Intuitive modeling of right ventricular shape

A quantitative characterization of the shape of the right ventricle (RV) of the heart is needed for accurate modeling of the mechanics of the ventricle as well as for better measuring the volume of the ventricle from technologies such as 2D ultrasound, bi-planar ventriculography, and sonomicrometry. A technique was thus developed for modeling RV shape. First, a high-resolution MR image set was obtained of the freshly excised lamb heart under various passive pressurizations of both ventricles ranging from 5 to 30 cmH 2 O simulating end-diastole in the beating heart. Typically, 2-3 full images were obtained for each heart. Images were obtained with a multislice spin-echo T1-weighted sequence with the slice plane orientation early equal to the short-axis view of the heart. A 3D characterization of shape was obtained by first characterizing inter-slice changes in shape and orientation and then characterizing the shape of a single representative slice. The slice chosen to represent the RV was in the region directly below the tricuspid valve since it is both near to the apex-base center of the RV and has the greatest size. Intuitive deformations were applied to an initial circular arc anchored at the endpoints of the freewall and initially passing through a point near the center of the freewall contour, so as to best match the true freewall contour. These include a leaning of the circular arc parallel to the septal axis, a flattening perpendicular to the septal axis, a tucking-in or sharpening of the curvature near the junction with the septum, and a pinching- in at a point or points near its center towards the septum, all, in an attempt to account for the asymmetry and non- circularity deformed circular arc which effectively produces tow independent arcs. For all but one of the anterior and posterior arcs in 13 heart shapes, pinch-deformed arcs could be obtained whose average radial distance from the true RV chamber contour was less than 0.9 mm and averaged 0.5 mm for the anterior arc and 0.66 mm for the posterior arc. Worst- case deviation in parameters of the pinched-arc model of cross-sectional shape, and radii of curvature and the RV freewall-septum junction angle due to worst-case deviation in landmark location are 19 percent +/- 11 percent, 10 percent +/- 6 percent, 10 degrees +/- 4 degrees, and 12 degrees +/- 6 degrees. If landmark localization variability is minimized with a rigid translate offset scale model of the landmark region, average measurement error as determined in an adjacent slice comparison was 11 percent +/- 5 percent, -3 percent +/- 2 percent, 7 degrees +/- 2 degrees, and -7 degrees +/- 2 degrees.