Background: iMAP is a new intravascular ultrasound (IVUS) derived technique for tissue characterization using spectral analysis. Since there is a need for reproducibility data to design longitudinal studies, we sought to assess the in vivo reproducibility of this imaging technique. Methods: iMAP (40 MHz, Boston Scientific Corporation) was performed in patients referred for elective percutaneous intervention and in whom a nonintervened vessel was judged suitable for a safe IVUS analysis. Overall 20 patients with 20 non-angiographically significant lesions were assessed by two independent observers. Five of these 20 patients received an additional iMAP analysis using a new IVUS catheter and using the same catheter after its engagement and reengagement. Results: The interobserver relative difference in plaque area was 2.5%. Limits of agreement for lumen, vessel, and plaque area measurements were 1.62, -2.47 mm(2); 2.09, -3.71 mm(2); 2.80, -3.72 mm(2); respectively. Limits of agreement for fibrotic, lipidic, necrotic, and calcified measurements were 1.32, -1.44 mm(2); 0.24, -0.36 mm(2); 1.50, -2.26 mm(2); 0.09, -0.11 mm(2); respectively. The intercatheter and intracatheter relative difference in plaque area were 0.9% and 4.1%, respectively. Although the variability for compositional measurements increased using two different catheters or using the same catheter twice, the variability for compositional measurements keeps always below 10%. Conclusions: Our analysis demonstrates that the geometrical and compositional iMAP analysis is acceptably reproducible. (c) 2011 Wiley Periodicals, Inc.