GRB files are plain text files containing gradient directions and b-values.
The format of a GRB file is as follows, demonstrated as an example here for a 6-direction + b0 scheme, each line having 3 entries, X Y Z:
FileVersion: 1
IncludeBValues: no
NrOfEntries: 7
X Y Z
0 0 0
0.577 0.577 0.577
-0.577 -0.577 0.577
0.577 -0.577 -0.577
-0.577 0.577 -0.577
0.707 0.707 0
0.707 0 0.707
If the b-values (1000 in this case) are included, the file looks like this: Note that Include BValues is changed to “yes”, and that each line now has 4 entries, X Y Z b:
FileVersion: 1
IncludeBValues: yes
NrOfEntries: 7
X Y Z b
0 0 0 0
0.577 0.577 0.577 1000
-0.577 -0.577 0.577 1000
0.577 -0.577 -0.577 1000
-0.577 0.577 -0.577 1000
0.707 0.707 0 1000
0.707 0 0.707 1000
FileVersion: 1
IncludeBValues: no
NrOfEntries: 31
X Y Z
0.0 0.0 0.0
1.0000000000 0.0000000000 0.0000000000
0.7703189794 -0.6334477240 0.0731618129
0.2561448687 -0.0249786863 0.9663156169
0.7976459349 -0.1068670680 0.5935826751
-0.4615578229 0.8761728334 0.1388723949
-0.2292204126 0.8533775040 -0.4681931632
-0.2630794898 -0.4113047154 -0.8727070603
0.7992449025 0.5854349684 0.1359171940
0.5067126566 0.5103287334 0.6948430524
0.3054330813 -0.1364364527 -0.9423883102
-0.7972741706 -0.1949622700 -0.5712649212
-0.8042542270 -0.5926021950 -0.0446964971
0.1865635668 0.9537832611 0.2355663949
-0.3881893823 0.1079319091 0.9152375137
-0.1339272628 0.6629447625 0.7365919699
-0.3384961835 -0.8809697404 0.3306246365
0.7673774759 0.3119018842 -0.5602222989
0.4065245350 -0.6656047592 0.6258658858
0.2871876223 -0.7612264361 -0.5814271946
-0.7661480348 0.4319864923 0.4758201964
-0.1793153505 -0.5264136055 0.8311045187
-0.7673768974 -0.3119020115 0.5602230203
0.2179780246 -0.9751760272 0.0389524925
0.4189866219 0.8397110024 -0.3454499142
0.1777380470 0.4786928124 -0.8598036857
-0.3397814897 -0.8554854208 -0.3907598163
-0.7844890989 0.5119797541 -0.3499336868
-0.4197498720 0.2604620840 -0.8694650929
0.7734515702 -0.3550403437 -0.5250895379
-0.9984481940 0.0477096943 0.0287226207