Diagnosis of Thin-Capped Fibroatheromas in Intravascular Optical Coherence Tomography Images

Abstract

Background Intravascular optical coherence tomography (IVOCT) images are recorded by detecting light backscattered within coronary arteries. We hypothesize that non- thin-capped fibroatheroma (TCFA) etiologies may scatter light to create the false appearance of IVOCT TCFA. Methods and Results Ten human cadaver hearts were imaged with IVOCT (N=14 coronary arteries). IVOCT and histologic TCFA images were co-registered and compared. Of 21 IVOCT TCFAs (fibrous cap <65 µm, lipid arc >1 quadrant), only 8 were true histologic TCFA. Foam cell infiltration was responsible for 70% of false IVOCT TCFA and caused both thick-capped fibroatheromas (ThCFAs) to appear as TCFA and the appearance of TCFAs when no lipid core was present. Other false IVOCT TCFA etiologies included SMC-rich fibrous tissue (12%) and loose connective tissue (9%). If the lipid arc >1 quadrant (“obtuse”) criterion was disregarded, 45 IVOCT TCFAs were identified, and sensitivity of IVOCT TCFA detection increased from 63% to 87%, and specificity remained high at 92%. Conclusions We demonstrate that IVOCT can exhibit 87% (95% CI 75% to 93%) sensitivity and 92% specificity (95% CI 86% to 96%) to detect all lipid arcs (both obtuse and “acute,” <1 quadrant) TCFA and we also propose new mechanisms involving light scattering that explain why other plaque components can masquerade as TCFA and cause low PPV of IVOCT for TCFA detection (47% for obtuse lipid arcs). Disregarding the lipid arc >1 quadrant requirement enhances the ability of IVOCT to detect TCFA.

Understanding Why and When Optical Coherence Tomography Does Not Detect Vulnerable Plaques

“…In a fourth study by Nakano et al, 5 the sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy of OCT were 77.8%, 97.4%, 60.9%, 98.8%, and 96.4%. In addition to being concordant with these studies, Phipps et al, 6 in this issue of Circulation: Cardiovascular…”

“…6 Other limitations to the accurate OCT assessment of lipid include artifacts caused by shallow or tangential beam angulation and drop-out and confounders such as the presence of fibrous cap microcalcifications or hemosiderin that can affect the appearance of lipid, cause difficulties distinguishing between lipid and calcium, and affect serial studies looking at pharmacological interventions, such as impact of statins on TCFA fibrous cap thickness. [7][8][9] (Of note, there is no difference between optical frequency domain imaging and frequency domain-OCT; they merely represent different implementations of the same fundamental technology.)…”

“…[7][8][9] (Of note, there is no difference between optical frequency domain imaging and frequency domain-OCT; they merely represent different implementations of the same fundamental technology.) Finally, the number of TCFAs in each of these studies was small [2][3][4][5][6] ; and there can be disagreement among pathologists as to whether specific lesions are or are not TCFAs.…”

“…More recently, it has been suggested that the use of 2 imaging technologies may improve on the diagnostic accuracy of any single technology and overcome limitations, such as the ones identified by Phipps et al 6 While once a fantasy, combined imaging devices are now a reality. However, when comparing different imaging modalities, there is rarely agreement among them about the diagnosis of individual TCFAs whether assessed in vivo or in vitro although agreement is generally worse in vivo adding to the issues about clinical vulnerable plaque detection.…”

“…Although Phipps et al 6 are to be commended on their study and although pathological correlations and understanding…”