Which is the best quantitative method to analyse regional transmural perfusion gradient with real-time myocardial contrast echocardiography? - Perez-David, E; Garcia-Fernandez, MA; Ledesma-Carbayo, MJ; Silva, J; de Isla, LP; Santos, A; Antoranz, JC; Malpica, N; Rosas, R; Desco, M (Circulation, 2002)