffusion tensor imaging can provide a complete description of the diffusion process in tissue. However, this description is not unique but is orientation dependent, and, to quantify properly the intrinsic orientation- independent diffusion properties of the tissue, a set of three rotationally invariant quantities is needed. Instead of using the tensor eigenvalues for this, we define a new set consisting of scaled invariants that have the proper magnitude of actual diffusion constants and that are directly related to the physical attributes of the diffusion ellipsoid, namely, its average radius, surface, and volume. Using these three physical invariants, a new family of anisotropy measures is defined that are normalized between zero (isotropic) and one (completely anisotropic). Because rotational invariants are used, this approach does not require tensor diagonalization and eigenvalue determination and is therefore not susceptible to potential artifacts induced during these number manipulations. The relationship between the new anisotropy definitions and existing orientation-independent anisotropy indices obtained from eigenvalues is discussed, after which the new approach is evaluated for a group of healthy volunteers.
KW - Anisotropy
KW - Diffusion
KW - Human brain
KW - Imaging
KW - Tensor
KW - White matter
UR - http://www.scopus.com/inward/record.url?scp=0033035352&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0033035352&partnerID=8YFLogxK
U2 - 10.1002/(SICI)1522-2586(199906)9:6<804::AID-JMRI7>3.0.CO;2-B
DO - 10.1002/(SICI)1522-2586(199906)9:6<804::AID-JMRI7>3.0.CO;2-B
M3 - Article
C2 - 10373028
AN - SCOPUS:0033035352
SN - 1053-1807
VL - 9
SP - 804
EP - 813
JO - Journal of Magnetic Resonance Imaging
JF - Journal of Magnetic Resonance Imaging
IS - 6
ER -