During the last 2 months, your department has compared 94 in…
During the last 2 months, your department has compared 94 internal carotid arteries evaluated by carotid duplex with angiography. The results showed 50 vessels had a hemodynamically significant lesion by either method. 40 vessels had no lesion by either method. In 1 case, the noninvasive ultrasound was negative, but the angiogram showed a 70-99% diameter reduction. In 3 cases, the noninvasive studies were consistent with a >50% diameter reduction, but the invasive study was read as normal. What is the negative predictive value?