Two recently introduced intravascular ultrasound (IVUS)-derived, histology-validated technologies – Virtual Histology (VH) and Integrated Backscatter (IB) – classify atherosclerotic plaque components. However, there is little data comparing these two techniques, especially the impact of coronary artery calcium. Methods. We assessed 92 coronary arteries from 32 autopsied specimens. IVUS imaging was performed 50mm from the LMCA ostium; and using greyscale IVUS, we selected 29 segments(10 calcified segments vs 19 non-calcified segments) and compared mean % plaque components. Results. Pt age was 46짹8.9 yrs and 90% were males. The combination of fibrotic and fibrofatty plaque by VH-IVUS was larger than the combination of fibrotic and dense fibrotic plaque by IB-IVUS (78.51짹9.92% vs 63.31짹8.22%, p=0.01 in calcified lesion vs 92.65짹6.88% vs 71.93짹11.26%, p<.0001 in non-calcified lesion). Similarly, the lipidic plaque component of IB-IVUS was greater than the combination of fibrofatty and necrotic core plaque components by VH-IVUS (32.83짹9.18% vs 20.15짹3.75%, p=0.006 in calcified lesion vs 26.50짹11.36% vs 13.95짹6.03%, p<.0001 in non-calcified lesion). Most importantly, VH-IVUS detected more calcium than IB-IVUS (p=0.011, Table). Conclusion. Both VH-IVUS and IB-IVUS were developed to improve on the major limitation of greyscale IVUS, its inability to assess plaque composition. However, the above results show clear discrepancies between the two techniques. Resolving these discrepancies will require either histopathololgy or clinical validation through long-term follow-up studies.