DTI Data in Camino

John Muschelli

Resources and Goals

Much of this work has been adapted by the FSL guide for DTI reconstruction: http://camino.cs.ucl.ac.uk/index.php?n=Tutorials.DTI. We will show you a few steps that have been implemented in rcamino: camino_pointset2scheme, camino_modelfit, camino_fa, camino_md, and camino_dteig.

Data Location

The data located in this tutorial is located at http://cmic.cs.ucl.ac.uk/camino//uploads/Tutorials/example_dwi.zip. It contains 3 files:

  1. 4Ddwi_b1000.nii.gz - a 4D image of the DWI data.
  2. brain_mask.nii.gz - A brain mask of the DTI data
  3. grad_dirs.txt - a 3 column text file with the b-vectors as the first 3 columns

Reading in the Data

First, we download the data into a temporary directory the unzip it:

tdir = tempdir()
tfile = file.path(tdir, "example_dwi.zip")
download.file("http://cmic.cs.ucl.ac.uk/camino//uploads/Tutorials/example_dwi.zip",
              destfile = tfile)
files = unzip(zipfile = tfile, exdir = tdir, overwrite = TRUE)

Making b-vectors and b-values

As dtifit requires the b-values and b-vectors to be separated, and this data has b-values of \(1000\) when the b-vectors is not zero. This is very important and you must know where your b-values and b-vectors are when doing your analyses and what units they are in.

Registered S3 method overwritten by 'R.oo':
  method        from       
  throw.default R.methodsS3
/tmp/RtmpsRfqHp/Rinst7ed24cd45286/rcamino/camino/bin/pointset2scheme -inputfile '/tmp/RtmpMOnBkd/grad_dirs.txt' -bvalue 1000000000 -outputfile /tmp/RtmpMOnBkd/file23752fb1763.scheme

Checking our data

Here we ensure that the number of b-values/b-vectors is the same as the number of time points in the 4D image.

Loading required package: oro.nifti
oro.nifti 0.10.1
[1] 33
[1] 33
          used (Mb) gc trigger  (Mb)  max used  (Mb)
Ncells  715368 38.3    1237794  66.2   1237794  66.2
Vcells 1282619  9.8  118756965 906.1 123736488 944.1

Running Image Conversion

We will save the result in a temporary file (outfile), but also return the result as a nifti object ret, as retimg = TRUE. We will use the first volume as the reference as is the default in FSL. Note FSL is zero-indexed so the first volume is the zero-ith index:

float_fname = camino_image2voxel(infile = img_fname, 
                                outputdatatype = "float")
/tmp/RtmpsRfqHp/Rinst7ed24cd45286/rcamino/camino/bin/image2voxel -inputfile '/tmp/RtmpMOnBkd/4Ddwi_b1000.nii.gz' -outputfile '/tmp/RtmpMOnBkd/file2375d30b6f2.Bfloat' -outputdatatype float

Note, from here on forward we will use either the filename for the output of the eddy current correction or the eddy-current-corrected nifti object.

Fit the diffusion tensor

mask_fname = grep("mask", files, value = TRUE)
model_fname = camino_modelfit(
  infile = float_fname,
  scheme = scheme_file,
  mask = mask_fname,
  outputdatatype = "double"
  )
/tmp/RtmpsRfqHp/Rinst7ed24cd45286/rcamino/camino/bin/modelfit -inputfile '/tmp/RtmpMOnBkd/file2375d30b6f2.Bfloat' -outputfile '/tmp/RtmpMOnBkd/file2377721d939.Bdouble' -inputdatatype float -schemefile /tmp/RtmpMOnBkd/file23752fb1763.scheme -bgmask /tmp/RtmpMOnBkd/brain_mask.nii.gz -maskdatatype float -model dt

Getting FA vlaues

cat '/tmp/RtmpMOnBkd/file2377721d939.Bdouble' |  /tmp/RtmpsRfqHp/Rinst7ed24cd45286/rcamino/camino/bin/fa -inputmodel dt -outputdatatype double > '/tmp/RtmpMOnBkd/file2372b7426b6.Bdouble'

Converting FA values back into an image

/tmp/RtmpsRfqHp/Rinst7ed24cd45286/rcamino/camino/bin/voxel2image -inputfile /tmp/RtmpMOnBkd/file2372b7426b6.Bdouble -header /tmp/RtmpMOnBkd/4Ddwi_b1000.nii.gz -outputroot /tmp/RtmpMOnBkd/file23730d7562d_ -components 1 -gzip

Converting with piping

We can chain Camino commands using the magrittr pipe operation (%>%):

cat '/tmp/RtmpMOnBkd/file2377721d939.Bdouble' |  /tmp/RtmpsRfqHp/Rinst7ed24cd45286/rcamino/camino/bin/fa -inputmodel dt -outputdatatype double > '/tmp/RtmpMOnBkd/file23774110eea.Bdouble'
/tmp/RtmpsRfqHp/Rinst7ed24cd45286/rcamino/camino/bin/voxel2image -inputfile /tmp/RtmpMOnBkd/file23774110eea.Bdouble -header /tmp/RtmpMOnBkd/4Ddwi_b1000.nii.gz -outputroot /tmp/RtmpMOnBkd/file2373116b046_ -components 1 -gzip 
[1] TRUE

Visualizing FA images

Using ortho2, we can visualize these FA maps:

Getting MD vlaues

Similar to getting FA maps, we can get mean diffusivity (MD) maps, read them into R, and visualize them using ortho2:

cat '/tmp/RtmpMOnBkd/file2377721d939.Bdouble' |  /tmp/RtmpsRfqHp/Rinst7ed24cd45286/rcamino/camino/bin/md -inputmodel dt -outputdatatype double > '/tmp/RtmpMOnBkd/file2376328affe.Bdouble'
/tmp/RtmpsRfqHp/Rinst7ed24cd45286/rcamino/camino/bin/voxel2image -inputfile /tmp/RtmpMOnBkd/file2376328affe.Bdouble -header /tmp/RtmpMOnBkd/4Ddwi_b1000.nii.gz -outputroot /tmp/RtmpMOnBkd/file2373f0cce1c_ -components 1 -gzip

Export DTs to NIfTI

Using camino_dt2nii, we can export the diffusion tensors into NIfTI files. We see the result is the filenames of the NIfTI files, and that they all exist (otherwise there’d be an errors.)

nifti_dt = camino_dt2nii(
  infile = model_fname, 
  inputmodel = "dt",
  header = img_fname, 
  gzip = TRUE
)
/tmp/RtmpsRfqHp/Rinst7ed24cd45286/rcamino/camino/bin/dt2nii -inputfile /tmp/RtmpMOnBkd/file2377721d939.Bdouble -header /tmp/RtmpMOnBkd/4Ddwi_b1000.nii.gz -inputmodel dt -outputroot /tmp/RtmpMOnBkd/file237181add6c_ -gzip 
stopifnot(all(file.exists(nifti_dt)))
print(nifti_dt)
[1] "/tmp/RtmpMOnBkd/file237181add6c_exitcode.nii.gz"
[2] "/tmp/RtmpMOnBkd/file237181add6c_lns0.nii.gz"    
[3] "/tmp/RtmpMOnBkd/file237181add6c_dt.nii.gz"

We can read these DT images into R again using readnii, but we must set drop_dim = FALSE for diffusion tensor images because the pixel dimensions are zero and readnii assumes you want to drop “empty” dimensions

dt_imgs = lapply(nifti_dt, readnii, drop_dim = FALSE)