Number of Rotations (0054,0051) is the number of separate rotations. See Section C.8.4.12 for definition of a rotation. When Image Type (0008,0008), Value 3, is RECON TOMO, GATED TOMO or RECON GATED TOMO, then the Number of Rotations (0054,0051) shall be 1.
Rotation Vector (0054,0050) is an indexing vector. The value of the nth element of this vector is the rotation number of the nth frame in this image, and shall have a value from 1 to Number of Rotations (0054,0051).