[Mristudio-users] ask for help on Philips AcHieva 1.5 T scanner gradient table

[susumu mori]

There are four potential types of the 15-orientation table of Philips.

1) The b0 image (i.e. 0, 0, 0) could be at the beginning or second from the
last. You can see images and figure out where is b0.
So your table is one type and other alternative is;

0:   1.0,  0.0,  0.0

 1:   0.0,  1.0,  0.0

 2:   0.0,  0.0,  1.0

 3:   -0.1789,  -0.1113,  -0.9776

 4:   -0.0635,  0.3767,  -0.9242

 5:   0.710,  0.0516,  -0.7015

 6:   0.6191,  -0.4385,  -0.6515

 7:   0.2424,  0.7843,  -0.5710

 8:   -0.2589,  -0.6180,  -0.7423

 9:   -0.8169,  0.1697,  -0.5513

 10:   -0.8438,  0.5261,  -0.1060

 11:   -0.2626,  0.9548,  -0.1389

 12:   0.0001,  0.9689,  0.2476

 13:   0.7453,  0.6663,  0.0242

 14:   0.9726,  0.2317,  0.0209

 15:   0,    0,    0

 16:   100, 100, 100

2) There is gradient overplus and non-overplus option. The one you used is
"non-overplus".

If you used overplus in your image protocol, it should be;

0: 0, 0, 0

1: -0.500, -0.500, -0.707

2: -0.500, -0.500, 0.707

3: 0.707, -0.707, 0.000

4: -0.110, -0.707, -0.699

5: 0.289, -0.700, -0.653

6: 0.627, -0.331, -0.705

7: 0.657, -0.273, -0.702

8: -0.673, -0.542, -0.504

9: 0.704, -0.491, 0.513

10: -0.693, -0.253, 0.675

11: -0.707, -0.707, 0.028

12: -0.282, -0.707, 0.648

13: 0.289, -0.702, 0.651

14: 0.706, -0.706, 0.054

15: 0.701, -0.205, 0.683

16: 100, 100, 100

Again, you have alternative choice of b0 at the second from the last.


If you find out that you used the "overplus" option, you have to be very
careful because you have to perform gradient re-calculation if you used
oblique imaging. For example, if you do plain axial imaging, you are fine.
However, if you tilted the axial plane to adjust the head orientation, the
gradient table has to be also tilted. If you used "non-overplus", this
table reorientation is performed on-the-fly but that's not the case for the
overplus. So, stay away from overplus.


On Thu, Jul 4, 2013 at 1:23 AM, 罗璐娇 <lujiaoluo1990 at 126.com> wrote:

> Hello experts,
> I was using dti studio to process my diffusion data obtained from Philips AcHieva
> 1.5 T scanner(medium angular, format: DICOM, in total of 17 images) .
>
> I used the pre-defined gradient table in dti studio listed below, while
> plus the 16th line to exclude the last average image
> 0:   0,    0,    0
> 1:   1.0,  0.0,  0.0
> 2:   0.0,  1.0,  0.0
> 3:   0.0,  0.0,  1.0
> 4:   -0.1789,  -0.1113,  -0.9776
> 5:   -0.0635,  0.3767,  -0.9242
> 6:   0.710,  0.0516,  -0.7015
> 7:   0.6191,  -0.4385,  -0.6515
> 8:   0.2424,  0.7843,  -0.5710
> 9:   -0.2589,  -0.6180,  -0.7423
> 10:   -0.8169,  0.1697,  -0.5513
> 11:   -0.8438,  0.5261,  -0.1060
> 12:   -0.2626,  0.9548,  -0.1389
> 13:   0.0001,  0.9689,  0.2476
> 14:   0.7453,  0.6663,  0.0242
> 15:   0.9726,  0.2317,  0.0209
> 16:    100    100    100
>
> But resulting images were not that fine, and couldn't distinguish the
> fiber orientations clearly. I tried to use mricron (dcm2niigue.exe) to
> obtain the bvecs and bvals file. But it also doesn't work.
> Would you please tell me how to solve this problem?
>
> Thanks so much!
>
>
>
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