Hi Sui,
if you replace T with string, you will get the original patient name string from the DICOM message (e.g. "Doe^John"), whereas if you replace T with DicomPersonName, you will be able to access the individual name parts from the result. So it is mainly a question of what you prefer.
The Get overrides typically support casts to basic types, so generally it is sufficient to replace T with basic types or arrays such as string, int, double, string[], int[], double[].
Regards,
Anders @ Cureos