Fifteen patients suffering from medication-resistant hand tremors experienced an average 67 percent decrease in shaking symptoms after undergoing a scalpel-free surgery that used high-intensity sound waves to burn away tissue in an area of the brain that helps regulate movement. Dr. W. Jeffrey Elias, a neurosurgeon at the University of Virginia, presented the one-year study results Monday at a meeting of the American Association of Neurological Surgeons being held in New Orleans.