'Einige Testdaten
dt.Columns.Add("Date", GetType(Date))
dt.Columns("Date").AllowDBNull = True
 
With dt.Rows
   .Add(CDate("1.1.2010"))
   .Add(DBNull.Value)
   .Add(CDate("1.1.2012"))
   .Add(CDate("1.2.2012"))
End With
 
'Eine bedingte Abfrage
Dim lst As List(Of Date) = _
    (From x As Object In dt.Rows
     Select ddtr = CType(x, DataRow)("Date")
     Where (Not IsDBNull(ddtr) AndAlso _
       CType(ddtr, Date) > CDate("1.1.2011"))
     Select CType(ddtr, Date)).ToList