George D. Stetten

Assessment of Regional Wall Motion Abnormalities with Real-Time 3-Dimensional Echocardiography

Accurate characterization of regional wall motion abnormalities requires a thorough evaluation of the entire left ventricle (LV). Although 2-dimensional echocardiography is frequently used for this purpose, the inability of tomographic techniques to record the complete endocardial surface is a limitation. Three-dimensional echocardiography, with real-time volumetric imaging, has the potential to overcome this limitation by capturing the entire volume of the LV and displaying it in a cineloop mode. The purpose of this study was to assess the feasibility of using real-time 3-dimensional (RT3D) echocardiography to detect regional wall motion abnormalities in patients with abnormal LV function and to develop a scheme for the systematic evaluation of wall motion by using the 3-dimensional data set. Twenty-six patients with high-quality 2-dimensional echo images and at least 1 regional wall motion abnormality were examined with RT3D echocardiography. For 2-dimensional echocardiography, wall motion was analyzed with a 16-segment model and graded on a 4-point scale from normal (1) to dyskinetic (4), from which a wall motion score index was calculated. Individual segments were then grouped into regions (anterior, inferoposterior, lateral, and apical) and the number of regional wall motion abnormalities was determined. The RT3D echocardiogram was recorded as a volumetric, pyramid-shaped data set that contained the entire LV. Digital images, consisting of a single cardiac cycle cineloop, were analyzed off-line with a computerized display of the apical projection. Two intersecting orthogonal apical projections were simultaneously displayed in cineloop mode, each independently tilted to optimize orientation and endocardial definition. The 2 planes were then slowly rotated about the major axis to visualize the entire LV endocardium. Wall motion was then graded in 6 equally spaced views, separated by 30 degrees, yielding 36 segments per patient. A higher percentage of segments were visualized with 2-dimensional versus RT3D echocardiography (97% vs 83%, respectively, P <.001). With the use of the 2-dimensional echocardiographic results as the standard, RT3D echocardiography detected 55 (96%) of 57 regional wall motion abnormalities. Analysis of the RT3D echocardiograms resulted in 3 false-negative and 5 false-positive findings. The total number of regional wall motion abnormalities was correctly classified by RT3D echocardiography in 19 (73%) of 26 patients. RT3D echocardiography detected 11 of 13 anterior, 19 of 20 inferoposterior, 9 of 9 lateral, and 15 of 15 apical wall motion abnormalities. An excellent correlation was found between the 2 techniques for assessment of the regional wall motion score index (r = 0.89, P <.001). This initial clinical study demonstrates the feasibility and potential advantages of RT3D echocardiography for the assessment of regional LV function. Compared with 2-dimensional echocardiography, this new method permits recording of the entire LV in a single beat, allowing the extent and location of the regional wall motion abnormalities to be determined.

Real-time, three-dimensional echocardiography : Feasibility of dynamic right ventricular volume measurement with saline contrast

BACKGROUNDnThe asymmetry and complex shape of the right ventricle have made it difficult to determine right ventricular (RV) volume with 2-dimensional echocardiography. Three-dimensional cardiac imaging improves visualization of cardiac anatomy but is also complex and time consuming. A newly developed volumetric scanning system holds promise of obviating past limitations.nnnMETHODSnReal-time, transthoracic 3-dimensional echocardiographic images of the right ventricle were obtained with a high-speed volumetric ultrasound system that uses a 16:1 parallel processing schema from a 2.5 MHz matrix phased-array scanner to interrogate an entire pyramidal volume in real time. The instrumentation was used to measure RV volume in 8 excised canine hearts; dynamic real-time 3-dimensional images were also obtained from 14 normal subjects.nnnRESULTSnThree-dimensional images were obtained in vitro and in vivo during intravenous hand-agitated saline injection to determine RV volumes. The RV volumes by real-time 3-dimensional echocardiography are well correlated with those of drained in vitro (y = 1.26x - 9.92, r = 0.97, P <.0001, standard error of the estimate = 3.26 mL). For human subjects, the end-diastolic and end-systolic RV volumes were calculated by tracing serial cross-sectional, inclined C scans; functional data were validated by comparing the scans with conventional 2-dimensional echocardiographic indexes of left ventricular stroke volume.nnnCONCLUSIONSnThese data indicate that RV volume measurements of excised heart by real-time 3-dimensional echocardiography are accurate and that beat-to-beat RV quantitative measurement applying this imaging method is possible. The new application of real-time 3-dimensional echocardiography presents the opportunity to develop new descriptors of cardiac performance.

