Xiang-Ning Li

Three-dimensional echocardiographic assessment of annular shape changes in the normal and regurgitant mitral valve

OBJECTIVES To compare mitral annular shape and motion throughout the cardiac cycle in patients with normal hearts versus those with functional mitral regurgitation (FMR). BACKGROUND The causes of mitral regurgitation without valvular disease are unclear, but the condition is associated with changes in annular shape and dynamics. Three-dimensional (3D) imaging provides a more comprehensive view of annular structure and allows accurate reconstructions at high spatial and temporal resolution. METHODS Nine normal subjects and 8 patients with FMR undergoing surgery underwent rotationally scanned transesophageal echocardiography. At every video frame of 1 sinus beat, the mitral annulus was manually traced and reconstructed in 3D by Fourier series. Annular projected area, nonplanarity, eccentricity, perimeter length, and interpeak and intervalley spans were determined at 10 time points in systole and 10 points in diastole. RESULTS The mitral annulus in patients with FMR had a larger area, perimeter, and interpeak span than in normal subjects (P <.001 for all). At mid-systole in normal annuli, area and perimeter reach a minimum, nonplanarity is greatest, and projected shape is least circular. These cyclic variations were not significant in patients with FMR. Annular area change closely paralleled perimeter change in all patients (mean r = 0.96 +/- 0.07). CONCLUSIONS FMR is associated with annular dilation and reduced cyclic variation in annular shape and area. Normal mitral valve function may depend on normal annular 3D shape and dimensions as well as annular plasticity. These observations may have implications for design and selection of mitral annular prostheses.

System for quantitative three-dimensional echocardiography of the left ventricle based on a magnetic-field position and orientation sensing system

Accurate measurement of left-ventricular (LV) volume and function are important to monitor disease progression and assess prognosis in patients with heart disease. Existing methods of three-dimensional (3-D) imaging of the heart using ultrasound have shown the potential of this modality, but each suffers from inherent restrictions which limit its applicability to the full range of clinical situations. The authors have developed a technique for image acquisition using a magnetic-field system to track the 3-D echocardiographic imaging planes and 3-D image analysis software including the piecewise smooth subdivision method for surface reconstruction. The technique offers several advantages over existing methods of 3-D echocardiography. The results of validation using in vitro LVs show that the technique allows accurate measurement of LV volume and anatomically accurate 3-D reconstruction of LV shape and is, therefore, suitable for analysis of regional as well as global function.

Quantification of gastric emptying and duodenogastric reflux stroke volumes using three-dimensional guided digital color Doppler imaging

OBJECTIVE To develop a non-invasive method for evaluating gastric emptying and duodenogastric reflux stroke volumes using three-dimensional (3D) guided digital color Doppler imaging. METHODS The technique involved color Doppler digital images of transpyloric flow in which the 3D position and orientation of the images were known by using a magnetic location system. RESULTS In vitro, the system was found to slightly underestimate the reference flow (by average 8.8%). In vivo (five volunteers), stroke volume of gastric emptying episodes lasted on average only 0.69 s with a volume on average of 4.3 ml (range 1.1-7.4 ml), and duodenogastric reflux episodes on average 1.4 s with a volume of 8.3 ml (range 1.3-14.1 ml). CONCLUSION With the appropriate instrument settings, orientation determined color Doppler can be used for stroke volume quantification of gastric emptying and duodenogastric reflux episodes.

Volumetric reconstruction and visualization in three dimensional echocardiography: in vitro investigation

An object spinning scan method was applied to acquire high resolution in vitro ultrasound images for the purpose of studying volume interpolation and rendering. Three dimensional (3D) reconstructions were accomplished for nineteen excised porcine and canine hearts. The resulting 3D images clearly revealed the 3D features with a user developed weighted opacity based interactive volume rendering approach. The 3D calculated left ventricular volumes correlated well to those measured from water displacement (r=0.9548). This study not only provides superior reference data sets investigation of volumetric reconstruction visualization methodologies, the employed methods of reconstruction and visualization can also be adapted to in vivo transesophageal 3D imaging.

Dynamic flow quantitation with spatial orientation guided digital color Doppler imaging: In vitro validation and initial in vivo experience

The assumptions of geometric shape and uniform velocity profile prohibit the use of conventional Doppler methods for volume flow quantification with irregularly shaped nonvascular passages in space. A flow quantification method that integrates a three‐dimensional (3‐D) position and orientation sensing system with digital color Doppler imaging approach has been developed. Methods: The optimized ultrasound system settings were predetermined using a static, laminar flow model. The instantaneous flow rate was measured by the integration of the area‐velocity product with angle correction. Initial in vivo studies quantified gastric emptying on five healthy volunteers 10 min after ingestion of a 500‐ml meat soup, postprandially. Digital Doppler images were obtained continuously covering a transpyloric flow episode, immediately following the 3‐D scan of the passage. The flow direction was derived from 3‐D reconstruction using the centroids of two short‐axis views. Results: In vitro validation showed the Doppler f...

Three‐dimensional Doppler ultrasound: A tool for the 21st century

Three‐dimensional (3‐D) ultrasound now offers a method to overcome former limitations of two‐dimensional (2‐D) Doppler. Important 3‐D areas include the spatial delineation of the patency and pathways of blood vessels as well as the measurement of flow in them. In our laboratory a variety of 3‐D uses has been investigated: detection and mapping of coronary arteries (3‐D power Doppler, in vitro), mitral valve regurgitation (3‐D color Doppler, in vitro and in vivo), and gastric flow (3‐D color Doppler, in vivo). Several different 3‐D approaches have been applied and results will be presented. However, in the future, it is believed that direct flow measurement can be achieved. Flow is equal to the integral of the velocities normal to a surface that cuts through a flow field. An arc of constant radius in a 2‐D‐sector scanner will inscribe an arc of a spherical surface, if rotated around the origin of the sector (e.g., multiplane transesophageal echocardiogram). The pulsed Doppler signals along the circumference of the inscribed arc represent the velocities normal to that surface. Integration of these velocities should provide direct measurement of the flow field cutting this inscribed surface. Algorithms for testing this strategy are under development.