David A. Foley

Three- and Four-Dimensional Cardiovascular Ultrasound Imaging: A New Era for Echocardiography

Three-dimensional and four-dimensional ultrasonography were pioneered in the 1960s yet have been used little clinically. Only recently have advances in cardiovascular ultrasound equipment and in digital image storage, manipulation, and display techniques made three- and four-dimensional imaging clinically feasible. In this report, we review the historical development of these technologies during 3 decades to their culmination in current state-of-the-art technology. Examples of such multidimensional images are presented, with special emphasis on clinical applications. Although several limitations persist, three-dimensional cardiovascular ultrasonography seems likely to enhance imaging of the heart and vessels in a manner similar to the advent of two-dimensional echocardiography in the M-mode era. Clinician-scientists will soon be able to extract an object, such as the heart, from the body electronically for the purpose of anatomic, functional, and histologic analysis without adverse effect on the patient.

Three-dimentional ultrasound imaging of the atrial septum: Normal and pathologic anatomy☆

OBJECTIVES This study investigated the feasibility of producing three-dimensional gray scale ultrasound images of the atrial septum to demonstrate normal and pathologic anatomy. BACKGROUND Two-dimensional echocardiography is the principal technique used for imaging the atrial septum. Although the diagnostic accuracy of two-dimensional echocardiography is high, its capability for displaying complex three-dimensional relations is limited. METHODS Three-dimensional ultrasound images were reconstructed from tomographic images obtained during routine transesophageal echocardiographic examinations. Custom-made semi-automatic algorithms for image enhancement, interpolation and segmentation were used to produce volumetric gray scale images. Volume-rendered displays of the atrial septum were generated for analysis. Sequential three-dimensional images were generated through the cardiac cycle and displayed cinematographically to permit assessment of motion. RESULTS The three-dimensional images obtained from six patients clearly demonstrated normal and pathologic anatomy of the atrial septum, including atrial septal defects, atrial septal aneurysm and aortic valve ring abscess. The images could be manipulated electronically to demonstrate spatial relations and internal structural details. CONCLUSIONS Three-dimensional gray scale reconstruction of ultrasound images obtained by transesophageal echocardiography is feasible. These images clearly demonstrate anatomic details and spatial relations. The gray scale images may be interactively manipulated to optimize the clinicians visualization of the atrial septum and its associated pathologic conditions.

Cerebral Ischemic Events After Diagnosis of Mitral Valve Prolapse A Community-Based Study of Incidence and Predictive Factors

Background and Purpose— Association of mitral valve prolapse (MVP) with ischemic neurological events (INEs) is uncertain. Methods— In the community of Olmsted County (Minn), we identified all MVP diagnosed (1989 to 1998) in patients in sinus rhythm with no prior history of INE. We measured INE rates and compared them with expected rates in our community to define the excess risk of INE. Results— Among 777 eligible subjects (age, 49±20 years; 66% female; follow-up, 5.5±3.0 years), 30 patients had at least 1 INE during follow-up (at 10 years, 7±1%). Compared with expected INEs in the same community, subjects with MVP showed excess risk of lifetime INE (relative risk [RR], 2.2; 95% CI, 1.5 to 3.2;P <0.001) and during follow-up under purely medical management (RR, 1.8; 95% CI, 1.1 to 2.8;P =0.009). Independent determinants of INE were older age (RR, 1.08 per year; 95% CI, 1.04 to 1.11;P <0.001), mitral thickening (RR, 3.2; 95% CI, 1.4 to 7.4;P =0.008), atrial fibrillation (AFib) during follow-up (RR, 4.3; 95% CI, 1.9 to 10.0;P <0.001), and need for cardiac surgery (RR, 2.5; 95% CI, 1.1 to 5.8;P =0.03). INE 10-year rates were low in patients <50 years of age (0.4±0.4%, P =0.60 versus expected) but were excessive in patients >50 years of age (16±3%, P <0.001 versus expected) or with thickened leaflets (7±2%, P <0.001 versus expected). Predictors of follow-up AFib were age, mitral regurgitation, and left atrium diameter (all P <0.01). Conclusions— In the community, subjects with MVP display a lifetime excess rate of INE compared with expected. Clinical (older age) and echocardiographic (leaflets thickening) characteristics define patients with MVP at high risk for INE, and subsequent AFib or need for cardiac surgery, both related to the degree of mitral regurgitation, increase the risk of INE.

Three-Dimensional Reconstruction of Color Doppler Jets in the Human Heart

A computer algorithm has been developed for segmentation and three-dimensional (3D) reconstruction of Doppler color-flow images. The algorithm enables the user to select a range of velocities, represented by colors, for segmentation and subsequent 3D reconstruction. The reconstructed flows are assigned a color palette and merged with the volume-rendered gray-scale image to produce a 3D image containing both flow and anatomic information. The results demonstrate the application of the algorithm to regurgitant and shunt jets with complex spatial and velocity patterns. We conclude that 3D reconstruction of selected color spectra (e.g., velocities) of Doppler color flows and surrounding anatomy is feasible in the clinical setting.