Real-time volumetric echocardiography: the technology and the possibilities.

The heart is a dynamic organ with complexities in its shape. As such, it places special demands on three‐dimensional techniques for reconstruction. Real‐time volumetric echocardiography, which is based on phased array and parallel processing principles to enhance line density within a scan volume, provides rapid image acquisition. We introduce the principle, potential clinical importance, current limitations, and future of volumetric imaging methods.

Medial-node models to identify and measure objects in real-time 3-D echocardiography

A method is proposed for the automatic, rapid, and stable identification and measurement of objects in three-dimensional (3-D) images. It is based on local shape properties derived statistically from populations of medial primitives sought throughout the image space. These shape properties are measured at medial locations within the object and include scale, orientation, endness, and medial dimensionality. Medial dimensionality is a local shape property differentiating sphere-like, cylinder-like, and slab like structures, with intermediate dimensionality also possible. Endness is a property found at the cap of a cylinder or the edge of a slab. In terms of an application, the cardiac left ventricle (LV) during systole is modeled as a large dark cylinder with an epical cap, terminated at the other end by a thin bright slab-like mitral valve (MV). Such a model, containing medial shape properties at just a few locations, along with the relative distances and orientations between these locations, is intuitive and robust and permits automated detection of the LV axis in vivo, using real-time 3-D (RT3D) echocardiography. The statistical nature of these shape properties allows their extraction, even in the presence of noise, and permits statistical geometric measurements without exact delineation of boundaries, as demonstrated in determining the volume of balloons in RT3D scans. The inherent high speed of the method is appropriate for real-time clinical use.

ACTIVE FOURIER CONTOUR APPLIED TO REAL TIME 3D ULTRASOUND OF THE HEART

We describe an active contour based on the elliptical Fourier series, and its application to matrix-array ultrasound. Matrix-array, or Real Time 3D (RT3D), ultrasound is a relatively new medical imaging modality that scans a 3D-volume electronically without physically moving the transducer, allowing for real-time continuous 3D imaging of the heart. With the goal of automatically tracking the heart wall, an active contour has been developed using the elliptical Fourier series to find perpendicular lines intersecting an initial contour. The neighborhood defined by these perpendiculars is mapped into a rectangular space, called a swath, whose vertical axis represents the inside-vs-outside dimension of the contour (perpendicular to the contour), and whose horizontal axis represents parametric distance along the contour (tangent to the contour). A dynamic programming technique is then used to find the optimum error function traversing the rectangle horizontally, and this error function is mapped back into image space to yield a new contour. The method does not iterate, but rather simultaneously searches for the optimum contour within a limited domain. Results are presented applying the technique to RT3D ultrasound images of in vivo hearts.

Automated Identification and Measurement of Objects via Populations of Medial Primitives, with Application to Real Time 3D Echocardiography

We suggest that Identification and measurement of objects in 3D images can be automatic, rapid and stable, based on the statistical properties of populations of medial primitives sought throughout the image space. These properties include scale, orientation, endness, and medial dimensionality. The property of medial dimensionality differentiates the sphere, the cylinder, and the slab, with intermediate dimensionality also possible. Endness results at the cap of a cylinder or the edge of a slab. The values of these medial properties at just a few locations provide an intuitive and robust model for complex shape. For example, the left ventricle during systole can be described as a large cylinder with an apical cap at one end, a slab-like mitral valve at the other (closed during systole), and appropriate interrelations among components in terms of their scale, orientation, and location. We demonstrate our method on simple geometric test objects, and show it capable of automatically identifying the left ventricle and measuring its volume in vivo using Real-Time 3D echocardiography.

