Update an UpdatePanel when ModalDialog closes or on button event

I have two pages. The first one has one button and an UpdatePanel that contains an image. The button uses the following code to show a ModalDialog:

window.showModalDialog('AjustarImagem.aspx',
                                        null,
                                       'status:no;
                                        LOCATION: NO;
                                        TOOLBAR=NO ;
                                        DIRECTORIES: NO;
                                        dialogWidth:250px;
                                        dialogHeight:300px;
                                        dialogHide:true;
                                        help:no;
                                        scroll:yes');
                                        return false;");

What I need to do is to update the UpdatePanel when the ModalDialog closes, or when the click event of the ModalDialog button fires.