Help File

The program is to correct the distortions caused by field inhomogeneity and eddy current induced field because of strong diffusion weighting gradients in diffusion tensor imaging (DTI) datasets acquired by echo planar imaging (EPI). All input volumes should be Analyze format.

Calibration Tab

The calibration section takes field maps of the base volume and at least four field maps in non-coplanar diffusion weighing directions. The eddy current induced fields will be saved to a file.

· Raw Phase Map File

1. Select the radio button to activate the group box. Click the GE button to select the raw P file acquired by multi-echo phase volumes. The sequence is desribed in NeuroImage xxxxxx.

2. Click the Calibration button to save the eddy current induced gradient file.

· B0 and DW Field Maps

1. Select the radio button to activate the group box. Click Browse button to select field variation maps. The order of field map volume is b0, b1,b2,..., bn.

2. Click the Browse button in "ECIF Estimation with Orthogonal Base" to select the diffusion gradient directional scheme file. Each row in the scheme file contains the normalized diffusion direction. The order should match the field map volume order. An example of diffusion weighting directional scheme:

0.2160 -0.8986 0.3819

-0.4446 -0.4187 0.7918

-0.6352 -0.7701 -0.0595

0.5005 -0.1925 0.8440

-0.2212 0.5312 -0.8179

-0.8919 0.0791 -0.4452

… … …

3. Click the Calibrate button to save the eddy current induced field to disk.

Correct Tab

The correct section takes the DTI file, the base field map and optional calibrated eddy current induced field to correct the DTI file.

1. Click the browse button in DTI Input box to select the DTI dataset.

2. Click the browse button in B0 Map box to select the base field map.

3. If no eddy current induced field information, click the Correct button to correct the distorted DTI dataset without eddy current induced distortion correction.

4. If eddy current induced field exists, click the radio button.

5. Select the Calibration file and Diffusion Weighting Scheme. The scheme should have the same diffusion weighing order of the DTI dataset.

6. Input acquisition time in milliseconds.

7. Click Correct to correct the distortion caused by field inhomogeneity and eddy current induced field.