Volumetric Ultrasound: A Novel Methodology for 3D Evaluation of Cardiovascular Structure and Function

Abstract

INTRODUCTIONThree-dimensional reconstructions (3DR) of the heart and great vessels are conventionally formed by scanning a single two-dimensional (2-D) plane, and then combining the data in this scan with data obtained from other scan planes taken at different levels. Missing data between planes are filled in by interpolation. Applications of such 3DR's from ultrasonic, radionuclide and magnetic resonance images have yielded promising results (1). 3DR's of the left ventricle have been obtained from cardiac ultrasonic and ultrafast computed tomographic images in our laboratory (2,3). We have also utilized the reconstructed geometries for analysis of mechanical defonnation of the ventricular chamber and quantitative assessment of wall motion abnonnalities in diseased states (4).Ultrafast computed tomography, magnetic resonance imaging and positron emission tomography are expensive, time and labor intensive, often require injection of contrast agents and cannot be obtained rapidly to allow image acquisition and evaluation throughout interventions such as exercise. On the other hand, ultrasound imaging is completely non-invasive, portable, and allows rapid data acquisition. With the advent of sophisticated computer workstations, it is now technologically possible to perform on-line reconstruction of the 3D geometry of the cardiac chambers from cross-sectional ultrasound images.Although traditional 3D echocardiography of the heart is an excellent technique for structural definition, there are drawbacks. Since the heart is moving during this procedure, the data collection is usually gated to the respiratory and cardiac cycles. These limitations result in extraordinarily long data collection and study times. In addition, quantitative assessment of cardiac function based on the 3D reconstructions require that the contours of the heart be traced. Due to large amounts of interpolation and operator-to-operator variability in performing the tracings the 3D reconstructions are often inaccurate.Approximately 5 years ago a new type of three dimensional reconstruction technique was generated for cardiac ultrasound. In this technique a mechanical ultrasound transducer was used either through the esophageal approach or across the chest wall. Using a mechanical transducer with images obtained at equally spaced intervals of 1 0 to 10 0 of rotation along a mechanically fixed axis cardiac images are obtained. This technique uses respiratory and ECG gating to obtain the images. Missing data are filled in using a gray scale algorithm and data is smoothed. Data is represented in a as pseudo 3D fonnat allowing slicing of the cardiac structures at any angle. Figures 1 to 3 identify images obtained using these 3D volumetric data sets (5-8).1582 VOLUMETRIC THREE-DIMENSIONAL ECHOCARDIOGRAPHYRecently the Duke University National Science FoundationlEngineering Research Center for Cardiovascular Technologies has reported the development of a true 3-D real-time volumetric ultrasound imaging system (9, 10, 11). The unit can produce a 3-D volume...