Contrast Transcranial Doppler Ultrasound in the Detection of Right-to-Left Shunts: Comparison of Echovist<sup>®</sup>-200 and Echovist<sup>®</sup>-300, Timing of the Valsalva Maneuver, and General Recommendations for the Performance of the TestDirk W. Droste, E. Bernd Ringelstein, Jörg Stypmann et al.|Cerebrovascular Diseases|2002Cited by 28