Fig. 1From: Right-to-left shunt and subclinical ischemic brain lesions in Chinese migraineurs: a multicentre MRI studyThe four-level RLS categorization based on the microbubbles count. a Grade 0 = Negative; b Grade I = 1 ≤ MBs ≤ 10; c Grade II = MBs > 10 and no curtain; d Grade III = curtain. Abbreviations: RLS (right-to-left shunt); MBs (microbubbles)Back to article page