window back in 1995 showing benefit of patients treated up to three hours and subsequent studies that have looked at later time windows have not been as positive as I said there was a big European study that showed benefit to four and a half so we don't like to street stroke based on time because everybody's brain is differently it's different particularly the collaterals so we see patients like this one that I showed you here who at six hours had TPA and had this clot dissolved and had a fantastic recovery from the stroke because this