The 'spin' technique: a new method for examination of the fetal outflow tracts using three-dimensional ultrasound.

BACKGROUND AND OBJECTIVE

The prenatal detection of congenital heart defects remains one of the most difficult challenges for the sonologist/sonographer when performing the second- or third-trimester screening examination. The four-chamber view has been used for a number of years as the primary screening image for detection of heart defects, but the inclusion of the right and left outflow tracts increases the detection of cardiac malformations. One of the difficulties, however, is obtaining and interpreting two-dimensional images of the outflow tracts. This paper reviews a new technique using three-dimensional (3D) multiplanar imaging that allows the examiner to identify the outflow tracts within a few minutes of acquiring the 3D volume dataset by rotating the volume dataset around the x- and y-axes.

METHODS

3D multiplanar imaging of the fetal heart using static 3D or spatio-temporal image correlation (STIC) imaging allows the examiner to obtain a volume of data that can be manipulated along the x- and y-axes using reference points from the four-chamber view, five-chamber view, three-vessel view at the level of the bifurcation of the pulmonary arteries, and three-vessel view at the level of the transverse aortic arch and trachea.

RESULTS

The full length of the main pulmonary artery, ductus arteriosus, aortic arch and superior vena cava could be identified easily in the normal fetus by rotating the volume dataset along the x- and y-axes. The vessels were identified using the four-chamber view, the five-chamber view, and the two three-vessel views. The technique was useful in identification of d-transposition of the great vessels and evaluation of the outflow tracts in hypoplastic left heart syndrome.

CONCLUSION

3D multiplanar evaluation of the fetal heart allows the examiner to identify the outflow tracts using a simple technique that requires only rotation around x- and y-axes from reference images obtained in a transverse sweep through the fetal chest.