How can I get properties of a Linq To SQL object without getting the navigation properties?

Expanding on this answer I came up with the following to dump a Linq to SQL query into a csv format:

Public Shared Function ObjectsToCsvData(ByVal objs As IEnumerable(Of Object)) As String
    If objs Is Nothing Then
        Throw New ArgumentNullException("obj", "Value can not be null or Nothing!")
    End If

    Dim sb As StringBuilder = New StringBuilder()
    Dim firstObj As Object = objs.First
    Dim t As Type = firstObj.[GetType]()
    Dim pi As PropertyInfo() = t.GetProperties(BindingFlags.DeclaredOnly Or BindingFlags.Public Or BindingFlags.Instance)
    For index As Integer = 0 To pi.Length - 1
        If Not pi(index).GetAccessors()(0).IsVirtual Then
            sb.Append(pi(index).Name)
            sb.Append(",")
        End If
    Next
    sb.Remove(sb.Length - 1, 1)
    sb.Append(vbCrLf)
    For Each obj As Object In objs
        For index As Integer = 0 To pi.Length - 1
            If Not pi(index).GetAccessors()(0).IsVirtual Then
                sb.Append(pi(index).GetValue(obj, Nothing))
                sb.Append(",")
            End If
        Next
        sb.Remove(sb.Length - 1, 1)
        sb.Append(vbCrLf)
    Next
    Return sb.ToString()
End Function

Problematically, this includes all the navigation properties as columns. Is there an easy way to exclude the related objects? I had hoped that the check for virtual properties would do it:

If Not pi(index).GetAccessors()(0).IsVirtual Then...

but I think I am confusing this with EF.