Accuracy of OCT, grayscale IVUS, and their combination for the diagnosis of coronary TCFA: an ex vivo validation study

Objectives: This study sought to assess the accuracy of optical coherence tomography (OCT), gray-scale intravascular ultrasound (IVUS), and their combination for detecting thin-cap fibroatheromas (TCFA).

Background: The extent to which the imaging characteristics of OCT and IVUS correlate with histologically defined TCFA is unknown.

Methods: IVUS and OCT examinations identified focal plaques in 165 coronary arteries from 60 autopsy hearts. A total of 685 pairs of images of OCT and IVUS were compared with histology. By OCT, a TCFA was defined as a signal-poor region with diffuse borders and cap thickness <65 μm. By IVUS, a TCFA was defined by the presence of echolucent zones and/or ultrasound attenuation in areas of positive remodeling. By histology, 12 of 685 focal plaques were classified as TCFAs.

Results: With histology as the gold standard, the sensitivity, specificity, positive predictive value, negative predictive value, and overall diagnostic accuracy for OCT-derived TCFA were 100%, 97%, 41%, 100%, and 98%, respectively. The corresponding numbers for IVUS-derived TCFA were 92%, 93%, 19%, 99%, and 93%, respectively. The histological findings underlying the false positive diagnoses of OCT for TCFA included large amounts of foam cell accumulation on the luminal surface, large amounts of microcalcifications at the surface, large amounts of hemosiderin accumulation, or organized thrombus. In contrast, histological causes of mischaracterization of TCFA by IVUS were mostly TCFA. When both OCT and IVUS criteria for TCFA were required to be met, the sensitivity, specificity, positive predictive value, negative predictive value, and overall diagnostic accuracy were 92%, 99%, 69%, 99%, and 99%, respectively.

Conclusions: In the present study, neither OCT nor IVUS were optimal to detect TCFA. The combined use of OCT and IVUS may improve TCFA detection accuracy.