The Role of Spatio-Temporal Imaging Correlation (Stic) in the Prenatal Diagnosis of Congenital Heart Defects

Abstract

INTRODUCTIONSpatio-temporal image correlation (STIC) is a feature of four-dimensional ultrasonography (4D US) that allows the acquisition of volume datasets akin to blocks of pathological specimens, where all the anatomical information is contained in the block and the information displayed depends on the level at which the block is cut. STIC has the additional advantages that these planes can be assessed in a virtual beating heart, and that rendering techniques can be used to gain additional insight into the structure and function of the fetal heart.With the use of STIC, volume datasets from fetal heart are acquired with a single automated sweep of the transducer, spatial and temporal information are combined to display images that can be extracted from volume datasets. Thus, standard planes for fetal echocardiography, including the four-chamber view, left and right outflow tracts can be obtained from the volume datasets at the time of the sonographic examination or afterwards and novel planes for fetal echocardiography can also be obtained. In addition to this anatomic information, functional information of the fetal heart can be obtained, including the direction of blood flow if the volume dataset was obtained with color Doppler or high definition (HD) power Doppler.Accumulating evidence indicates that 4D US facilitates examination of the fetal heart 1-12 . Thus, 4D fetal echocardiography has the potential to reduce the operator dependency of two-dimensional (2D) US. Prenatal diagnosis of Congenital Heart Diseases (CHDs) is challenging because of the complexity of the fetal heart and the expertise required in performing fetal echocardiography. In addition, fetal and maternal motion, maternal body mass index, gestational age, adequacy of the amniotic fluid volume and fetal position are important factors that can affect image quality. Prenatal diagnosis of CHDs is important because unrecognized CHDs may be associated with worse neonatal outcome. This paper reviews some technical aspects of 4D US, including volume acquisition and rendering, displays modalities in 4D US and summarizes the evidence evaluating the accuracy and reproducibility of 4D US in the prenatal diagnosis of CHDs. ACQUISITION OF VOLUME DATASETS WITH 4D US AND STIC Volume acquisition with mechanical transducersThis is performed with an automated sweep of the transducer, acquiring sequential frames at a rapid rate. Acquisition time ranges from 5 to 15 sec; the longer the acquisition time, the better the spatial resolution. During acquisition, on the basis of changes in the cardiac motion, the STIC algorithm detects the fetal heart rate and synchronizes 2D images. Frames acquired during the same phase in the cardiac cycle are merged into one volume dataset representing approximately 40 volumes. After analysis and rearrangement, the dynamic images are displayed on the screen in three planes that are orthogonal to each other 8 .The image quality contained in an STIC volume dataset can be improved by optimizing the settings before acquisition. This c...