Initial study of breast tissue retraction toward image guided breast surgery

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.