Feinstein SB, Cheirif J, Ten Cate FJ, Silverman PR, Heidenreich PA, Dick C, Desir RM, Armstrong WF, Quinones MA, Shah PM. Safety and efficacy of a new transpulmonary ultrasound contrast agent: initial multicenter clinical results. J Am Coll Cardiol. 1990 Aug; 16(2):316-24.