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Schwarz SW, Mathias CJ, Sun JY, Dilley WG, Wells SA Jr, Martell AE, Welch MJ.Schwarz SW, et al.Int J Rad Appl Instrum B. 1991;18(5):477-81. doi: 10.1016/0883-2897(91)90108-w.Int J Rad Appl Instrum B. 1991.PMID: 1917517