Which pick function should i used in DICOMImageSeries?

I try to use picker in ImageViewer2 which reade seriesof DICOMImage.
But It seems picker->pick not work as the return value by pick is always zeor.
The example I follow is using a 2d Image, while DICOMImage is a Series.
So I wonder which of picker and pick function should i used when read a 2D (not 2d) Image?