The first in-human clinical imaging of coronary arteries in vivo using a multimodality optical coherence tomography (OCT) and near-infrared autofluorescence (NIRAF) has been conducted successfully, and findings were published in JACC: Cardiovascular Imaging.
Researchers obtained OCT-NIRAF images (>50 mm pullback length) from 12 patients with coronary artery disease undergoing percutaneous coronary intervention (PCI). They developed a dual-modality intravascular imaging system and 2.6-F catheter capable of simultaneously acquiring OCT and NIRAF data from the same location on the artery wall.
While OCT provides a great level of morphologic detail, it has some limitations. Negative contrast features can muddle diagnoses, and key plaque features, such as lipids, may manifest as low OCT signal.
The OCT-NIRAF acquires synchronized OCT and NIRAF data at a rate of100 frames/second and the procedure is identical to current intravascular OCT—volumetric (3D) OCT-NIRAF data are acquired “by rotating and translating the driveshaft at a constant speed producing a helical scan.”
Between July 2014 and January 2015, patients undergoing PCI at Massachusetts General Hospital in Boston were enrolled in the study. First, researchers processed NIRAF emission intensity data by subtracting the image background. Then, they calibrated the NIRAF emission intensities based on the distance between the catheter and artery wall as determined by OCT. That way, the fluorescence signal could be quantitatively compared between patients.
Lesions were manually segmented using standard OCT image interpretation criteria in order to correlate the NIRAF emission intensities with different plaque features. Tissue type was categorized in the following manner: normal vessel wall, fibrotic, fibrocalcific, thick-cap fibroatheroma (ThCFA) if cap thickness >65 μm, thin-cap fibroatheroma (TCFA) if cap thickness ≤65 μ, and plaque rupture. An expert OCT image reader selected the plaques and was blinded to NIRAF data, to avoid bias.
Seventeen major coronary arteries were imaged, comprising 33 OCT-NIRAF pullbacks. Of these 17 coronary arteries, a high focal NIRAF signal was discovered in 5 arteries (29%), a low to moderate NIRAF signal in 4 (24%), and the rest (n=8; 47%) were NIRAF negative. Researchers noted a statistically significant difference of maximum NIRAF signal between plaque types (one-way ANOVA; P<.0001), but OCT-delineated TCFA and plaque rupture classes revealed much higher maximum NIRAF signal than the other plaques (P<.05). With the exception of fibrocalcific plaques and ThCFA (P=.65), all the other groups were statistically different from each other (P<.05).
An OCT-NIRAF dataset was obtained per patient (average length: 52 ± 10 mm) and the mean number of pullbacks per patient was 2.75 ± 1.23. The average amount of contrast administered to each patient was 44 ± 26 ml with a mean of 14 ± 2 ml per OCT-NIRAF pullback. No patient complications related to the imaging procedure were reported.
“By investigating the spatial relationship between NIRAF and arterial morphological features in vivo, we found that elevated NIRAF was associated with morphologic and/or mechanistic features of high plaque risk,” researchers wrote. “NIRAF was negative or low in plaques with a low-risk microstructural phenotype as determined by OCT (intimal hyperplasia, fibrous plaque, and fibrocalcific plaque).”
They added that the “focial spatial distribution of the NIRAF signal was a major unexpected finding of this study” and it “supports the potential additive nature of this imaging biomarker.”
Imaging technologies such as these will hopefully enable clinicians to better diagnose coronary plaque and predict patient risk for plaque progression.
Ughi GJ, Wang H, Gerbaud E, et al. Clinical characterization of coronary atherosclerosis with dual-modality OCT and near-infrared autofluoresence imaging. JACC Cardiovasc Imaging. 2016. doi:10.1016/j.jcmg.2015.11.020.