Volumetric characterization of human coronary calcification by frequency-domain optical coherence tomography

Abstract

Background: Coronary artery calcification (CAC) presents unique challenges for percutaneous coronary intervention. Calcium appears as a signal-poor region with well-defined borders by frequency-domain optical coherence tomography (FD-OCT). The objective of this study was to demonstrate the accuracy of intravascular FD-OCT to determine the distribution of CAC.

Methods and results: Cadaveric coronary arteries were imaged using FD-OCT at 100-μm frame interval. Arteries were subsequently frozen, sectioned and imaged at 20-μm intervals using the Case Cryo-Imaging automated system(TM). Full volumetric co-registration between FD-OCT and cryo-imaging was performed. Calcium area, calcium-lumen distance (depth) and calcium angle were traced on every cross-section; volumetric quantification was performed offline. In total, 30 left anterior descending arteries were imaged: 13 vessels had a total of 55 plaques with calcification by cryo-imaging; FD-OCT identified 47 (85%) of these plaques. A total of 1,285 cryo-images were analyzed and compared with corresponding co-registered 257 FD-OCT images. Calcium distribution, represented by the mean depth and the mean calcium angle, was similar, with excellent correlation between FD-OCT and cryo-imaging respectively (mean depth: 0.25±0.09 vs. 0.26±0.12mm, P=0.742; R=0.90), (mean angle: 35.33±21.86° vs. 39.68±26.61°, P=0.207; R=0.90). Calcium volume was underestimated in large calcifications (3.11±2.14 vs. 4.58±3.39mm(3), P=0.001) in OCT vs. cryo respectively.

Conclusions: Intravascular FD-OCT can accurately characterize CAC distribution. OCT can quantify absolute calcium volume, but may underestimate calcium burden in large plaques with poorly defined abluminal borders.

Figure 1

Coronary artery calcification by FD-OCT and cryo-Imaging - Consecutive bright field (1^st row) and fluorescent (2^nd row) cryo-images visualized with the corresponding FD-OCT images (3^rd row) prior to quantification

Figure 2

Frame level measurement of plaque calcification - Corresponding bright field (A), fluorescent (B) and FD-OCT (C) images of coronary artery calcification with corresponding cryo (D) and FD-OCT (E) measurement tracings of calcium area, angle and depth at 1 degree circumferential intervals

Figure 3

Lipid masking human coronary artery calcification on FD-OCT - Bright field and fluorescent cryo images with corresponding OCT images showing 2 spotty calcifications (arrows in A, D and G) in the proximal coronary segment. Light attenuation caused by lipid is observed in FD-OCT images (arrowheads in H), which prevents visualization of corresponding calcification (arrowhead in B and E). Distal calcium in the same vessel is clearly visualized in both cryo and FD-OCT (arrows in C, F and I) images.

Figure 4

Correlations graphs (4A) and Bland-Altman plots (4B) between FD-OCT and cryo-imaging measurements of calcium-lumen distance, mean calcium angle and calcium volume – Correlation graphs and Bland-Altman plots for calcium-lumen distance (A), mean calcium angle (B), calcium volume for: the entire population (C), group A with fully visualized calcium borders (D) and group B with poor visualization of abluminal calcium border (E).

Figure 4

Correlations graphs (4A) and Bland-Altman plots (4B) between FD-OCT and cryo-imaging measurements of calcium-lumen distance, mean calcium angle and calcium volume – Correlation graphs and Bland-Altman plots for calcium-lumen distance (A), mean calcium angle (B), calcium volume for: the entire population (C), group A with fully visualized calcium borders (D) and group B with poor visualization of abluminal calcium border (E).

Figure 5

Three-dimensional reconstruction of coronary artery calcification - Bright field (A,D) and fluorescent (B,E) cryo-images visualized with the corresponding FD-OCT images (C,F). Coronary artery calcifications are seen within the arterial wall (arrows).