Diffusion Feature Post-Menstrual Age Groups
28-31 Weeks 32-36 Weeks 37-40 Weeks 41-45 Weeks
Full Tensor
what is this?
Full Tensor
The full diffusion tensor is a 3x3 matrix with six unique elements. The
diffusion tensor can also be thought of as the co-variance matrix of a
normal distribution that captures the probability of water molecule
displacements. The tensor images provided here are given in log-Euclidean
space to ensure that any tensor arithmetic is performed correctly. For
more information on log-Euclidean space and tensors, please see the
original paper on the topic.
Fractional Anisotropy
what is this?
Fractional Anisotropy
Fractional Anisotropy (FA) is a measure of the variance in diffusion rates as
the direction of the diffusion changes. High FA values are typically associated
with fibrous tissue like the white matter of the brain, while the FA at a
voxel is zero when diffusion at that voxel is equal in all directions. For
more information on how FA is computed, please see
this paper .
Mean Diffusivity
what is this?
Mean Diffusivity
Mean Diffusivity (MD) is a measure of how much diffusion is occurring at a
given voxel. Larger MD implies less cell structure while smaller MD implies
the presence of significant cell structure. For more information on how MD
is computed, please see
this paper .
Primary Eigenvalue
what is this?
Primary Eigenvalue
The primary eigenvalue (L1) is the largest eigenvalue of the diffusion
tensor and is also referred to as axial diffusivity. In fibrous tissue, L1
indicates the rate of diffusion along the fibers at a voxel.
Secondary Eigenvalue
what is this?
Secondary Eigenvalue
The secondary eigenvalue (L2) is the second-largest eigenvalue of the
diffusion tensor. In fibrous tissue, L2 indicates the rate of diffusion
perpendicular to the fibers at a voxel.
Tertiary Eigenvalue
what is this?
Tertiary Eigenvalue
The Tertiary eigenvalue (L3) is the second-largest eigenvalue of the
diffusion tensor. In fibrous tissue, L3 indicates the rate of diffusion
perpendicular to the fibers at a voxel.
Radial Diffusivity
what is this?
Radial Diffusivity
Radial Diffusivity (RD) is the measure of the diffusion rate perpendicular
to the axonal fiber direction. RD is computed as the average of the two
smallest eigenvalues of the diffusion tensor. An abnormally high value of
RD may indicate axonal dematuration.
Linear Diffusion Coefficient
what is this?
Linear Diffusion Coefficient
The linear diffusion coefficient (CL) captures what fraction of the diffusion
at a voxel is confined to a single direction (or line). Large CL values would
be found in fibrous tissue where all the axons are aligned in the same
direction. For more information on how the linear diffusion coefficient is
computed, please see
this paper .
Planar Diffusion Coefficient
what is this?
Planar Diffusion Coefficient
The planar diffusion coefficient (CP) captures what fraction of the diffusion
at a voxel is confined to a single plane. Large CP values would be found in
fibrous tissue where there are two axon populations that are crossing. For more
information on how the planar diffusion coefficient is computed,
please see
this paper .
Spherical Diffusion Coefficient
what is this?
Spherical Diffusion Coefficient
The spherical diffusion coefficient (CS) captures how isotropic, or spherical,
the diffusion profile is. Larges CS values indicate that the axons at a
particular voxel are not coherently aligned in a single direction. For more
information on how the spherical diffusion coefficient is computed,
please see
this paper .
Relative Anisotropy
what is this?
Relative Anisotropy
Relative anisotropy (RA) is a measure of the variance in diffusion rates as
the direction of the diffusion changes. It is computed in a similar fashion
to fractional anisotropy and is known to have a lower signal-to-noise ratio.
Like fractional anisotropy, large RA values occur in fibrous tissue while
smaller RA values occur in areas where there is no preferred direction of
diffusion. For more information on how relative anisotropy is computed,
please see
this paper .
log-Fractional Anisotropy
what is this?
log-Fractional Anisotropy
log-Fractional Anisotropy (LFA) is the fractional anisotropy computed from
the log-Euclidean diffusion tensor. LFA behaves in a similar way to fractional
anisotropy: large LFA values occur in fibrous tissue while smaller LFA values
occur in areas where there is no preferred direction of diffusion. For more
information on log-Euclidean tensors, please see the
original paper
on the topic. For more information on how fractional anisotropy is computed,
please see
this paper .
Tensor Norm
what is this?
Tensor Norm
The tensor norm (VOL) is exactly what it sounds like: the Frobenious norm of
the diffusion tensor. Like mean diffusivity, VOL tells us how much diffusion
is occurring at a given voxel. Larger VOL implies less cell structure while
smaller VOL implies the presence of significant cell structure.
Volume Ratio
what is this?
Volume Ratio
Volume ratio (VR) is a measure of how spherical, or isotropic, the diffusion
profile is at a given voxel. A high measure of VR suggests that the volume of
the diffusion tensor ellipsoid is very close to the volume of a sphere with a
diameter equal to the average length of the ellipsoid axes. More information
on the volume ratio can be found in
this paper
