An invitation letter from you. PLEASE NOTE: This form is for requesting your visa invitation letter only.I would like to invite you to the United States of America to stay with us for three months. It would be very nice to have you with us. The deadline to request a Letter of Invitation is November 1st. Complete one form per attendee, and be sure to include all required information. To help secure your visa to Chicago, you can use our downloadable form to create a personalized invitation letter to the RSNA annual meeting.