Three-dimensional Echocardiography: The Value of an Added Dimension
This review describes the utility of three-dimensional echocardiography in studying the cardiac anatomy and function of the left ventricle, mitral, aortic and prosthetic valves. It gives a new physiological and pathophysiological knowledge, accurate and precise assessment of the left ventricular size and function and improved characterization of valvular and structural disease.
Three-dimensional echocardiography (3D Echo) is an important imaging tool because of its ability to better understand relevant cardiac anatomy and function. With the creation of full matrix array transducers, 3D Echo can now capture more real-life images of the heart as compared with traditional two-dimensional (2D) imaging. The scanning beam performs azimuth steering along the Y-axis in a phased array manner and produces 2D sector images. The 2D sector image performs elevation steering along the Z axis and finally produces a pyramidal 3D data set (Figure 1).
3D Echo can be compared to the door to a room, which one can enter with the purpose of studying the walls and the structural content from whichever angle desired (Figure 2).
It gives a more advanced physiological and pathophysiological knowledge, far more accurate and precise assessment of left ventricle (LV) size and function, and improved characterization of valvular and structural disease, especially of the mitral and aortic valves. The specific application of 3D to the LV and aortic, mitral and prosthetic valves is discussed below.
The mitral valve has a complex arrangement and remains as one of the most challenging structures to image in 2D echocardiography. It has a saddle shape and a variety of scallops on both its leaflets and additional subvalvular apparatus that make it a complex three-dimensional structure, difficult to comprehend with 2D echo images alone. It takes several 2D echo images to conjure up a mental 3D image of the mitral valve. 3D echo takes away some of that guesswork and improves our understanding of the anatomy and pathology of the mitral valve (Figure 3).
While 3D Transoesophageal Echocardiography (3D TEE) is ideally suited for imaging the mitral valve, the aortic valve (AV) can also be imaged suitably by this means. The presence of thickened or calcified leaflets makes the valves more echodense, thereby enabling easier visualization by 3D TEE. Imaging the AV using live 3D imaging is useful during transcatheter aortic valve implantation, where the echodense prosthetic valve lends itself well to echo imaging (Figure 4).
The full volume mode is ideal for assessing left ventricular volumetrics. This requires manual definition of the septal, lateral, anterior, inferior and apical endocardial borders of the end-systolic and the end-diastolic frames, which is followed by an automated border-tracking algorithm. The system then calculates end-systolic as well as end-diastolic volumes by summation of volume pixels (‘voxels’) within pre-defined endocardial borders (Figure 5).
One of the principal advantages of 3D echocardiography is the improved ability to recognize the spatial arrangement of structures. Malfunctioning prosthetic valves, especially in the mitral position, can be imaged relatively easily and areas of malfunction identified. Lesions such as endocarditis, stuck leaflets, paravalvular leaks and ring dehiscence can not only be identified, but their exact location can be determined to provide the surgeon with more accurate information prior to surgical correction. Color 3D can also be used to identify paravalvular leaks and guide interventional therapy (Figure 6).
Although Real Time 3D Transoesophageal Echo (RT3DTEE) represents an important step, significant limitations remain. First, while 3D zoom and live 3D are indeed real-time modes, the acquisition of 3D full volume as well as 3D colour full volumes are based on automatic reconstruction from sub volumes and are therefore prone to artifacts from arrhythmias and ventilation, the so-called “stitch artifacts”. Second, as 3D echo obeys the same physical laws as 2D, poor 2D image quality will likely translate into similarly poor 3D image quality.[1,2]
The author gratefully acknowledges the help of Dr. Madhav Swaminathan and Duke University Medical Center, USA.
- Pandian NG, Nanda NC, Schwartz SL, et al. Three-dimensional and four-dimensional transoesophageal echocardiographic imaging of the heart and aorta in humans using a computed tomographic imaging probe. Echocardiography. Nov 1992; 9(6):677-687.
- Garcia-Orta R, Moreno E, Vidal M, et al. Three-dimensional versus two-dimensional transesophageal echocardiography in mitral valve repair. J Am Soc Echocardiogr. Jan 2007; 20(1):4-12.