A catheter-based near-infrared scanning spectroscopy system for imaging lipid-rich plaques in human coronary arteries in vivo

Abstract

Although heart disease remains the leading cause of death in the industrialized world, there is still no method, even under cardiac catheterization, to reliably identify those atherosclerotic lesions most likely to lead to heart attack and death. These lesions, which are often non-stenotic, are frequently comprised of a necrotic, lipid-rich core overlaid with a thin fibrous cap infiltrated with inflammatory cells. InfraReDx has developed a scanning, near-infrared, optical-fiberbased, spectroscopic cardiac catheter system capable of acquiring NIR reflectance spectra from coronary arteries through flowing blood under automated pullback and rotation in order to identify lipid-rich plaques (LRP). The scanning laser source and associated detection electronics produce a spectrum in 5 ms at a collection rate of 40 Hz, yielding thousands of spectra in a single pullback. The system console analyzes the spectral data with a chemometric model, producing a hyperspectral image (a Chemogram, see figure below) that identifies LRP encountered in the region interrogated by the system. We describe the system architecture and components, explain the experimental procedure by which the chemometric model was constructed from spectral data and histology-based reference information collected from autopsy hearts, and provide representative data from ongoing ex vivo and clinical studies.

Reliable in vivo intravascular imaging plaque characterization: A challenge unmet

“…The first validation study of NIRS, performed in 126 coronary artery segments from 51 autopsy hearts, showed that NIRS could detect with high accuracy (0.80; 95% CI: 0.76-0.85) lipid cores with circumferential extent >60 o located in the superficial plaque (cap thickness <450µm). 66 In this study, which resulted in the first Food and Drug Administration (FDA) diagnostic label claim for lipid core plaque, plaque composition from histology was correlated with the block chemogram in NIRS which displays the probability of the presence of lipid tissue in a 2mm block of the coronary artery. These data were re-analysed by Kang et al 67 who also performed IVUS imaging and focused on the efficacy of the two modalities in assessing the phenotype of the plaque.…”

“…A low sensitivity (30%) in this study was reported that was attributed to the limited efficacy of NIRS in detecting fibroatheromas with small necrotic cores, while the false positive NIRS estimations were related to the increased lipid component seen in lesions classified as pathological intimal thickening. Two more recent reports took advantage of the data collected in the study of Gardner et al 66 to examine the efficacy of NIRS in detecting plaque morphology: in the study of Puri et al 68 NIRS was able to detect fibroatheromas with a moderate accuracy (c-index: 0.71) while Inaba et al 69 examined the efficacy of this modality in detecting TCFA -which however were only 10 in this dataset -and showed that a maximum lipid core burden index in a 4mm segment≥323 was able to identify TCFA with an excellent accuracy (area under the curve, AUC: 0.84, Supplementary table 4).…”

“…The study of Gardner et al focused on the detection of large lipid cores, which apparently can be accurately detected by the modality while the study of Puri et al and Inaba et al that analysed the same dataset focused on the efficacy of the technology in detecting specific plaque phenotypes. 66,68,69 Histopathological studies can be challenging due to the tissue shrinkage, histology artefacts, movement of tissue between imaging and sectioning and the different types of flushing and fixation protocols used.…”

Lipid detection in atherosclerotic human coronaries by spectroscopic intravascular photoacoustic imaging

“…Near infrared reflection spectroscopy (NIRS) is an intravascular catheter-based technique that utilizes optical absorption to detect lipid-core lesions. It lacks depth resolution, however, and cannot locate the position of the lipid-core relative to the lumen boundary [13]. By combining NIRS with IVUS, morphological imaging is added to lipid detection, but the amount and the location of the lipid relative to the lumen remains unknown [14].…”