Three-Dimensional Echocardiography: Technical Aspects And Methodology
The heart is an organ composed of complex anatomical structures and is in constant motion. Two-dimensional echocardiography can obtain partial information about the spatial and temporal relations between cardiac structures during the cardiac cycle, derived from the view of a theoretically infinite number of topographical sections. The analysis requires a difficult mental process of stereoscopic image reconstruction of the heart, resulting in a somewhat subjective assessment of the structures under consideration, and the need for geometric assumptions for calculation of structural and functional parameters.
To overcome these limitations scholars have tried for more than 30 years to develop techniques for the visualization of cardiac structures in three dimensions. In all these years, technology has provided the basis for writing a new and exciting chapter of ultrasonography: three-dimensional echocardiography (3DE). This revolutionary instrumental approach has several advantages over conventional techniques and the limitations of the method can certainly be overcome by further technological effort. There is no doubt that the advent of 3DE allows a more accurate, fast, easy and quantitative assessment of the anatomy of the heart, thereby reducing the subjectivity in the interpretation of images 1.
The key stages for a three-dimensional reconstruction of the images are: (1) acquisition of two-dimensional images with spatial and temporal information, (2) digitization of cross-sectional images sequentially sampled in order to allow for computer analysis, (3) reconstruction according to spatial-temporal sequences and visualization of structures in three dimensions. Data acquisition can be done with both, transthoracic and transesophageal probes. There are two basic techniques of acquisition: random, where the operator is not bound by a precise sequence of scans and can use different windows in a non fixed order, and sequential, which provides for scheduled scan images at regular intervals or angles, according to different approaches: linear or parallel, angular (fan-like) and rotational . In the past, with this type of approach, the probe was made to move through two computer-controlled mechanical supports.
In years past, the above acquisition technologies, which allowed a method of reconstruction off-line by using a complex computerized system for the sampled data sets, were used. In fact, once acquired, the two-dimensional sections are assembled and re-aligned in the correct sequence of space and time within the cardiac cycle by a process of data processing after acquisition. The result of this procedure is the average of data from several cardiac cycles with large interpolation of “voxels” (minimum volume element which is a three dimensional image), to avoid missing data, the intervals between the other two-dimensional section 3.
Currently three-dimensional echocardiography uses more advanced technology that delivers in real-time 3D volume of the region studied. This approach overcomes the limitations of off-line mode, with the possibility of an instant view of two orthogonal planes, allowing for greater efficiency and focusing the beam in 3D (voxel) spatial and temporal resolution while maintaining a high quality 4.
The transducer allows simultaneous acquisition and presentation of data in a region of interest in real time5. Obviously, this region of interest may not be broad enough to allow visualization of large structures, such as the left ventricle. This limitation is overcome by merging of datasets obtained from several neighboring cardiac cycles to create a larger dataset (“full volume mode “) 6.
Depending on the purpose of examination, different display modes can be used. One can choose to see sections of two-dimensional cross-sectional volumetric datasets obtained using any desired cutting plane (“anyplane” method), or coaxial cross sections (“OmniPlan” method), or a number of intersecting parallel sections (“paraplane” method)7.
The anatomical view can be created thanks to the techniques of rendering 3. A greater amount of morphological information can be extracted from the images displayed with volume-rendering techniques. These images represent the true morphology of the region of interest, displaying the cardiac structures in the same way as would be seen in vivo by the cardiac surgeon. Depending on the setting of the images (color, opacity and tone gradations) structures may appear solid or transparent, so that one gets information about the structures on diverse plans8. Moreover, the three-dimensional reconstructed images can be freely rotated or cut on computers, facilitating the viewing of the structures of interest from the most appropriate angles to obtain a complete and accurate analysis3.
References
1. Badano LP, Dall’Armellina E, Monaghan MJ, Pepi M, Baldi M, Cinelli M, Fioretti PM. Real-Time Three-Dimensional Echocardiography: Clinical Technological Gadgets or Tools? Journal of Cardiovascular madicine 2007.8.
2. Xie MX, Wang XF, Cheng TO, Lu Q, Yuan L, Liu X. Real-Time 3-Dimensional Echocardiography: a review of the Development of Technology and Its clinical application. Progress in Cardiovascular Disease 2005, 48:209-225.
3. Nucifora G, Baldi M, Badano LP, Gianfagna P Tosoratti And Part # Three-dimensional echocardiography. Detailed technical and application for evaluation of morphology and ventricular function. The Three-Dimensional Echocardiography in real time in routine echocardiography laboratory. Theoretical and practical course, Udine 2006.
4. Wang XF, Deng YB, Nanda NC, Deng J, Miller AP, Xie MX. Live three-dimensional echocardiography: Imaging Principles and clinical application. Echocardiography 2003; 20 (7) :593-604.
5. Sugeng L, Weinert L, Thiele K, Lang RM. Real-time three-dimensional echocardiogrphy matix using a novel array transducer. Echocardiography 2003; 20 (7) :623-35.
6. Pepi M, Tamborini G, Ponton G, et al. Initial experience with a new on-line transthoracic three dimensional technique: assessment of Feasibility and diagnostic potential. Ital Heart J 2003; 4 (8) :544-50
7. Salustri A, Kofflard MJ, Roelandt JR et al. Assessment of left ventricular outflow in hypertrophic cardiomyopathy using anyplane paraplane and analysis of three-dimensional echocardiography. Am J Cardiol 1996; 78 (4): 462-8
8. Roelandt JR. Threedimensional echocardiography: the future today! Acta Cardiol 1998; 53 (6) :323-36
Arcangelo D’Errico, Milena Sidiropulos, Luigi Ferrara, Pasquale Guarini
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