Tangential Signal Dropout Mimicking the Appearance of Lipid-rich Plaques and Macrophage Infiltration on Optical Frequency Domain Imaging.

BACKGROUND Tangential signal dropout (TSD), which occurs when the optical frequency domain imaging (OFDI) beam strikes the vessel wall under a glancing angle and travels almost parallel to the vessel wall, is the most important imaging artefact leading to the erroneous diagnosis of lipid-rich plaques. AIMS This study aimed to evaluate the OFDI artefact of TSD, which mimics the appearance of lipid-rich plaque and macrophage (Mo) infiltration. METHODS A total of 1,019 histological cross-sections from 23 autopsy hearts were matched with the corresponding OFDI images. Of these, 232 OFDI cross-sections that contained signal-poor regions with diffuse borders were classified as lipid-rich plaques. The angle θ was calculated between the OFDI beam that strikes the edge of the luminal surface of the low-intensity region and that which strikes the surface line of the low-intensity region. RESULTS On histological evaluation, 182 (78%) cross-sections were classified as histologically lipidic/Mo infiltration, while the remaining 50 (22%) cross-sections were classified as histologically non-lipidic/Mo infiltration. The angle θ was significantly smaller in the non-lipidic/Mo infiltration group than in the lipidic/Mo infiltration group (12±6° versus 37±14°, p<0.001). Receiver operating curve analysis revealed that the optimal cut-off value of the incident angle for predicting TSD was 23° with an area under the curve of 0.98. CONCLUSIONS When the OFDI imaging beam strikes the tissue at an angle θ<23°, TSD artefact could occur. To eliminate image misinterpretation, our findings suggest that the OFDI catheter geometry should be considered for the accurate diagnosis of lipid-rich plaques and Mo infiltration.