Analysis for quantifying microscopic diffusion anisotropy

Abstract

The present invention describes a method for quantifying microscopic diffusion anisotropy and/or mean diffusivity in a material by analysis of echo attenuation curves acquired with two different gradient modulations schemes, wherein one gradient modulation scheme is based on isotropic diffusion weighting and the other gradient modulation scheme is based on non-isotropic diffusion weighting, and wherein the method comprises analyzing by comparing the signal decays of the two acquired echo attenuation curves.

1 . (canceled) 
     
     
         2 . Method for quantifying microscopic diffusion anisotropy and/or mean diffusivity in a material, said method comprising yielding an estimated value of microscopic fractional anisotropy (μFA) for quantifying anisotropy on the microscopic scale. 
     
     
         3 . Method according to  claim 2 , wherein the method is performed on any combination of 1D, 2D and/or 3D diffusion encoding. 
     
     
         4 . Method according to  claim 3 , wherein the microscopic fractional anisotropy (μFA) is obtained from signal attenuation from different diffusion encoding. 
     
     
         5 . Method according to  claim 3 , wherein the microscopic fractional anisotropy (μFA) is obtained as a function of radial and axial diffusivity. 
     
     
         6 . Method according to  claim 2 , wherein μFA is defined so that the μFA values correspond to the values of the well-established FA when diffusion is locally purely anisotropic and determined by randomly oriented axially symmetric diffusion tensors with identical eigenvalues. 
     
     
         7 . Method according to  claim 2 , wherein the microscopic fractional anisotropy (μFA) is calculated from mean diffusivity ( D ) and difference in second central moments of diffusion distribution (μ 2 ) from 1D, 2D or 3D diffusion encoding. 
     
     
         8 . A method according to  claim 2 , wherein the estimated value of microscopic fractional anisotropy (μFA) is used together with anyone of the parameters mean diffusivity ( D ), √{square root over (μ 2   iso )}/ D , fraction of the additional diffusion contribution (f) and/or diffusivity of the additional contribution (D 1 ), or any other parameter(s) calculated from μ 2 , μ 2   iso  or mean diffusivity, for generating parameter maps in MRI or for generating MR image contrast. 
     
     
         9 . A method according to  claim 2 , wherein the method also comprises analysis of echo attenuation curves acquired with two different gradient modulations schemes. 
     
     
         10 . Method according to  claim 9 , wherein the echo attenuation curves acquired with at least one of the gradient modulation scheme is based on non-isotropic diffusion weighting and is averaged across multiple encoding directions. 
     
     
         11 . Method according to  claim 9 , wherein comparing the signal decays of the acquired echo attenuation curves involves analysis of the ratio and/or difference between the acquired echo attenuation curves. 
     
     
         12 . Method according to  claim 2 , wherein the method is performed in an NMR and/or MRI method or experiment, or in combination with another NMR or MRI method. 
     
     
         13 . Method according to  claim 9 , wherein the acquired echo attenuation curves (logE vs. b, where E is echo amplitude and b is the diffusion weighting factor) are compared in terms of initial value, initial slope or curvature, and/or the ratio between the two echo attenuation curves is determined, so that the degree of microscopic anisotropy may be determined. 
     
     
         14 . Method according to  claim 2 , wherein a fit function comprising the parameters initial value, initial slope and curvature (zeroth, first, and second central moment of the probability distribution of diffusion coefficients), fraction of the additional diffusion contribution (f) and/or diffusivity of the additional contribution (D 1 ) are used. 
     
     
         15 . Method according to  claim 2 , wherein an echo attention curve acquired with the gradient modulation scheme is based on isotropic diffusion and is assumed to be monoexponential. 
     
     
         16 . Method according to  claim 2 , wherein the method involves approximating the distribution of apparent diffusion coefficients by using a Gamma distribution and the signal attenuation by its Laplace transform.