Sub DeleteCap3Word()
With ActiveDocument.Range
  With .Find
    .ClearFormatting
    .Text = "<[A-Z]{3}>"
    .Replacement.Text = ""
    .Forward = True
    .Wrap = wdFindStop
    .Format = True
    .MatchWildcards = True
    .Execute
  End With
  Do While .Find.Found
    Select Case .Text
      Case "MRI", "USB", "PSA"
      Case Else: .Words.First.Delete
    End Select
    .Collapse wdCollapseEnd
    .Find.Execute
  Loop
End With
End Sub