Echocardiography is the most widely used noninvasive cardiac diagnostic imaging modality. Recent technological advances have resulted in the development of sophisticated new tools that further refine the ability of echocardiography as a diagnostic modality as well as a guiding tool for various interventions. Of these novel technological advances, the most notable ones include 3D echocardiography, speckle-tracking echocardiography (STE), and intracardiac echocardiography (ICE).

This review describes the technological advances that resulted in the development of these modalities and the implementation of these modalities into clinical use.

3D echocardiography has evolved over the past decade from cumbersome reconstruction of multiple 2D images to real-time volumetric imaging.1 This revolutionary approach allows real-time 3D visualization of the heart, which has greatly impacted cardiac care.

The key difference between 3D and 2D echocardiography is the volumetric approach to data acquisition, visualization, and quantification. Volumetric imaging can be performed by three different approaches: freehand, mechanical, and electronic. In addition to advances in the electronic approach to 3D imaging, advances in transducer technology made the evolution in 3D technology possible. Until recently, 3D acquisition was done using sector phased-array and sparse 2D array. Sector phased-array added multiple 2D data sets together to create a reconstructed image. This technique was temporally limited by cardiac motion, and the image acquisition took up to 1 minute. Sparse 2D arrays rely on receiving data from different points at the same time. This is referred to as parallel processing. Sparse 2D arrays eliminated motion artifacts with higher frame rates. This technology requires the use of a small number of piezoelectric elements, which limit its use in difficult-to-image patients. Poor image quality and lack of practicality of these modalities limited 3D echocardiography from gaining widespread acceptance.2 The xMATRIX transducer (Philips Medical Systems, Andover, Mass) made real-time 3D imaging (Live 3D) possible. This transducer uses fully sampled 2D array technology. Roughly 3,000 piezoelectric elements are connected to integrated circuits within the transducer head. Traditional 2D images use digital signal processing, which is not practical with 3,000 elements, therefore, a hybrid technology was developed, using digital and analog processing to combat this problem. Image acquisition is done in two stages. In the first stage, signals are processed using low power analog circuitry. Digital beam-forming is then used to process and integrate the analog images.

3D Applications

Figure 1. Volume time curves generated using volumetric real-time 3D echocardiography for analysis of segmental left ventricular systolic function. Click on image for larger view

3D echocardiography is gaining widespread clinical use in the areas of real-time quantification of chamber volumes, analysis of global and regional left ventricular (LV) systolic function, evaluation of congenital anomalies, and assessment of valvular anatomy and function for surgical planning and after repair.3 One of the most common applications of echocardiography is assessment of LV systolic function. When 2D echo is used for this indication, geometric assumptions regarding the shape of the ventricle need to be made, limiting the utility of this modality for accurate assessment, which is critical for patient management. 3D echocardiography is able to quantify both left and right ventricular chambers with significantly more precision than 2D echocardiography3 (see Figure 1, at right). Recently, Sugeng et al compared real-time 3D echocardiography and cardiac CT with the standard reference technique of cardiac MR for the evaluation of left ventricular size and function. They found that LV volumes obtained from both cardiac CT and 3D echocardiography correlated strongly with values obtained by cardiac MR.4 3D echocardiography can provide information that conventional 2D echocardiography cannot yield, and does so more economically than cardiac CT or cardiac MR.

Currently, 3D echocardiography for valvular evaluation is used mainly for the evaluation of mitral valve structure. Given the unique hyperbolic, paraboloid geometric configuration of the mitral valve, its accurate assessment is optimized with 3D echocardiography, which gives a more realistic view of the complex saddle-shaped apparatus of the mitral valve. 3D echo can be used therefore for the evaluation of mitral valve stenosis, prolapse, and regurgitation.5

3D echocardiography also has significant implications for the repair of cardiac structural abnormalities, such as ventricular septal defect (VSD) closure.6 3D echocardiography was demonstrated to be more accurate than 2D transesophageal echocardiography (TEE) in measuring VSD size,7 and may lead to successful percutaneous procedures, reducing the need for open heart procedures.

STE: A Novel Technique

STE is a novel method for the quantification of myocardial strain. Speckle tracking is based on the concept that echocardiographic images of myocardium reveal acoustic markers where ultrasonic energy is created and destroyed based on the structure of the myocardium. These images create a “fingerprint” of the myocardium. Distances are measured between speckle points and plotted against the cardiac cycle. These measurements yield strain rates and velocities that can be synthesized and used to calculate myocardial dysfunction at specific locations.8,9

Figure 2. Vector velocity imaging (left) and the quantitative analysis based on it (right). Click on image for larger view