Active contour based on the elliptical Fourier series, applied to matrix-array ultrasound of the heart

We describe an active contour based on the elliptical Fourier series, and its application to matrix-array ultrasound. Matrix-array ultrasound is a new medical imaging modality that scans a 3D-volume electronically without physically moving the transducer, allowing for real-time continuous 3D imaging of the heart. Unlike other 3D ultrasound modalities which physically move a linear array, matrix array ultrasound is rapid enough to capture an individual cardiac cycle, yielding a temporal resolution of 22 volumetric scans per second. With the goal of automatically tracking the heart wall, an active contour has been developed using the elliptical Fourier series to find perpendicular lines intersecting an initial contour. The neighborhood defined by these perpendiculars is mapped into a rectangular space, called the 1D swath, whose vertical axis represents the inside-vs.-outside dimension of the contour (along the perpendicular), and whose horizontal axis represents parametric distance along the contour (tangent to the contour). A dynamic programming technique is then used to find the optimum error function traversing the rectangle horizontally, and this error function is mapped back into image space to yield a new contour. The method does not iterate, but rather simultaneously searches for the optimum contour within a limited domain. Results are presented applying the technique to 3D ultrasound images of in vivo hearts.

Shape recognition with the flow integration transform

Abstract We present the Flow Integration Transform (FIT), a method for determining the presence of a preconceived shape in a gray-scale image. The expected shape serves as a filter for detecting potential targets. The FIT performs a line integral of the dot product of two vectors: (1) the “flow”, a vector equal to the gradient of the images intensity but rotated counterclockwise by 90°, and (2) the local tangent to the path of integration. The path of integration follows the contour of the expected target. The integration is performed starting at each point in the image, producing a two-dimensional transform whose pixel value corresponds to the relative presence of the expected shape at each location in the input image. The transform exhibits the appealing feature that information widely dispersed in the image becomes concentrated in a local area of the transform. Compared to traditional template matching using two-dimensional convulution, the correlation in the FIT is inherently one-dimensional, resulting in less computation. Furthermore, by constraining operations to addition, subtraction, and shift-by-one-pixel, implementation in high-speed hardware is greatly facilitated, with total computation times in the microsecond range achievable with present hardware technology.

Core Atoms and the Spectra of Scale

Our purpose is to characterize figures in medical images as a first step toward finding and measuring anatomical structures. FOr clinical use, we require complete automation and reasonably short computation times. We do not require that a sharp boundary be determined, only that the structure be identified and measurements taken of its size and shape. Our method involves the detection and linking of locations within an image that possess high medialness, i.e. locations that are equidistant from two opposing boundaries. The method produces populations of core atoms, each core atom consisting of a center point and the two associated boundary points. We can cluster core atoms by the proximity of their centers and by the similarity of their size. We generate statistical signatures of clusters to identify the underlying figure. In particular, we compute three spectra vs. scale for a cluster, including (1) magnitude: the number of core atoms, (2) eccentricity: their aggregate directional asymmetry, and (3) orientation: their aggregate direction. We illustrate the production of these spectra for various graphical test images, demonstrating translational, rotational, and scale invariance of the spectra, as well as specificity between targets. We observe the effects of image noise on the spectra and show how clustering reduces these effects. Early results suggest that the scale spectra of core atoms provide an efficient and robust method for identifying figures, suitable for practical application in medical image analysis.

Detection and quantification of true 3D motion components of the myocardium using 3D speckle tracking in volumetric ultrasound scans: simulations and initial experimental results

We present a new method for detecting and tracking tissue motion in 3D. The method is based on the concept of tracking speckle patterns in 3D using the sum absolute difference (SAD) technique. One potential application of this method is to study the 3D motion of various regions of interest in myocardial tissue using volumetric ultrasound scans of the heart. This could be of great value in assessing the viability of the myocardium. Simulations of 3D speckle patterns were obtained for the real-time ultrasound volumetric scanner developed at Duke University. Volumes of data were studied in pairs. Motion was simulated as whole voxel translations in 3D. A kernel volume was selected and a larger surrounding search volume was then defined. The kernel volume was compared to al possible matching sub- volumes in the search volume using the SAD technique. After the best match was found, the 3D components of motion were calculated by measuring the relative shift of the best match sub-volume from the location of the kernel volume the process was repeated until a 3D map of motion for the first frame was obtained. The performance of the proposed tracking method as a function of the SNR was the plotted for each direction. Experiments were performed to evaluate the performance of the method in vitro. A tissue mimicking materials was imaged using a 5MHz piston transducer translated in 2D to obtain multiple volumes with known shifts. The tracking method was applied and its performance with different shift values was evaluated. The calculated shift values highly matched the true shift values within a small jitter error.