No, I have not used it before, thank you for information. 

I can not use it with -grad option. Without -grad option mrinfo's output is;

erdem@erdem-virtual-machine:~/Documents/mrtrix-read-only$ mrconvert /home/erdem/Desktop/Test/DICOM/12032816 ./out_img.nii.gz

mrconvert: scanning DICOM set "/home/erdem/Desktop/Test/DICOM/12032816"  - ok

Select series ('q' to abort):

   0 -  176 MR images 16:21:28 t1_mpr_sag_iso (*tfl3d1_ns) [2]

   1 -   62 MR images 16:23:13 ep2d_diff_mddw_30_p2 (*ep_b1000#5) [3]

   2 -   45 MR images 16:29:31 ep2d_diff_mddw_30_p2_ADC (*ep_b0_1000) [4]

   3 -   45 MR images 16:29:31 ep2d_diff_mddw_30_p2_TRACEW (*ep_b1000t) [5]

   4 -   45 MR images 16:29:31 ep2d_diff_mddw_30_p2_FA (*ep_b0_1000) [6]

   5 -   45 MR images 16:29:32 ep2d_diff_mddw_30_p2_ColFA (?) [7]

   6 -   72 MR images 16:30:41 gre_field_mapping (*fm2d2r) [9]

   7 -   36 MR images 16:30:41 gre_field_mapping (*fm2d2r) [10]

   8 -  113 MR images 16:32:40 ep2d_pace_dynt_moco 103 (*epfid2d1_64) [11]

   9 -  113 MR images 16:32:40 act_MoCoSeries (*epfid2d1_64) [12]

  10 -    1 MR images 16:37:32 Design (*epfid2d1_64) [13]

  11 -    1 MR images 16:37:32 EvaSeries_GLM (*epfid2d1_64) [14]

  12 -    3 MR images 16:37:32 Mean_&_t-Maps (*epfid2d1_64) [15]

  13 -  179 MR images 16:39:53 ep2d_tra_pasl_p2 140 (*epfid2d1_64) [16]

  14 -  179 MR images 16:39:53 MoCoSeries (*epfid2d1_64) [17]

  15 -    1 MR images 16:46:17 Perfusion_Weighted (*epfid2d1_64) [18]

  16 -    1 MR images 16:46:17 relCBF (*epfid2d1_64) [19]

? 1

mrconvert: reading DICOM series "ep2d_diff_mddw_30_p2"... 100%

mrconvert: DICOM image contains multiple frames - reformating... 100%

mrconvert: copying data... 100%

erdem@erdem-virtual-machine:~/Documents/mrtrix-read-only$ mrinfo -grad out_img.nii.gz 

mrinfo: expected at least 1 arguments (0 supplied)

erdem@erdem-virtual-machine:~/Documents/mrtrix-read-only$ mrinfo -grad ./out_img.nii.gz 

mrinfo: expected at least 1 arguments (0 supplied)

erdem@erdem-virtual-machine:~/Documents/mrtrix-read-only$ mrinfo  ./out_img.nii.gz 

************************************************

Image:               "./out_img.nii.gz"

************************************************

  Format:            NIfTI-1.1

  Dimensions:        128 x 128 x 45 x 62

  Voxel size:        2 x 2 x 2 x ?

  Dimension labels:  0. left->right (mm)

                     1. posterior->anterior (mm)

                     2. inferior->superior (mm)

                     3. undefined (?)

  Data type:         unsigned 16 bit integer (little endian)

  Data layout:       [ +0 +1 +2 +3 ]

  Data scaling:      offset = 0, multiplier = 1

  Comments:          Kirkar Ali Emir (2

                     study: EGE BEYIN; DOB: 04/02/2003; DOS: 28/03/2012 16:23:13

  Transform:               0.9975   6.938e-08    -0.07125      -126.6

                        -0.002623      0.9993    -0.03672      -142.7

                           0.0712     0.03681      0.9968      -41.47

                                0           0           0           1

erdem@erdem-virtual-machine:~/Documents/mrtrix-read-only$ 

So how should I progress?