# C.8.9.4.1.9 Image Index

Image Index (0054,1330) is an index identifying the position of this image within a PET Series.

Note: The scheme for encoding Image Index (0054,1330) is as follows. Images within a PET Series can be viewed as a multi-dimensional array whose possible dimensions include R-R Intervals, Time Slots, Time Slices, and Slices. The dimensions of the array are defined by the Series Type (0054,1000) Value 1. Each dimension of the array has an index that identifies the position of this image in the array. The indices are: R-R Interval Index, Time Slot Index, Time Slice Index, Slice Index. The indices are calculated as follows:

 Index Range of Index Order of Images along that Dimension R-R Interval Index 1 to Number of R-R Intervals (0054,0061) Increasing Low R-R Value (0018,1081) Time Slot Index 1 to Number of Time Slots (0054,0071) Increasing Trigger Time (0018,1060) Time Slice Index 1 to Number of Time Slices (0054,0101) Increasing Frame Reference Time (0054,1300) Slice Index 1 to Number of Slices (0054,0081) If Series Type (0054,1000) Value 2 is IMAGE: Order is in increasing position along the normal, where the normal is determined by the cross product of the direction cosines of the row and column of the image. See Image Orientation (0020,0037) in the Image Plane Module. If Series Type (0054,1000) Value 2 is REPROJECTION: Order is in increasing or decreasing angle of the normal, where the normal is determined by the cross product of the direction cosines of the row and column of the image. See Image Orientation (0020,0037) in the Image Plane Module. (Note that reprojection images rotate about only a single axis as described in C.8.9.1.1.1. Therefore, all normals are co-planar and make a single angle with respect to each other.)

Using these index values the position of this image within the multi-dimensional array (the Image Index (0054,1330)) is calculated as follows:

 Series Type (0054,1000), Value 1 Dimensions of Array (Last dimension is most rapidly changing) Encoding of Image Index (0054,1330) STATIC Slice Slice Index WHOLE BODY Slice Slice Index DYNAMIC Time Slice \ Slice ( ( Time Slice Index - 1 ) * ( Number of Slices (0054,0081) ) ) + Slice Index GATED R-R Interval \ Time Slot \ Slice ( ( R-R Interval Index - 1 ) * ( Number of Time Slots (0054,0071) ) * ( Number of Slices (0054,0081) ) ) + ( ( Time Slot Index - 1 ) * ( Number of Slices (0054,0081) ) ) + Slice Index