Impersonate user SystemAdmin Sharepoint Programmatically

Dim tempsite As SPSite = New SPSite("http://localhost/a")
Dim usertoken As SPUserToken = tempsite.SystemAccount.UserToken()

Using site As SPSite = New SPSite("http://localhost/a", usertoken)
Using oWebsite As SPWeb = site.OpenWeb()

'bla bla bla your code inside here