[Mristudio-users] 2 questions

[Dorian P.]

Hi everybody, and thank you for previous answers.

I have two questions today. First, I am comparing the gradient table
obtained by PAR/REC and DICOM files. They are very different, I can't find
similar lines. However, the final statistics on fiber tracking look
similar. Below you can find the two gradient tables and the fiber
statistics. Can you please tell me whether the difference in gradient
tables is normal, and if one is more precise than the other (the PAR/REC
table was calculated by a Matlab script developed at the John Hopkins).

Second question: Given a fixed time is available on a 1.5T, is it better to
obtain 2 scans of 16 directions or one scan of 32 directions? I can imagine
the SNR is much better with two, but not sure whether more directions
compensate for SNR too.

Thank you.
Dorian


Gradient table calculated from Philips PAR file:

0: -0.44136, -0.57117, -0.69207
1: -0.56394, -0.42335, 0.70905
2: 0.69797, -0.70323, 0.13526
3: -0.59198, -0.34304, -0.72931
4: -0.15274, -0.74584, -0.64838
5: 0.074435, -0.77687, -0.62525
6: 0.47574, -0.63875, -0.60471
7: 0.74718, -0.22799, -0.62429
8: -0.5922, -0.34308, -0.7291
9: -0.24242, -0.7705, -0.58954
10: 0.34275, -0.76982, -0.53843
11: 0.56981, -0.55721, -0.60402
12: 0.75753, -0.35855, -0.54552
13: -0.66312, -0.52489, -0.53364
14: -0.43153, -0.75822, -0.48876
15: 0.59311, -0.69541, -0.40574
16: 0.74571, -0.52489, -0.41038
17: -0.71084, -0.70326, 0.011793
18: -0.75432, -0.41491, 0.50878
19: 0.65451, -0.41491, 0.63204
20: 0.41865, -0.64824, 0.63602
21: -0.71152, -0.70239, 0.019779
22: -0.69363, -0.35558, 0.62645
23: -0.71454, -0.69646, 0.066208
24: -0.354, -0.63595, 0.68575
25: 0.22954, -0.63595, 0.7368
26: 0.69727, -0.70239, 0.14303
27: 0.64596, -0.224, 0.72977
28: -0.71425, -0.69728, 0.060467
29: -0.033138, -0.62847, 0.77712
30: 0.69693, -0.70198, 0.14667
31: 0.64313, 0.073913, 0.76219
32: 0, 0, 0
33: 100, 100, 100





Gradient table obtined by DICOM file:

0: 0.000000, 0.000000, 0.000000, 0.000000
1: -0.499998, -0.499998, -0.707110, 850.000000
2: -0.499998, -0.499998, 0.707110, 850.000000
3: 0.707107, -0.707107, 0.000000, 850.000000
4: -0.653288, -0.270606, -0.707098, 850.000000
5: -0.208664, -0.675630, -0.707095, 850.000000
6: 0.019658, -0.706829, -0.707112, 850.000000
7: 0.421225, -0.567950, -0.707109, 850.000000
8: 0.689925, -0.154927, -0.707108, 850.000000
9: -0.653495, -0.270675, -0.706880, 850.000000
10: -0.292882, -0.707102, -0.643604, 850.000000
11: 0.294515, -0.706411, -0.643619, 850.000000
12: 0.514993, -0.486072, -0.706056, 850.000000
13: 0.707102, -0.292882, -0.643604, 850.000000
14: -0.707102, -0.472486, -0.526084, 850.000000
15: -0.472486, -0.707102, -0.526084, 850.000000
16: 0.555492, -0.643950, -0.526077, 850.000000
17: 0.707102, -0.472486, -0.526084, 850.000000
18: -0.707107, -0.707107, -0.000212, 850.000000
19: -0.707102, -0.472486, 0.526084, 850.000000
20: 0.707102, -0.472486, 0.526084, 850.000000
21: 0.472486, -0.707102, 0.526084, 850.000000
22: -0.707085, -0.707085, 0.007849, 850.000000
23: -0.636392, -0.425181, 0.643604, 850.000000
24: -0.706047, -0.706047, 0.054730, 850.000000
25: -0.292882, -0.707102, 0.643604, 850.000000
26: 0.292882, -0.707102, 0.643604, 850.000000
27: 0.707085, -0.707085, 0.007849, 850.000000
28: 0.707102, -0.292882, 0.643604, 850.000000
29: -0.706260, -0.706260, 0.048932, 850.000000
30: 0.034719, -0.706256, 0.707105, 850.000000
31: 0.707060, -0.707060, 0.011526, 850.000000
32: 0.707107, -0.000000, 0.707107, 850.000000
33: 100.000000, 100.000000, 100.000000, 850.000000

Fiber statistics for each:
http://img580.imageshack.us/img580/2887/capturenbh.jpg
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