dtiTensor-methods {dti}R Documentation

Methods for Function ‘dtiTensor’ in Package ‘dti’

Description

The method estimates, in each voxel, the diffusion tensor from the DWI data contained in an object of class "dtiData".

Usage

  ## S4 method for signature 'dtiData':
  dtiTensor(object, method="nonlinear", varmethod="replicates", varmodel="local")

Arguments

object Object of class "dtiData"
method Method for tensor estimation. May be "linear", or "nonlinear".
varmethod Specifies the method for estimating the error variance. May be "replicates".
varmodel Specifies the model for the variance. May be "global", or "local".

Value

An object of class "dtiTensor".

Methods

obj = "ANY"
Returns a warning.
obj = "dtiData"
Estimate diffusion tensor from data in each voxel with the different options for the regression type and model for variance estimation. If method=="linear" estimates are obtained using a linearization of the tensor model. This was the estimate used in Tabelow et.al. (2008). method=="nonlinear" uses a nonlinear regression model with reparametrization that ensures the tensor to be positive semidefinite, see Koay et.al. (2006). If varmethod=="replicates" the error variance is estimated from replicated gradient directions if possible, otherwise an estimate is obtained from the residual sum of squares. If varmodel=="global" a homogeneous variance is assumed and estimated as the median of the local variance estimates.

Author(s)

Karsten Tabelow tabelow@wias-berlin.de
J"org Polzehl polzehl@wias-berlin.de

References

K. Tabelow, J. Polzehl, H.U. Voss, and V. Spokoiny. Diffusion Tensor Imaging: Structural adaptive smoothing, NeuroImage 39(4), 1763-1773 (2008).

C.G. Koay, J.D. Carew, A.L. Alexander, P.J. Basser and M.E. Meyerand. Investigation of Anomalous Estimates of Tensor-Derived Quantities in Diffusion Tensor Imaging, Magnetic Resonance in medicine, 2006, 55, 930-936.

http://www.wias-berlin.de/projects/matheon_a3/

See Also

dtiData, readDWIdata, dtiIndices-methods, medinria, dtiData, dtiTensor

Examples

  ## Not run: demo(dti_art)

[Package dti version 0.6-0 Index]