Cost-effectiveness of imaging compared with the prevalence of appendicitis. The pretest probability, a surrogate for diagnostic certainty, must be greater than 99.5% before diagnostic laparoscopy becomes the most effective strategy at a willingness to pay of $50,000 per quality of life-adjusted year.Fig. 1. Kastenberg. Cost-Effectiveness of MRI During Pregnancy. Obstet Gynecol 2013.