3-D echocardiography: new developments and future prospects

Due to limitations in transthoracic and occasionally transesophageal 2-D echocardiography with respect to volumetric analysis and morphologic and functional assessment in patients with congenital malformations and valvular heart disease, additional diagnostic tools have been established. In parallel with the rapid evolution in computer technology, 3-D echocardiography has grown into a well-developed technique, such as volume-rendered 3-D reconstruction, capable of displaying dynamic morphology depicting depth of the structures, their attachment, and spatial relation to the surrounding tissue. Nevertheless, the complexity of data acquisition and data processing required for adequate dynamic 3-D echocardiographic imaging and volumetric analysis does not allow to use this approach routinely. The commonly used dynamic 3-D echocardiography means off-line computer-assisted image reconstruction from a series of cross-sectional echocardiographic images using currently available transesophageal and transthoracic transducers. Alternatively, real-time 3-D echocardiography based on novel matrix, phased-array transducer technology has been introduced. Although this technique can be easily combined with any routine examination, its clinical use is limited because of a lower image quality in comparison with dynamic 3-D echocardiography. Up to now, there is no transesophageal approach available using real-time 3-D echocardiography. Recently, dynamic 3-D echocardiographic technique has matured noticeably. Beside the well-known sequential scanning, which is characterized by a fixed probe and patient in space and predetermined motion of the transducer, the freehand scanning using an electromagnetic location system has found its way to clinical environment. The main advantage of this technique is that the transducer can be freely moved by the examiner and, thus, the data set acquired within a routine examination. Also 3-D rendering and display have been developed further. In this respect, especially the "real-time rendering mode" allowing the reconstructed 3-D image to be animated and moved in space and to look at it from different perspectives has gained increasing acceptance. In valvular heart disease, reconstructive surgical treatment is aspired. 3-D echocardiographic imaging is the only technique providing "surgical views" prior to opening the heart. It is capable of distinguishing particular destructive substructures of the valves and the valvular apparatus. Especially in mitral valvular reconstruction, it is of clinical importance to achieve optimal surgical results. With respect to volumetric and mass analysis, 3-D echocardiography is more accurate and reproducible in comparison with conventional 2-D analysis. It provides data independent of geometric assumptions, what may considerably influence the results in the presence of wall motion abnormalities, especially in aneurysmatic ventricles. Volumetric analysis of the aneurysmal portion may also be helpful prior to surgical resection. 3-D echocardiography can also be recommended as a valuable additional approach to atrial septal defect (ASD), corrected transposition of the great arteries, cor triatriatum, and, within limits, to ventricular septal defect (VSD) as well. Especially with respect to ASD and VSD, the potential significance of 3-D echocardiography prior to device closure is emphasized. At present, its additional information in decision-making and the increasing number of clinical cases that can be addressed and answered already justify the clinical use of this technique.