Vascular surgeons plan most arterial bypass grafts on the basis of experience and intuition: only after surgery is there a way to tell whether an artery has been grafted to the place best suited to restore blood flow with minimal complications. But a group led by Charles Taylor, a Stanford University mechanical engineer who studies the human vascular system, is proving the power of an experimental software system that lets surgeons "sketch" several possibilities and preview the likely results before making a single incision.

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