Expecting a mean plaque volume of 160±50 mm3 in a population of patients with ACS undergoing PCI, a sample size of at least 45 patients (52 lesions) with a recent (<15 days, but after 24 hours) STEMI or a non-ST elevation (NSTE)-ACS within 72 hours of symptoms would provide a 90% power to detect a 20% reduction in the plaque volume after TA with an alpha (probability value) of 0.05.