Development of a semi-automated method for mitral valve modeling with medial axis representation using 3D ultrasound

Abstract

Purpose: Precise 3D modeling of the mitral valve has the potential to improve our understanding of valve morphology, particularly in the setting of mitral regurgitation (MR). Toward this goal, the authors have developed a user-initialized algorithm for reconstructing valve geometry from transesophageal 3D ultrasound (3D US) image data. Methods: Semi-automated image analysis was performed on transesophageal 3D US images obtained from 14 subjects with MR ranging from trace to severe. Image analysis of the mitral valve at midsystole had two stages: user-initialized segmentation and 3D deformable modeling with continuous medial representation (cm-rep). Semi-automated segmentation began with useridentification of valve location in 2D projection images generated from 3D US data. The mitral leaflets were then automatically segmented in 3D using the level set method. Second, a bileaflet deformable medial model was fitted to the binary valve segmentation by Bayesian optimization. The resulting cm-rep provided a visual reconstruction of the mitral valve, from which localized measurements of valve morphology were automatically derived. The features extracted from the fitted cm-rep included annular area, annular circumference, annular height, intercommissural width, septolateral length, total tenting volume, and percent anterior tenting volume. These measurements were compared to those obtained by expert manual tracing. Regurgitant orifice area (ROA) measurements were compared to qualitative assessments of MR severity. The accuracy of valve shape representation with cm-rep was evaluated in terms of the Dice overlap between the fitted cm-rep and its target segmentation. Results: The morphological features and anatomic ROA derived from semi-automated image analysis were consistent with manual tracing of 3D US image data and with qualitative assessments of MR severity made on clinical radiology. The fitted cm-reps accurately captured valve shape and demonstrated patient-specific differences in valve morphology among subjects with varying degrees of MR severity. Minimal variation in the Dice overlap and morphological measurements was observed when different cm-rep templates were used to initialize model fitting. Conclusions: This study demonstrates the use of deformable medial modeling for semi-automated 3D reconstruction of mitral valve geometry using transesophageal 3D US. The proposed algorithm provides a parametric geometrical representation of the mitral leaflets, which can be used to evaluate valve morphology in clinical ultrasound images.

Statistical Assessment of Normal Mitral Annular Geometry Using Automated Three-Dimensional Echocardiographic Analysis

“…The 3DE images of the mitral leaflets were semi-automatically delineated and geometrically modeled using previously described custom image analysis software [12]. First, the mitral leaflets were segmented with user-initialized 3D active contour evolution.…”

Automated Segmentation and Geometrical Modeling of the Tricuspid Aortic Valve in 3D Echocardiographic Images

“…Although the algorithm has not yet been tested on diseased subjects, the goal of the study is to demonstrate the feasibility of applying the method to a normal population before extending the methodology to pathological assessment. Given our previous success in using cm-rep to model both normal and diseased mitral valves [15] and the parallels between mitral and aortic valve disease processes, we expect the proposed method to characterize normal and pathological aortic cusp geometry equally well. The development of this automated technique is a step towards creating a practical, informative tool for preoperative assessment of patient-specific aortic valve morphology.…”

“…The manifold is discretely represented as a triangulated mesh, which can be sequentially Loop subdivided to a continuous limit. The medial template is generated using a method similar to that described in [15]. The 2D domain of the 3D medial mesh is homeomorphic to an annulus, in which the inner contour maps to the leaflet free edges and the outer contour maps to the semilunar attachments.…”

“…The Bayesian prior probability is modeled as a sum of validity constraints on medial geometry ( T validity , detailed in [15]), and a regularization component that acts on the model's two medial edges:…”

Computational Mitral Valve Evaluation and Potential Clinical Applications

“…More recently, MV modeling strategies have been transitioning to morphologically realistic patient-specific MV modeling utilizing real-time 3D imaging data. 70,92,93 The majority of the earlier computational models employed linear elastic material behavior of the valve structures. Recent modeling approaches have attempted to employ more realistic nonlinear hyperelastic anisotropic material properties for the MV apparatus components.…”