eg:
string previousImageAquisitionFolder = ""; // System.IO.Path.GetDirectoryName(od.FileName) ?? "");
Application.UserAppDataRegistry.CreateSubKey("previousImageAquisitionFolder");
previousImageAquisitionFolder =(Application.UserAppDataRegistry.GetValue("previousImageAquisitionFolder")?? "").ToString();
Application.UserAppDataRegistry.SetValue("previousImageAquisitionFolder",previousImageAquisitionFolder