Fibrous Cap Thickness by Optical Coherence Tomography In Vivo.

BACKGROUND Optical coherence tomography (OCT) imaging is considered to be the only imaging modality with sufficient resolution to measure fibrous cap thickness (FCT) in vivo. However, reproducibility of the measurements in vivo has been unsatisfactory. OBJECTIVES The authors aimed to investigate whether satisfactory reproducibility of FCT measurements by OCT in vivo can be achieved between independent observers. METHODS One hundred seventy OCT pullbacks were analyzed by 2 independent observers with intravascular imaging expertise in accordance with current guidelines to assess the interobserver variability of FCT measurement by intraclass correlation coefficient (ICC). The main sources of the variability were analyzed and incorporated in lesion assessment criteria. The same 170 OCT pullbacks were reanalyzed by the same observers using the developed criteria, and the interobserver reproducibility of the measurements was reassessed. On the basis of the developed criteria, a third independent observer interpreted all 170 OCT images. Assessment of the maximal lipid arc was also undertaken similarly before and after the development of interpretation criteria. RESULTS The original ICC of the FC thickness was 0.56 (95% confidence interval [CI]: 0.38 to 0.69). The poor definition of necrotic core facing border of FC and the neointimal presence of macrophages and calcification contributed to the high interobserver variability of FCT measurement. The ICC of FCT measurements by OCT in vivo was 0.88 (95% CI: 0.80 to 0.93) after we developed lesion assessment criteria. The ICC for the maximal lipid arc assessment before and after was 0.76 and 0.82 respectively. The third independent observer was extensively coached and returned the ICC of 0.82 (95% CI: 0.74 to 0.87) with observer 1 and 0.90 (95% CI: 0.86 to 0.94) with observer 2. CONCLUSIONS Careful consideration of OCT features mimicking fibroatheroma lesions and imaging artifacts contributed to significantly higher levels of interobserver agreement. Interobserver variation can be partially resolved by development of standard interpretation algorithms.