ftm {dcemri} | R Documentation |
Motion correction and/or co-registration of three-dimensional arrays (medical imaging data) are performed by applying a user-defined mask of voxels. Normalized cross-correlations (in 3D) are computed using the FFT.
ftm(input, mask, template, plot=FALSE, ...)
input |
is a four-dimensional array of signal intensities. |
mask |
is a three-dimensional array of logical values (voxels
to be included are TRUE , and voxels to be excluded are
FALSE ). |
template |
is a three dimensional array (the same structure as
mask ) that contains the signal intensities associated with
the reference data. |
plot |
is a flag that determines if a plot of the motion
correction as a function of the fourth dimension (default =
FALSE ). |
... |
Additional variables passed to the plot function. |
An extremely basic method of motion correction/co-registration is
implemented by estimating “local” cross-correlations based on a
binary mask that is a subset of the original three-dimensional volume.
All convolutions are preformed via the FFT (fft
) and
repetitive calculations are minimized where possible.
Only whole-voxel translations are considered. This does not begin to capture the true effects of motion in soft tissue, but we assume that the object of interest (e.g., tumor) is a fairly rigid structure. Potential extensions include rigid-body, affine and nonlinear registration techniques along with interploation schemes in order to capture intra-voxel manipulations of the data.
A list of objects are returned:
out |
Motion-corrected version of the four-dimensional array. |
offset |
Translations (in 3D) for each volume in the 4D array. |
t.center |
Estimated center of the binary mask. |
Brandon Whitcher
Lewis, J.P. (2003) Fast normalized cross-correlation. www.idiom.com/~zilla/
conv.fft
, find.center
, shift3D