Contrast ECHO using agitated saline is used to diagnose:

Contrast enhanced echocardiography is the preferred screening test for HPS. It uses agitated saline or indocyanine green to produce microbubbles at least 15 mm in diameter that are then injected intravenously. Under normal circumstances, these microbubbles are trapped in the pulmonary microvasculature and then absorbed. In patients with intracardiac or intrapulmonary shunting, microbubbles are seen in the left hea. Differentiation between intracardiac and intrapulmonary shunting is based on the timing of when these bubbles are found in the left hea. In intracardiac right-to-left shunts, these bubbles appear in the left hea in 3 heabeats after they appear in the right hea. In intrapulmonary shunts, these bubbles appear in 4-6 heabeats. Ref: Recent Advances in Hepatopulmonary Syndrome ; Ying-Wen, Page - 2