Methods for Function ‘dwiMixtensor’ in Package ‘dti’
Description
The method estimates, in each voxel, a mixture of radial symmetric tensors from the DWI data contained in an object of class "dtiData"
.
Usage
1 2 3 4 5 6 7 8  ## S4 method for signature 'dtiData'
dwiMixtensor(object, maxcomp=3,
model=c("MT","MTiso","MTisoFA","MTisoEV"), fa=NULL,
lambda=NULL, reltol=1e10, maxit=5000, ngc=1000,
nguess=100*maxcomp^2, msc=c("BIC","AIC","AICC","none"),
mc.cores = setCores(,reprt=FALSE))
## S4 method for signature 'dwiMixtensor,dwiMixtensor'
dwiMtCombine(mtobj1, mtobj2, msc="BIC", where=NULL)

Arguments
object 
Object of class 
maxcomp 
Maximal number of mixture components. 
model 
Specifies the mixture model used. 
fa 
Value for FA in case of 
lambda 
Value for first eigenvalue in case of 
reltol 
Relative tolerance for R's optim() function. 
maxit 
Maximal number of iterations in R's optim() function. 
ngc 
provide information on number of voxel processed, elapsed time and estimated remaining time after 
nguess 
number of guesses in search for initial estimates 
msc 
Criterion used to select the order of the mixture model, either

mtobj1 
For method 
where 
Mask of voxel for which 
mtobj2 
For method 
mc.cores 
Number of cores to use. Defaults to number of threads specified for openMP, see documentation of package awsMethods. Our experience suggests to use 46 cores if available. 
Details
For model=="MT"
the function estimates, in each voxel, a mixture of radial symmetric (prolate) tensors from the DWI data contained in an object of class "dtiData"
. The number of mixture components is selected depending on the data, with a maximum number of components specified by maxcomp
. Optimization is performed usin R's internal BFGS code with mixture weights (volumes of compartments
corresponding to a tensor component) computed using the LawsonHannson NNLS code.
In case of model=="MTiso"
the model additionally contains an isotropic compartment. Optimization uses the internal LBFGSB code.
model=="MTisoFA"
and model=="MTisoEV"
fix FA and eigenvalues
of the prolate tensors, respectively, in the tensor mixture model with isotropic compartment.
The method "dwiMtCombine"
enables to combine results obtained for the same
dwi data set with different specifications, e.g. for maximum number of components
mcomp
and settings that influence initial estimates. The combined result
contains in each voxel the best result from both reconstructions with respect to
the specified model selection criterion msc
.
Value
An object of class "dwiMixtensor"
.
Author(s)
Karsten Tabelow tabelow@wiasberlin.de
J\"org Polzehl polzehl@wiasberlin.de
References
Jian et al. (2007), A novel tensor distribution model for the diffusionweighted MR signal, NeuroImage 37, 164–176.
See Also
dtiData
,
readDWIdata
,
medinria
,
dtiData
,
dwiMixtensor
Examples
1  ## Not run: demo(mixtens_art)
