RESUMEN
Objective To establish the reference ranges of the spatial angles among cardiac chambers and great vessels in second and third trimester fetuses measured by spatiotemporal image correlation (STIC).Methods Volume images of 352 normal fetuses from 20 to 38 weeks of gestation were recruited in the study.An off-line analysis of acquired volume datasets was carried out with multiplanar mode.Parameters measured included angles between:(1) the 4-chamber view and the left ventricular long axis view; (2) the left ventricular long axis view and main pulmonary artery; and (3) the ductal arch and aortic arch.The relationships between above-mentioned angles and gestational age were assessed by correlation and regression analysis.Results The angle between the 4-chamber view and the left ventricular long axis view (range:55.7° - 35.7°,mean:45.7° ± 5.12°) was uncorrelated with gestational age (r = 0.03,P = 0.51).In contrast,the angle between the left ventricular long axis view and main pulmonary artery,and the angle between the ductal arch and aortic arch were correlated with gestational age (P ＜ 0.001),and the correlation coefficient was - 0.53 and 0.57 respectively.The best-fit exponential curve regression equations of the angle between the left ventricular long axis view and main pulmonary artery was:Y = 154- 4.24X +0.05X2 ,and the angle between the ductal arch and aortic arch was:Y = - 20.8 + 2.65X - 0.37X2.Conclusions The angles among cardiac chambers and great arteries of fetuses from 20 to 38 weeks of gestation can be quantitatively measured by STIC.The reference ranges provide a reliable quantitative standard to estimate the spatial relationships of the cardiac large arteries of fetuses,which may be clinically useful in prenatal screening congenital heart disease.