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Grading classification of right-to-left shunts in contrast transcranial Doppler ultrasonography; (A) Grade 0TCD = no microbubbles; (B) Grade ITCD = 1 to 10 microbubbles (arrow); (C) Grade IITCD = 10 to 30 microbubbles but no curtain (arrow); and (D) Grade IIITCD = curtain-like microbubbles (arrow).