The greatest advantage of using speckle over tissue Doppler, the more commonly used method for obtaining tissue velocities and strain, is that speckle does not confine to the rules and limitations of Doppler, such as the Niquist limit, and the need to completely align the segment being evaluated with the echo beam. By using speckle, tissue velocities can be obtained of segments that are at various angles to the ultrasound beam, allowing for more accurate assessment of radial and circumferential strains in addition to longitudinal strain, thereby permitting more accurate assessment of LV mechanics. One approach for obtaining speckle tracking is by using velocity vector imaging (VVI, Sequoia, Siemens Medical Solutions Inc, Mountain View, Calif). VVI is a unique technique that uses a tracking algorithm for assessing myocardial velocities. These velocities are displayed as vectors overlaid into the 2D (B mode) image (see Figure 2, above). The length of the vector indicates the magnitude of the tissue velocity, and the direction of the vector indicates the direction in which the tissue is moving. The speckle-tracking algorithm of VVI is complicated and uses reference points including the mitral annulus, motion of the tissue/cavity border, motion of the tissue near the border, and periodicity of the heart motion of the R-R intervals.10 Although the signal processing is complex, the user interface is straightforward and requires only a single frame tracing of the endocardial border to extract quantitative time-motion data.11 This approach allows measurement of myocardial velocity and deformation (strain) in both apical and short axis views of the left ventricle, as well as assessment of LV torsion and can be implemented in more accurate evaluation of LV systolic and diastolic function, as well as in assessing for the presence of dyssynchrony. Some of the limitations of VVI include the fact that analysis of peak velocities includes postsystolic events that affect sensitivity and specificity with tissue Doppler, and translational motion that also affects VVI velocity data. In addition, like all quantitative echocardiographic methods, VVI requires adequate image quality.

Helle-Valle et al suggest that LV torsion is an important factor when considering left-sided filling and ejection fraction. They suggest that STE is an alternative to magnetic resonance imaging in the measurement of LV torsion. The authors offer that STE is an accurate, inexpensive, and simpler way to measure LV torsion as a novel method for LV function quantification.12 Thomas and Popovic had similar results confirming the accuracy of LV torsion via STE compared with cardiac MRI. They showed STE concordance of LV torsion values with tagged MRI and offer STE as a method of evaluating LV function that is more widely accessible.13

ICE: Gaining Traction

ICE is another exciting imaging modality that is gaining widespread acceptance and use. ICE is being used to guide a variety of percutaneous interventions including atrial septal defect and patent foramen ovale closures, balloon valvuloplasty, transseptal puncture, arrhythmia ablation, and cardiac biopsy. Direct visualization of cardiac structures prior to intervention is proving to be an extremely useful tool in minimizing complications and maximizing the efficacy of intervention. In addition, ICE can be used whenever a transesophageal echocardiogram is needed but is contraindicated, or in situations in which the information obtained by TEE is insufficient.14

The biggest challenge that ICE faced during its evolution was image quality. Penetration was limited, and it did not provide effective Doppler imaging. With the introduction of phased-array technology, deeper penetration and a wider spectrum of views became feasible. Compared with previous ICE catheters, which were single piezoelectric elements with mechanical rotation, phased-array catheters (AcuNav, Biosense, Webster, Calif) offer significant improvements in cardiac structure visualization. In one of the first safety and efficacy trials performed using this specific catheter,15 it was demonstrated that by placing the catheter at or slightly above the junction of the superior vena cava and right atrium, right and left heart structures were effectively imaged.

Figure 3. Image of the interatrial septum obtained using ICE. Arrow is pointing to a patent foramen ovale (PFO). RA is right atrium, LA is left atrium. Click on image for larger view

ICE is particularly important in identifying structures that are in proximity to a specific intervention that is being performed as well as identifying immediate complications. During transseptal puncture for percutaneous intervention, ICE can directly aid in the visualization of the interatrial septum (IAS). Visualizing the needle and the adjacent structures such as the aortic root can guide the operator in order to minimize complications. ICE can be used in the electrophysiology laboratory, when ablation catheter position is of crucial importance. Ablation of atrial fibrillation requires the crossing of the IAS. After this is performed and ablation occurs, ICE can illustrate the location, the size, and any complications of the tissue injury.16 Optimizing the size and location of the injury directly with ICE will potentially lead to more successful and lasting therapy. Recently, a smaller diameter catheter was released (8F vs 10F), which is also approved for imaging from within the left cardiac chambers. This technological advancement may expand the use of this technology to smaller adults and children, and could possibly result in fewer vascular complications.

The technologic advances in cardiac imaging have dramatically changed the way in which patients are diagnosed and treated. Since its infancy, echocardiography has dramatically impacted the delivery of cardiac care. There is mounting evidence that the recent developments in ultrasound imaging improve safety and efficacy of modern treatment modalities. With recent developments in the field, echocardiography remains a vital and readily accessible resource in the treatment and diagnosis of a variety of cardiac conditions.

Amit Mittal, MD, is a fellow; and Smadar Kort, MD, FACC, FASE, is director of cardiovascular imaging, director of echocardiography, and assistant professor of medicine, Health Sciences Center, Division of Cardiology, Stony Brook University Medical Center, Stony Brook, NY. For more information, contact .


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