def __init__(self, folders, read_metadata=True, header_fields=None):
DicomFileSet.__init__(self,  folders)<EOL>self.read_dcm = self.get_dcm_reader(read_metadata, header_fields)<EOL>
:param folders: str or list of strs
Path or paths to folders to be searched for Dicom files

:param read_metadata: bool
If True, will make a list of DicomFiles, otherwise will store
a simple DICOM header (namedtuples) with the fields specified
in header_fields.

:param header_fields: set of strings
Set of header fields to be read from each DICOM file in a DicomHeader.
If store_metadata is False, this won't be used. Else and if this is
None, will store the whole DicomFile.