Report parameter hide/show query, in MS SSRS Reporting Web Service 2010

I want to query the hide/show status of parameters of a report. But it seems there is no property that tells that.

I used reporting service 2010, not reportviewer control. http://msdn.microsoft.com/en-us/library/reportservice2010.itemparameter.aspx

Below is my code:

public class ReportingService
  {
   private ReportingService2010 reportingService = null;

   public ReportingService()
   {
    reportingService = new ReportingService2010();
    reportingService.Credentials = CredentialCache.DefaultCredentials;
   }

    internal IList<ReportParameter> GetReportParameter(string reportUrl)
   {
    string historyId = null;
    bool forRendering = false;
    ParameterValue[] values = null;
    DataSourceCredentials[] credentialses = null;
    ItemParameter[] parameters = null;

    try
    {

     parameters = reportingService.GetItemParameters(reportUrl, historyId, forRendering, values, credentialses);

     foreach (var parameter in parameters)
     {
      //parameter.Name;
      //parameter.Prompt;
      //parameter.DefaultValues.FirstOrDefault();


//Problem:
 //how to get the show/hide status of the parameer.
 //the PromptUser retursn true only when both hide and prompt are false. but when hide is true, it return true.

 //The rdl is editted via IE. It can be also editted via BI, and others.


     }
     return reportParameters;

    }catch(SoapException e)
    {
     throw;
     //e.Detail.InnerXml.ToString()
    }
   }


  }