Smooth DWI data
Description
Adaptive smoothing of DWI data. Smoothing is performed both in space and on the sphere (e.g. between images obtained for different gradient directions) employing a natural
geometrical distance ( in SE(3)). Structural adaptation is used in space only.
Method dwi.smooth
refers to the original POAS approach for single shell data.
Method dwi.smooth.ms
implements an improved method that is applicable for both single and multishell data.
Usage
1 2 3 4 5 6 7 8 9 10  ## S4 method for signature 'dtiData'
dwi.smooth(object, kstar, lambda=20, kappa0=NULL, ncoils=1,
sigma=NULL, level=NULL, vred=4, xind=NULL,
yind=NULL, zind=NULL, verbose=FALSE, dist=1,
model=c("Gapprox","Gapprox2","Chi","Chi2"))
## S4 method for signature 'dtiData'
dwi.smooth.ms(object, kstar, lambda=12, kappa0=.5, ncoils=1,
sigma=NULL, ws0=1, level=NULL, mask = NULL, xind=NULL,
yind=NULL, zind=NULL, verbose=FALSE,
usemaxni=TRUE, memrelease = TRUE)

Arguments
object 
Object of class 
kstar 
Number of steps in structural adaptation 
lambda 
Scale parameter in adaptation 
kappa0 
determines amount of smoothing on the sphere. Larger values correspond to stronger smoothing on the sphere. If 
ncoils 
Number of coils in MR system 
sigma 
Error standard deviation. Assumed to be known and homogeneous in the current implementation. A reasonable estimate may be defined
as the modal value of standard deviations obtained using method 
level 
Threshold for image intensities when setting mask. 
mask 
Binary 3D image defining a mask 
vred 
Used if 
xind 
index for xcoordinate 
yind 
index for ycoordinate 
zind 
index for zcoordinate 
verbose 
If 
dist 
Distance in SE3. Reasonable values are 1 (default, see Becker et.al. 2012), 2 ( a slight modification of 1: with k6^2 instead of abs(k6)) and 3 (using a 'naive' distance on the sphere) 
model 
Determines which quantities are smoothed. Possible values are

ws0 
Factor to downweight information from S0 images, defaults
to 
usemaxni 
If 
memrelease 
If 
Value
An object of class "dtiData"
with smoothed diffusion weighted images.
Methods
signature(object) = "ANY"

Returns a warning.
signature(object) = "dtiData"

Smoothing of DWI data
Author(s)
Karsten Tabelow tabelow@wiasberlin.de
J\"org Polzehl polzehl@wiasberlin.de
See Also
dtiData
,
dtiData
,