In vivo finite element model-based image analysis of pacemaker lead mechanics

Background: Fractures of implanted pacemaker leads are currently identified by inspecting radiographic images without making full use of a priori know n material and structural information. Moreover, lead designers are unable to incorporate clinical image data into analyses of lead mechanics. Methods : A novel finite element/active contour method was developed to quantify th e in vivo mechanics of implanted leads by estimating the distributions of s tress, strain, and traction using biplane videoradiographic images. The non linear equilibrium equations governing a thin elastic beam undergoing 3-D l arge rotation were solved using one-dimensional isoparametric finite elemen ts. External forces based on local image greyscale values were computed fro m each pair of images using a perspective transformation governing the rela tionship between the image planes. Results: Cantilever beam forward solutio n results were within 0.2% of the analytic solution for a wide range of app lied loads. The finite element/active contour model was able to reproduce t he principal curvatures of a synthetic helix within 3% of the analytic solu tion and estimates of the helix's geometric torsion were within 20% of the analytic solution. Applying the method to biplane videoradiographic images of a lead acutely implanted in an anesthetized dog resulted in expected var iations in curvature and bending stress between compliant and rigid segment s of the lead. Conclusions: By incorporating knowledge about lead geometric and material properties, the 3-D finite element/active contour method regu larizes the image reconstruction problem and allows for more quantitative a nd automatic assessment of implanted lead mechanics. (C) 2001 Elsevier Scie nce B.V. All rights reserved.