Like all indices in DicomObjects, this is 1-based - i.e. the range is from 1 to FrameCount.
If set to a value higher than FrameCount, this property is reduced modulo FrameCount, to bring it within range.  Cine sequences may therefore be run repeatedly simply by incrementing Frame continuously. Alternatively, to allow multi-frame images to “play” autonomously, the CineMode property may be used.

Frame only returns sensible values for images up to 32k frames – for larger images use LongFrame.

DicomImage Object  | DicomImage Members