Dear Thomas,



just want to remind everyone that _normally_ you don’t need to worry about getting the readout time right. There are only a few cases in which is important



1. If you want to combine topup-derived fields and fieldmap-style analysis (for example derive field from topup and unwarp data using fugue).

2. If you want to combine data with different readout times in a single analysis (and even then it is only their ratio that is important to get right).

3. If you have a particular interest in the field itself, rather than just wanting to use it to unwarp images.



My guesstimate is that for 99% of all uses of topup/eddy one doesn’t need to get that number right. And for those cases I recommend just using 0.05.



Jesper





> On 18 Jan 2018, at 21:05, Thomas DeRamus <[log in to unmask]> wrote:

> 

> Its one of the diffusion sequences from the FBIRN dataset (UC Irvine I believe).

> 

> The rest of the Siemens-scanner datasets don't do this so this comes as a surprise.

> 

> Here's some of the information from the header. If there's anything else I can provide please let me know.

> 

> 0018 0020        2 [1366    ] //          ACQ Scanning Sequence//EP

> 0018 0021        6 [1376    ] //           ACQ Sequence Variant//SK\SP

> 0018 0022        6 [1390    ] //               ACQ Scan Options//PFP\FS

> 0018 0023        2 [1404    ] //       ACQ MR Acquisition Type //2D

> 0018 0024        6 [1414    ] //              ACQ Sequence Name//*ep_b0

> 0018 0025        2 [1428    ] //                 ACQ Angio Flag//N

> 0018 0050        2 [1438    ] //            ACQ Slice Thickness//2

> 0018 0080        4 [1448    ] //            ACQ Repetition Time//9000

> 0018 0081        2 [1460    ] //                  ACQ Echo Time//84

> 0018 0083        2 [1470    ] //         ACQ Number of Averages//1

> 0018 0084       10 [1480    ] //          ACQ Imaging Frequency//123.253287

> 0018 0085        2 [1498    ] //             ACQ Imaged Nucleus//1H

> 0018 0086        2 [1508    ] //                ACQ Echo Number//1

> 0018 0087        2 [1518    ] //    ACQ Magnetic Field Strength//3

> 0018 0088        2 [1528    ] //     ACQ Spacing Between Slices//2

> 0018 0089        2 [1538    ] //ACQ Number of Phase Encoding Steps//96

> 0018 0091        2 [1548    ] //          ACQ Echo Train Length//1

> 0018 0093        4 [1558    ] //           ACQ Percent Sampling//100

> 0018 0094        4 [1570    ] //ACQ Percent Phase Field of View//100

> 0018 0095        4 [1582    ] //            ACQ Pixel Bandwidth//1563

> 0018 1000        6 [1594    ] //       ACQ Device Serial Number//35044

> 0018 1020       12 [1608    ] //           ACQ Software Version//syngo MR B17

> 0018 1030       10 [1628    ] //              ACQ Protocol Name//fbirn_dti

> 0018 1251        4 [1646    ] //          ACQ Transmitting Coil//Body

> 0018 1310        8 [1658    ] //         ACQ Acquisition Matrix// 128 0 0 128

> 0018 1312        4 [1674    ] //   ACQ Phase Encoding Direction//COL

> 0018 1314        2 [1686    ] //                 ACQ Flip Angle//90

> 0018 1315        2 [1696    ] //        ACQ Variable Flip Angle//N

> 0018 1316       16 [1706    ] //                        ACQ SAR//0.68472755387451

> 0018 1318        2 [1730    ] //                      ACQ DB/DT//0

> 0018 5100        4 [1740    ] //           ACQ Patient Position//HFS

> Group: 0019, Length:      854

> 0019 0010       18 [1752    ] //                               //hex OB: (len 8)53 49 45 4d 45 4e 53 20

> 0019 1008       12 [1778    ] //                               //hex OB: (len 8)49 4d 41 47 45 20 4e 55

> 0019 1009        4 [1798    ] //                               //hex OB: (len 4)31 2e 30 20

> 0019 100a        2 [1810    ] //                               //hex OB: (len 2)48 00

> 0019 100b        4 [1820    ] //                               //hex OB: (len 4)33 32 2e 35

> 0019 100c        2 [1832    ] //                               //hex OB: (len 2)30 20

> 0019 100d       12 [1842    ] //                               //hex OB: (len 8)44 49 52 45 43 54 49 4f

> 0019 100f        4 [1862    ] //                               //hex OB: (len 4)46 61 73 74

> 0019 1011        2 [1874    ] //                               //hex OB: (len 2)4e 6f

> 0019 1012       12 [1884    ] //                               //hex OB: (len 8)00 00 00 00 00 00 00 00

> 0019 1013       12 [1904    ] //                               //hex OB: (len 8)00 00 00 00 00 00 00 00

> 0019 1014        6 [1924    ] //                               //hex OB: (len 6)30 5c 30 5c 30 20

> 0019 1015       24 [1938    ] //                               //hex OB: (len 8)00 00 00 00 00 00 92 c0

> 0019 1016        6 [1970    ] //                               //hex OB: (len 6)34 2e 35 31 37 35

> 0019 1017        2 [1984    ] //                               //hex OB: (len 2)31 20

> 0019 1018        4 [1994    ] //                               //hex OB: (len 4)32 35 30 30

> 0019 1028        8 [2006    ] //                               //hex OB: (len 8)fa 7e 6a bc 74 b3 35 40

> 0019 1029      576 [2022    ] //                               //hex OB: (len 8)00 00 00 00 80 a5 b1 40

> Group: 0020, Length:      330

> 0020 0011        2 [2746    ] //              REL Series Number//21

> 0020 0012        2 [2756    ] //         REL Acquisition Number//1

> 0020 0013        2 [2766    ] //            REL Instance Number//1

> 0020 0032       40 [2776    ] //     REL Image Position Patient//-1152\-1148.8038740158\-32.113800048828

> 0020 0037       12 [2824    ] //REL Image Orientation (Patient)//1\0\0\0\1\0

> 0020 0052       52 [2844    ] //     REL Frame of Reference UID//1.3.12.2.1107.5.2.32.35044.1.20110827075323000.0.0.0

> 0020 1040        0 [2904    ] //REL Position Reference Indicator//

> 0020 1041       16 [2912    ] //             REL Slice Location//-32.113800048828