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Image-guided surgery may reduce the re-excision rate in breast-conserving tumor-resection surgery, but
image guidance is difficult since the breast undergoes significant deformation during the procedure. In
addition, any imaging performed preoperatively is usually conducted in a very different presentation to that in
surgery. Biomechanical models combined with low-cost ultrasound imaging and laser range scanning may
provide an inexpensive way to provide intraoperative guidance information while also compensating for soft
tissue deformations that occur during breast-conserving surgery. One major cause of deformation occurs after
an incision into the tissue is made and the skin flap is pulled back with the use of retractors. Since the next
step in the surgery would be to start building a surgical plane around the tumor to remove cancerous tissue, in
an image-guidance environment, it would be necessary to have a model that corrects for the deformation
caused by the surgeon to properly guide the application of resection tools. In this preliminary study, two
anthropomorphic breast phantoms were made, and retractions were performed on both with improvised
retractors. One phantom underwent a deeper retraction that the other. A laser range scanner (LRS) was used to
monitor phantom tissue change before and after retraction. The surface data acquired with the LRS and
retractors were then used to drive the solution of a finite element model. The results indicate an encouraging
level of agreement between model predictions and data. The surface target error for the phantom with the
deep retraction was 2.2 +/- 1.2 mm (n=47 targets) with the average deformation of the surface targets at 4.2
+/- 1.6mm. For the phantom with the shallow retraction, the surface target error was 2.1 +/- 1.0 mm (n=70
targets) with the average deformation of the surface targets at 4.0 +/- 2.0 mm.
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