Revision as of 15:28, 16 April 2012

Documentation

All CNP DTI processing and quality assurance is documented in the CNP DTI QA Google Document. To view and edit the document, request access from Katie Karlsgodt or Anna Xu.

Scripts

dti_proc.sh is a script written by Russ Poldrack to preprocess the raw CNP DTI data. The path for the script is /space/raid2/data/poldrack/CNP/scripts/dti_proc.sh. The usage is dti_proc <input directory path>.

An alternate version exists called dti_proc_regressor. The difference between the two versions is that the regressor script contains a nuisance regressor based on the Galachan, 2010 paper, that can to some extent correct for vibration artifacts. This artifact exists on BMC data before Fall 2010. After Fall 2010 the table was bolted down, correcting the artifact. The CCN table was bolted at installation, thus avoiding the artifact entirely. Unfortunately it does not entirely correct the issue, so the shareable data uses the original version of the script with people who show the artifact marked for elimination.

Processing

The dti_proc_regressor script processes the data using FSL Diffusion Toolbox (FDT).

Steps:
1. B0 image is skull stripped, creating B0_image_brain
2. the raw data are registered to the first (B0) image using mcflirt- this both corrects for eddy currents and helps motion, the resulting file is dti_mcf
3. dtifit is run, creating FA, L1, L2, MD and other processed images in subject space
4. the FA and color maps are registered to MNI space (FA2std and V12std).
5. Generic ROIs from the JHU atlas are applied to the FA image in standard space.

WARNING- the resulting values are NOT to be used as data, rather just as first pass markers for scan integrity. They are not well registered enough to be used for anything, as evidenced by the low FA values.

6. Motion is calculated
7. bvecs and bvals for each subject are compared to the CNP standards.

NOTE: there are different bvecs and bvals for subjects on the CCN and BMC scanners, as well as for a subset of subjects scanned during the transition and intial set up of the CCN

7. a pdf is generated (dti_diag.pdf)

Quality Control

The checking procedures for CNP follow the Cannon Lab DTI QA Protocol, which was adapted from procedures in Paul Thompson's lab. This can be found at: Cannon_Lab_Processing_and_QA

The additional QA script is located at /space/raid2/data/poldrack/CNP/scripts/DTI_QA.sh

This script creates a small text file to be used in QA. If the script runs properly it:
1. matches bvals and bvecs
2. calculates mean in-mask FA and MD
3. calculates motion in each direction
4. creates a standard deviation file for regular and mcf images
5. uses regional masks to calculate the percentage of cropped voxels in the occipital lobe, frontal lobe, superior region, temporal lobes and cerebellum.

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