DTI:Acquisition
Definition of DTI Protocols
Work is ongoing to define DTI acquisition protocols that can be used in single and multi-site trials. This work is being informed by the DTI calibration studies performed by the JHU group.
Basic Steps for Processing DTI data
If required, convert data from the original format to another file format that your software accepts. Some common ones are:
- Digital Imaging and Communications in Medicine (DICOM) - all scanners that I know of support DICOM, but one must be aware that there are variations in the way that DWI information is stored and important information may be stored in the vendors private fields. The relevant fields for DWI are:
- 0018 9075 CS 1 Diffusion Directionality
- 0018 9076 SQ 1 Diffusion Gradient Direction Sequence
- 0018 9087 FD 1 Diffusion b-value
- 0018 9089 FD 3 Diffusion Gradient Orientation
- 0018 9117 SQ 1 MR Diffusion Sequence
- 0018 9147 CS 1 Diffusion Anisotropy Type
Note that while there are tags for the gradient orientation and b-value there is not a tag for the entire b matrix. Also notice that the vendor-specific measurement frame is also not stored - essentially you need to know the relationship between the coordinate frame in which the gradient directions are defined and the coordinate frame in which the image orientation is defined or your color maps will not be correct. Since, one usually doesn't know these coordinate frames, one must resort to flipping the sign of various gradient direction components until the directions given by the tensor processing correspond to what you know from the anatomy. The NA-MIC group has also noted that GE has stored the gradient directions, not in the tag assigned to that quantity, but in other fields. Siemens (as of 2006) stores the b-matrix as well as other diffusion information.
See here for more information about the format of DTI data as it is acquired by each of the dominant MR scan manufacturers. Learn more about DICOM here.
