Mitral annulus segmentation from four-dimensional ultrasound using a valve state predictor and constrained optical flow

Measurement of the shape and motion of the mitral valve annulus has proven useful in a number of applications, including pathology diagnosis and mitral valve modeling. Current methods to delineate the annulus from four-dimensional (4D) ultrasound, however, either require extensive overhead or user-interaction, become inaccurate as they accumulate tracking error, or they do not account for annular shape or motion. This paper presents a new 4D annulus segmentation method to account for these deficiencies. The method builds on a previously published three-dimensional (3D) annulus segmentation algorithm that accurately and robustly segments the mitral annulus in a frame with a closed valve. In the 4D method, a valve state predictor determines when the valve is closed. Subsequently, the 3D annulus segmentation algorithm finds the annulus in those frames. For frames with an open valve, a constrained optical flow algorithm is used to the track the annulus. The only inputs to the algorithm are the selection of one frame with a closed valve and one user-specified point near the valve, neither of which needs to be precise. The accuracy of the tracking method is shown by comparing the tracking results to manual segmentations made by a group of experts, where an average RMS difference of 1.67 ± 0.63 mm was found across 30 tracked frames.

3DMAS Method (3D Mitral Annulus Segmentation Method): Algorithm to segment the mitral valve annulus in a 3D ultrasound frame showing a closed mitral valve.CLKOF Method (Constrained Lucas and Kanade Optical Flow Method): Geometrically constrained optical flow method designed to robustly track the mitral valve annulus between noisy ultrasound volumes.Figure optionsDownload high-quality image (108 K)Download as PowerPoint slideHighlights
► 4D mitral annulus segmentation algorithm changes methods based on the valve state.
► Valve state is automatically determined from the 3D ultrasound images.
► Closed valve annuli are directly segmented, whereas open valve annuli are tracked.
► Tracking is done using a geometrically constrained optical flow algorithm.
► Annulus delineations are user-independent given reasonable user inputs.