ListBox doesn't notice the new item added

Hi there,

XAML (ListBox)

<ListBox Name="Llistaimatges" ItemsSource="{Binding}"
 MouseDoubleClick="ListBox_MouseDoubleClick" Grid.ColumnSpan="4" Margin="205,10,33,91" Grid.RowSpan="2"  />

Code-behind:

Public Class GestorDocumental

Public robotImages As New List(Of BitmapImage)()

Public Function LoadImages() As List(Of BitmapImage)


        Dim robotImageDir As New DirectoryInfo("C:\puesto\Cuadro_de_Mando\GIT\Imagenes\Esquemas")

        For Each robotImageFile As FileInfo In robotImageDir.GetFiles("*.png")
            Dim uri As New Uri(robotImageFile.FullName)
            robotImages.Add(New BitmapImage(uri))
        Next
        Return robotImages
    End Function

And I'm using this event for add a new item (image) selected for the user:

robotimatges is a public member of the class.

Private Sub RadioButton_Checked(sender As Object, e As RoutedEventArgs)
        Dim dialogCercar As New System.Windows.Forms.OpenFileDialog
        dialogCercar.Filter = "JPEG Files (*.jpeg)|*.jpeg|PNG Files (*.png)|*.png|JPG Files (*.jpg)|*.jpg|GIF Files (*.gif)|*.gif"
        dialogCercar.ShowDialog()  Dim uri As New Uri(dialogCercar.FileName)
        robotImages.Add(New BitmapImage(uri))
    End Sub

Any help would be greatly appreciated!!

Primary platform is Windows 7 Ultimate 64 bit along with VS 2012/Sql2k8 for WPF/SilverLight projects.