Image Enhancement by Noncontrast Harmonic Echocardiography. Part I. Qualitative Assessment of Endocardial Visualization

OBJECTIVE To determine whether harmonic imaging--use of signals with frequencies twice that of the transmitted ultrasound to produce ultrasound images--can improve endocardial border definition in patients who have technically difficult echocardiograms. METHODS We studied 29 patients with technically difficult echocardiograms (nonvisualization of 2 or more endocardial segments in a 16-segment model). Apical long-axis, four-chamber, and two-chamber images were acquired during fundamental imaging (at 2.0 and 3.5 MHz) and second harmonic imaging (3.5-MHz receive mode) in random order. Images were digitally stored and subsequently reviewed blindly for endocardial segment score (0 = not visualized; 1 = adequate; or 2 = excellent) and overall ranking of image quality (1 [best] to 3 [worst]). RESULTS Mean endocardial segment score was significantly better (P < 0.0001) for harmonic imaging (1.02 +/- 0.36) than for either fundamental mode (0.49 +/- 0.21 and 0.57 +/- 0.27 for the 2.0- and 3.5-MHz images, respectively). The harmonic images were ranked as better (P < 0.0001) than those of either fundamental mode: harmonic mean rank was 1.07 in comparison with 2.67 and 2.26 for the 2.0- and 3.5-MHz fundamental images, respectively. CONCLUSION Noncontrast harmonic imaging appreciably enhances endocardial definition in patients with technically difficult echocardiographic studies and significantly improves overall image quality.

Usefulness of harmonic imaging for left ventricular opacification and endocardial border delineation by optison.

Harmonic and fundamental imaging techniques were directly compared in 20 patients undergoing intravenous contrast echocardiography for enhancement of left ventricular endocardial border definition. Harmonic imaging demonstrated significantly enhanced left ventricular endocardial border detection and improved the duration and intensity of a contrast effect despite a reduced dosing requirement.

Multidimensional Visualization in Echocardiography: An Introduction

X-ray films depict three-dimensional objects as shadows in a two-dimensional plane; thus, objects become superimposed. Computed tomography and other types of tomographic imaging, such as ultrasonography, acquire two-dimensional images of a material property within a thin slice. Sequential adjacent two-dimensional tomograms can be used to construct three-dimensional displays of objects. Visualization, a field of computer science, enables scientists to measure image attributes (extraction of features), identify features (classification), separate objects from one another (segmentation), and produce comprehensible, information-dense images from three-dimensional data sets (rendering). A three-dimensional rendering of the heart can be used to represent only one component of the heart, such as the atrial septum or the ventricular chamber, and can be shaded or colored to enhance comprehension. Three-dimensional images rendered sequentially over time result in a dynamic four-dimensional display. This report describes multidimensional visualization of objects and tissues and specifically discusses examples from echocardiography.

Harmonic imaging: echocardiographic enhanced contrast intensity and duration.

The intensity and duration of contrast effect within the left ventricular cavity after an intravenous bolus of Levovist Injection were observed with both harmonic and fundamental imaging in nine patients with known or suspected coronary artery disease. Contrast intensity was assessed by a qualitative grading system (0, none; 1, weak; 2, moderate; 3, good) and by videodensitometric analysis of pixel intensity. Duration of left ventricular contrast effect was determined by measuring time from the initial visual appearance of contrast agent to its disappearance. The mean increase in pixel intensity within the left ventricular cavity from precontrast to peak contrast was significantly greater for second harmonic than for fundamental imaging (25.5 vs 7.1; P < 0.012). The mean contrast intensity qualitative score with harmonic imaging was higher (2.6 ± 0.73 vs 1.2 ± 0.44; P < 0.01) and the duration of contrast effect was longer (242 ± 131 s vs 53 ± 33 s; P < 0.004). Second harmonic imaging significantly enhanced contrast intensity and prolonged visible duration of contrast effect after a peripheral venous injection of Levovist.

Stability of the Defibrillation Probability Curve with the Development of Ventricular Dysfunction in the Canine Rapid Paced Model

Most patients with implantable defibrillators have diminished cardiac function. Progressive heart failure might impair defibrillation efficacy, leading to interpreted device, failure. This study sought to determine the effect of ventricular dysfunction on defibrillation energy using a biphasic endocardial system. Eleven dogs were ventricularly paced at 225 pulses/min for 2 weeks to induce ventricular dysfunction, and five control dogs remained unpaced. Dose response defibrillation probability curves were generated for each animal at baseline, after 2 weeks (at which time the pacemakers were turned off in the paced group), and then 1 week later. The defibrillation thresholds, ED20, ED50, and ED80 (the 20%, 50%, and 80% effective defibrillation energies, respectively) were determined for each dog at each study. In the paced dogs, the mean ejection fraction fell from 55% to 25% after pacing (P < 0.0001), and rose to 46% after its discontinuation (P = 0.0002). The defibrillation threshold, ED20, ED50, and ED80 remained unchanged in both the control and paced groups for all three studies, even after adjustment for dog weight or left ventricular mass. Rapid pacing produced no change in left ventricular mass. It induced ventricular cavity dilatation and wall thinning, which had opposing effects on defibrillation energy requirements, resulting in no net change of the ED50 in heart failure. In conclusion, the defibrillation efficacy of a biphasic transvenous system is not changed by the development of heart failure using the rapid paced canine model.

Multidimensional ultrasonic visualization in cardiology

Multidimensional echocardiography includes three-dimensional (3-D) and four-dimensional (4-D) imaging of cardiovascular structures. Compound scanning (in vitro) and three scan techniques for transesophageal echocardiographic (TEE) imaging (in vivo) are used for acquisition of 3-D images of the heart and great vessels. A computer algorithm for 3-D reconstruction of ultrasound images reduces operator interaction to the selection of regions of interest and appropriate border threshold values. Data are processed by automatic reregistration, speckle reduction, and contrast enhancement routines to facilitate determination of a threshold value. Mathematical morphologic filtering is used to minimize noise and small artifacts along the edges of the object. In vitro experiments show excellent accuracy of volume measurements in reconstructed objects. Visual comparison of a reconstructed and electronically sectioned heart with the similarly cut anatomic specimen demonstrates high fidelity in depiction of anatomic structures.<<ETX>>