- 00000018WIA3092F870GYZ
- id_400234051.4
- Mar 1, 2022 2:47:37 PM
Tensor filename
Use the user-defined Tensor filename User CV with Diffusion Tensor Imaging or DTI scans to set a custom diffusion tensor file. By setting the Tensor filename (CV11) to the number XXX, you can specify a custom tensor file (tensorXXX.dat) that is used instead of the product tensor.dat file. For example, setting CV11 to 476 makes the system read tensor476.dat for the diffusion gradient vectors.
Tensor files based on widely used diffusion encoding schemes in several multi-center clinical trials and neuroscience research projects are pre-loaded, see the following table:
| Study | Configuration on MR Operator Console | Diffusion Encoding Schemes |
|---|---|---|
| UK Biobank Brain Imaging* | Field strength: 3T
Advanced tab: CV11 - Tensor filename: 521 Diffusion tab: b-value: 2000 # of Diffusion Directions: 104 | # of Diffusion Directions: 104
|
| Field strength: 3T
Advanced tab: CV11 - Tensor filename: 1090 Diffusion tab: b-value: 2000 # of Diffusion Directions: 90 | # of Diffusion Directions: 90
| |
| ADNI-3 Advanced Protocols (Alzheimer’s Disease Neuroimaging Initiative)** | Field strength: 3T
Advanced tab: CV11 - Tensor filename: 1127 Diffusion tab: b-value: 2000 # of Diffusion Directions: 126 | # of Diffusion Directions: 126
The 126 vector version is the "classic" ADNI3 Advanced 3 shell set. It is nominally intended for scanners capable of gradient peak amplitude > 70 mT/m.
|
| Field strength: 3T
Advanced tab: CV11 - Tensor filename: 1127 Diffusion tab: b-value: 2000 # of Diffusion Directions: 126 | # of Diffusion Directions: 100
The 100 vector version is intended to support multishell scanning in a reasonable time on scanners with lower gradient peak amplitude.
| |
| ABCD (Adolescent Brain Cognitive Development) study*** | Field strength: 3T
Advanced tab: CV11 - Tensor filename: 4321 Diffusion tab: b-value: 3000 # of Diffusion Directions: 102 | # of Diffusion Directions: 102
|
| Human Connectome Project Lifespan**** | Field strength: 3T Advanced tab: CV11 - Tensor filename: 1225 Diffusion tab: b-value: 3000 # of Diffusion Directions: 198 | # of Diffusion Directions: 198
|
*https://www.fmrib.ox.ac.uk/ukbiobank/protocol/
**http://adni.loni.usc.edu/adni-3/
***https://abcdstudy.org/images/Protocol_Imaging_Sequences.pdf
****https://www.humanconnectome.org/study/hcp-lifespan-development/project-protocol/imaging-protocols-hcp-development
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You can employ other diffusion encoding schemes by defining the diffusion gradient vectors in a file named tensorXXX.dat and placing it in /srv/nfs/psd/usr/etc/.
Custom tensor files can be generated as single ASCII text file, consisting of diffusion gradient tables with one row per entry (i.e. per DWI volume), with each row consisting of tab/space-separated three floating-point values corresponding to [Frequency (X) Phase (Y) Slice (Z)] which are the components of the diffusion encoding gradient vector. The magnitude of diffusion gradient vectors should be 1 or less for multi-shell DTI (see below for scaling). Interspersed b0 or T2 (i.e. the magnitude of vector = 0) can be also specified in custom tensor files. There is a header entry for number of directions preceding each gradient table.
When you use a custom-tensor file, check that the number of diffusion directions input in the scan prescription matches with this header entry and length of the length of the diffusion encoding gradient table in the specified custom tensor file. It is recommended to use GE default tensor.dat file (/srv/nfs/psd/etc/), which contains diffusion gradient tables up to 300 directions, as a template and to update the entries to be customized.
For multi-shell DTI, a single gradient table is used as well with the gradient vectors for the inner shells scaled by the square root of the inner shell b-value to the outermost shell b-value. As an example, for two-shell DTI consisting of the inner shell with b-value of 1000 s/mm2 and the outer shell with b-value of 2000 s/mm2, the magnitude of diffusion gradient vectors for 2000 s/mm2 should be 1 and the magnitude of diffusion gradient vectors for 1000 s/mm2 should be sqrt(1000/2000)=0.7071. In a DTI scan employing such a multi-shell encoding scheme, the maximum b value should be prescribed in the scan prescription.
B-value is included in DICOM tags (0018, 9087 and 0043, 1039) and diffusion gradient vector is also included in DICOM header (Tags: 0019, 10BB (Frequency) - 0019, 10BC (Phase) - 0019, 10BD (Slice). The value of the Tensor filename (CV11) is included in DICOM tag (0019, 10B2)
This feature is intended to enable DTI data acquisition with a user-defined diffusion encoding scheme. You can only post-process this data on the system if you have a compatible post-processing application. Consult your applications specialist to determine if your system has a compatible post-processing application. The following applications are incompatible with DTI custom tensor file (CV11>0):
- FuncTool (all versions)*
- READY View DTI (Volume Viewer versions below 16.0 Ext 6)*
- BrainWave (versions below 3.3)
*These applications, or specific versions of these applications, do not provide error messages for attempting to load custom tensor file-based images.
In Research Mode, up to 1000 diffusion directions can be selected but the user would need to first ensure that the appropriate tensor file with user-defined set of diffusion gradient vectors has been installed in /srv/nfs/psd/usr/etc/ and the appropriate tensor filename has been input via User CV 11.