Objective To investigate the difference of morphology and blood flow of cavopulmonary anastomosis by MRI and that by ultrasonic cardiography (UCG) in patients with bidirectional Glenn shunt (BGS).Methods Phase-contrast MRI (PC-MRI) and contrast enhanced MRI (CE-MRI) were performed for superior vena cava ( SVC ) and inferior vena cava (IVC) in 22 patients with BGS on 3.0 T MR scanner.PC-MRI was used for measuring blood flow and CE-MRI for illustrating morphology.The width,peak flow velocity and gradient pressure of cavopulmonary anastomosis were calculated by using Report Card software.The similar data of UCG was collected.The parameters by MRI and that by UCG were compared statistically by t test and Pearson correlation.Results Based on the MRI data,the blood flow of SVC [ ( 1.002 ±0.208) L/min ] was significantly lower than that of IVC [ ( 1.794 ± 0.392 ) L/min ] ( t =- 15.148,P ＜0.01 ),while the regurgitation fraction of SVC [ (26.54 ± 12.82)％ ] was significantly higher than that ofIVC [ ( 17.44 ± 10.17)％ ] (t =11.060,P ＜0.01 ).The morphology displayed with MRI angiography couldnot be detected with UCG.The width of cavopulmonary anastomosis measured by MRI [ (12.46 ±3.43 ) mm ] was significantly higher than that of UCG[ ( 11.04 ± 2.63 ) mm] ( t =4.048,P ＜ 0.01 ),while the peak flow velocity of cavopulmonary anastomosis measured by MRI [ (47.77 ± 10.44) cm/s] was significantly lower than that of UCG [ (52.19 + 9.63) cm/s] ( t =- 2.237,P ＜ 0.05 ).No significant difference was found in gradient pressure of cavopulmonary anastomosis between the values by MRI [(0.95+0.42) mm Hg(1 mm Hg =0.133 kPa)] and that by UCG [(1.12+0.38)mm Hg] (t=2.010,P ＞ 0.05).The width,peak flow velocity and gradient pressure of cavopulmonary anastomosis by MRI were closely correlated with those by UCG (r =0.858,0.489,0.427,all P＜ 0.05 ).Conclusions A good correlation is found in the width,peak flow velocity,and gradient pressure of the cavopulmonary anastomosis obtained by 3.0 T MRI and UCG.MRI is more useful tool to display the width and abnormal morphology of cavopulmonary anastomosis than UCG.