Methods for Modeling and Predicting Mechanical Deformations of the Breast During Interventional Procedures

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Azar, Fred S
Metaxas, Dimitris N
Miller, Reid T

When doing high field (1.5T) magnetic resonance breast imaging, the use of compression plate during imaging after a contrast-agent injection may critically change the enhancement characteristics of the tumor, making the tracking of its boundaries very difficult. A new method for clinical breast biopsy is presented based on a deformable finite element model of the breast. The geometry of the model is constructed from MR data, and its mechanical properties are based on a non-linear material model. This method allows imaging the breast without compression before the procedure, then compressing the breast and using the finite element model to predict the tumor’s position. The axial breast contours and the segmented slices are ported to a custom-written MR-image contour analysis program, which generates a finite element model (FEM) input file readable by a commercial FEM software. A deformable silicon gel phantom was built to study the movements of an inclusion inside a deformable environment. The hyperelastic properties of the phantom materials were evaluated on an Instron Model 1331 mechanical testing machine. The phantom was placed in a custom-built pressure device, where a pressure plate caused a 14% (9.8mm) compression. The phantom was imaged in a 1.5T magnet (axial and coronal), in the undeformed and deformed states. An FEM of the phantom was built using the custom-written software from the MR data, and another FEM of the phantom was built using a commercial pre-processor from the phantom’s directly measured dimensions. The displacements of the inclusion center and its boundaries were calculated, both from the experimental and FEM results. The calculated displacements from both models are within 0.5mm of each other, and agree within 1.0mm with the experimental results. This difference is within the imaging error.

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University of Pennsylvania Department of Computer and Information Science Technical Report No. MS-CIS-99-13.
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