Longitudinal Preprocessing#

Open image

Background#

Longitudinal preprocessing pipeline is designed to process longitudinal data with two or more sessions. Based on Reuter et al. 2012, all secions of subjects are first preprocessed independently and then a within-subject template is created by averaging all sessions of the subject. Subsequently the within-subject template is registered to standard space and all sections are then registered to the longitudinal template in standard space.

Configuring CPAC to Run Longitudinal Preprocessing Pipeline#

../_images/longitudinal.png

  1. Longitudinal - [On, Off]: Run longitudinal preprocessing pipeline or not. Default is Off.

  2. Average Method - [string]: Method to average longitudinal template. Default is median.

  3. DOF - [integer]: Transform degree of freedom in flirt. Default is 12.

  4. Interpolation - [string]: Interpolation in flirt. Default is trilinear.

  5. Cost Function - [string]: Cost function in flirt. Default is corratio.

  6. Thread Pool - [integer]: Number of threads in a thread pool. More threads can speed up the longitudinal template creation process. Default is 2.

  7. Convergence Threshold - [integer]: Convergence threshold of longitudinal template. Default is -1, which uses numpy.finfo(np.float64).eps.

Configuration Without the GUI#

The following nested key/value pairs will be set to these defaults if not defined in your pipeline configuration YAML.

longitudinal_template_generation:

  # If you have multiple T1w's, you can generate your own run-specific custom
  # T1w template to serve as an intermediate to the standard template for
  # anatomical registration.

  # This runs before the main pipeline as it requires multiple T1w sessions
  # at once.
  run: Off

  # Freesurfer longitudinal template algorithm using FSL FLIRT
  # Method to average the dataset at each iteration of the template creation
  # Options: median, mean or std
  average_method: median

  # Degree of freedom for FLIRT in the template creation
  # Options: 12 (affine), 9 (traditional), 7 (global rescale) or 6 (rigid body)
  dof: 12

  # Interpolation parameter for FLIRT in the template creation
  # Options: trilinear, nearestneighbour, sinc or spline
  interp: trilinear

  # Cost function for FLIRT in the template creation
  # Options: corratio, mutualinfo, normmi, normcorr, leastsq, labeldiff or bbr
  cost: corratio

  # Number of threads used for one run of the template generation algorithm
  thread_pool: 2

  # Threshold of transformation distance to consider that the loop converged
  # (-1 means numpy.finfo(np.float64).eps and is the default)
  convergence_threshold: -1

References#

Martin Reuter, Nicholas J.Schmansky, H. Diana Rosas, Bruce Fischl. Within-subject template estimation for unbiased longitudinal image analysis. Neuroimage. 2012 July 16; 61(4): 1402–1418. doi:10.1016/j.neuroimage.2012.02.084.