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Figure 3 Calcific coronary plaques imaged in vivo by optical coherence tomography (OCT) (A, C) and intravascular ultrasound (IVUS) (B, D). (A) This OCT image shows a well delineated, heterogeneous, signal-poor region corresponding to a macrocalcification (A, arrow), also seen in the corresponding IVUS image (B, arrow). A signal-rich fibrous band (A, two arrowheads) overlying the calcification is easily identified in the OCT image but is obscured by a saturation artifact in the IVUS image. (C) A thin layer of circumferential calcification is seen in this OCT image (arrows) as a well-defined, heterogeneous, signal-poor region within the vessel wall. A side-branch (arrowhead) can be seen adjacent to the guidewire artifact (*). (D) The extent of the calcifications (arrows) and their relation to the surrounding fibrous components of the plaque are not as clearly seen in the corresponding IVUS image. The borders of the guidewire (*) artifact are marked by dotted lines in A, C. Tick marks, 1 mm.