For PRC use only
Date of approval:
Signature of Chair:
Siemens Vision 1.5T Sequence Description
Sequence name: DTI v1.3, 1.4, and 1.55 – diffusion tensor imaging sequences
Developer: Jan Hrabe, NKI
Filenames:
dti_v13.ekc
dti_v14.ekc
dti_v15.ekc
Date: 4/24/2001
Location: /usr/appl/sequence/local
Other files: SPL source code file dti_v11.sph in the $EXT/local directory.
Brief description: These sequences are loosely based on the approved DTI sequence dti_v11.ekc,
the main characteristics are as follows:
1. Averaging is eliminated in favor of storing all images separately (e.g., 3 images for every
slice and b value if number of averages is set to 3).
2. SPL code (attached) is identical to the code for the dti_v11.ekc sequence; no further changes
were required.
3. All unnecessary Pargen code was eliminated to lower the board memory consumption and
thus increase maximum number of slices and b values.
4. Absolute b value in all these sequences is 1000.29 s/mm2, achieved with 20.8 mT/m absolute
gradient. TE is fixed to 99.96 ms, pacing the echo asymmetrically on line 25 out of 96
acquired. Resolution is fixed at 96x128 (interpolated to 128x128). The recommended TR is
longer than 6s with 3 averages. Reconstruction time is approximately 7-10 min (all slices).
Minimum slice thickness is 3 mm (limited by the short ramp time 300 s).
5. Sequence version 1.3 (code attached) uses 1 (b=0) + 6 b values with the directions identical
to version 1.1. These are: (0,0,0), (1,1,0), (1,0,1), (0,1,1), (1,-1,0), (-1,0,1), (0,1,-1) for
(phase, read, slice). Note that the phase encode direction may change with the angle of the
slice. Averaging loop is performed outside, that is, the sequence cycles first through slices,
then b values, and lastly averages. Up to 27 slices can be acquired.
6. Sequence version 1.4 (code attached) uses 1+8 b values. Their directions are based on Jones
DK, Horsfield MA, Simmons A: Optimal Strategies for Measuring Diffusion in Anisotropic
Systems by Magnetic Resonance Imaging (MRM 42:515-525, 1999), page 518, Table 2 with
(x, y, z) denoting (phase, read, slice), respectively. Up to 20 slices can be acquired.
7. Sequence version 1.5 (code attached) uses 1+6 b values but their directions are better
optimized than in version 1.3, again using the above mentioned MRM paper by Jones et al.
Up to 27 slices can be acquired.
8. Sequence 1.3 is intended for finishing current studies with almost unchanged parameters but
more slices and better motion control. Sequences 1.4 and 1.5 should be used for any new
studies.