Principles for 4D Auto LAQ
For volume computation, a semi-automated segmentation approach was
applied. At the annular level, a mark was inserted in the center of the
mitral valve (MV) to initiate the algorithm. Using an extended Kalman
filter that incorporates the LA motion model, geometry, and edge
detection techniques, the segmentation procedure determines the
deformation of the three-dimensional model. Using differences in the
lengths of several lines perpendicular to each anatomical direction,
strain was assessed. Using a triangular mesh, eight longitudinal lines,
each connecting two opposing LA base points, were used to calculate
longitudinal strain. Seven circumferential lines are uniformly
positioned between the LA base and LA apex in order to compute the
circumferential strain. The strain duration for each frame was then
determined using the formula s(t) = (L(t) L(tr))/L(tr) x 100 percent,
where L(t) is the line length at time t and tr is the end diastolic time
of the left ventricle. To determine the global strain, the strains of
all significant directional lines were averaged. [9, 12, 13]