Supplemental Materials
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Supplemental Figure 1. Partitioning analysis for IB-IVUS for IB-IVUS-derived TCFA
based on histologic identification of TCFA.
We sought to define TCFA based on IB-IVUS measurements by recursive partitioning analysis
(RPA) which is an exploratory multivariate method known as classification tree, allowing
identification of candidate variables in distinguishing subgroups, free of distributional and
linearity assumption. Among 360 plaques (18 TCFA and 342 non-TCFA on histology), RPA
firstly split the groups by % lipid area with a threshold of 32.3%, with the subgroup <32.3% lipid
area having no TCFA. Secondly, RPA split the subgroup >32.3% lipid area into two with a
threshold of 65.1% lipid area, with the subgroup >65.1% lipid area consisting of 3 TCFA and 0
non-TCFA. Then, RPA chose a threshold of 10.5mm2 in plaque area to best separate the
subgroup of % lipid area >32.3 but <65.1%. Subsequently, RPA chose a threshold of 72% in
plaque burden as the parameter to separate the subgroup with plaque area >10.5%. However, we
did not adopt this third parameter because of the limited number of TCFA (18) in our cohort.
Utilizing 2 variables derived from the exploratory analysis shown as above, finally we defined
IB-IVUS-derived TCFA as (i) cross-sectional % lipid area >65.1% or (ii) % lipid area >32.3 but
<65.1% and plaque area >10.5mm2.
Abbreviations: IB-IVUS, integrated backscatter intravascular ultrasound; RPA, recursive
partitioning analysis; TCFA, thin cap fibroatheroma
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Supplemental Figure 2. Representative OFDI images co-registered to histology
Left column: cross-sectional histologic images of coronary plaques. Mid column: high powered
images of inset box in the left column. Right column: OFDI images co-registered to histology.
Fibrous intima (upper row) appears to be homogeneous bright signals in OFDI. Lipid pool (mid
row) appears to be dark area without clear border. Macrophages (Mø) are seen infiltrating into
the plaque. Sheet of calcium (lower row) appears to be solid black area with clear border.
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Supplemental Figure 3. Fibrocalcific plaque misdiagnosed as lipid-rich by OFDI
Left: cross-sectional histology of fibrocalcific plaque. A large sheet of calcium is present
extending into the deeper regions of the plaque near the media. In the mid column are highpower images of the boxes inset in the left image. Sheet of calcium (Ca++) and macrophage (Mø)
infiltration (red arrowheads) are seen. Right: corresponding image of OFDI. Sheet of calium is
present deep in the plaque is less clear on OFDI as the margins are poorly delineated.
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Supplemental Figure 4. TCFA missed by OFDI
Left: cross-sectional histology of a TCFA with a small area of necrosis (NC). Middle image is a
high power of the box inserted in the left image. Fibrous cap covering the NC is thin <65 µm.
Right: corresponding image of OFDI. OFDI readers missed the regions of the thin fibrous cap
(white arrowhead).
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Supplemental Figure 5. Diagram of pseudo or true OFDI-derived TCFA
In OFDI, macrophages appear high intensity signals with trailing shadow. It is difficult to
correctly diagnose tissues behind macrophages.
Abbreviations: OFDI, optical frequency domain imaging; PIT, pathologic intimal thickening;
TCFA, thin cap fibroatheroma; Th-FA, thick fibroatheroma.
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Supplemental Table 1. IB-IVUS measurement of coronary plaque
IB-IVUS measurement
Histology
IEL area
(mm2)
Lumen
area (mm2)
Plaque
area (mm2)
AIT/Fib
8.9
(6.8, 10.6)
5.9
(4.4, 7.2)
2.6
(2.0, 4.0)
31.9
(24.6, 40.7)
2.8
(1.4, 5.1)
18.0
(13.2, 22.7)
65.7
(60.6, 70.1)
10.6
(7.5, 16.8)
PIT
11.7
(8.4, 15.1)
5.7
(4.2, 8.4)
5.4
(4.0, 7.5)
47.8
(39.9, 54.7)
1.7
(0.9, 3.1)
12.5
(8.6, 16.8)
62.1
(57.4, 66.7)
22.0
(14.4, 30.1)
Th-FA
13.4
(10.1, 18.7)
4.2
(2.9, 7.8)
8.7
(6.9, 11.2)
66.6
(52.4, 73.7)
2.1
(0.8, 4.3)
10.5
(7.4, 14.5)
53.5
(42.9, 61.1)
32.3
(22.4, 43.0)
TCFA
17.2
(10.0, 21.2)
5.7
(2.8, 10.4)
10.6
(8.0, 12.5)
63.8
(49.9, 78.5)
1.1
(0.4, 2.1)
6.6
(3.7, 9.6)
44.6
(34.8, 50.8)
46.8
(39.7, 55.7)
Fibrocalc
10.9
(8.4, 14.1)
4.2
(2.8, 5.7)
7.3
(5.2, 9.2)
61.9
(50.9, 67.6)
10.8
(6.5, 14.3)
19.6
(13.2, 22.5)
53.6
(46.8, 58.2)
15.2
(10.9, 23.3)
<0.001
0.002
<0.001
<0.001
<0.001
<0.001
P value
Plaque
burden (%)
<0.001
% Calc
% Dense fib
% Fib
% Lipid
<.0.001
Values of IB-IVUS measurements are expressed as median (interquartile).
Abbreviations: AIT, adaptive intimal thickening; IB-IVUS, integrated backscatter intravascular ultrasound; IEL, internal elastic
lamina; Fib, fibrous plaque; Fibrocalc, fibrocalcific plaque; PIT, pathologic intimal thickening; TCFA, thin cap fibroatheroma; Th FA,
thick cap fibroatheroma.
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Supplemental Table 2. Positive predictive values of OFDI/IB-IVUS for the detection of
vulnerable plaque
TCFA detection
Positive predictive value
*95% confidence interval
Both by OFDI and IB-IVUS
100.0%
69.2 - 100.0%
Only by OFDI
(non-TCFA by IB-IVUS)
30.8%
9.1 - 61.4%
Only by IB-IVUS
(non-TCFA by OFDI)
14.3%
1.8 - 42.8%
Neither by OFDI nor IB-IVUS
0.6%
0.1 - 1.9%
* 95% confidence interval of nominal variables were calculated by exact binomial probabilities.
Abbreviations: IB-IVUS, integrated backscatter intravascular ultrasound; OFDI, optical
frequency domain imaging; TCFA, thin cap fibroatheroma
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Supplemental methods
Histology Processing for Coronary Arteries
Following intravascular imaging, the hearts were perfusion-fixed with 10% buffered formalin
via the coronary arteries for at least 20 to 30 minutes. Following in situ perfusion of the coronary
arteries, imaged epicardial coronary arteries were removed from the heart and radiographed. If
on radiography calcification was prevalent the vessels were decalcified with EDTA using a
microwave processor. The coronary arteries were segmented at 3 cm intervals, placed in tissue
cassettes and processed through ethanols and xylenes for dehydration. The samples were further
segmented at 3 mm intervals and embedded in a single paraffin block maintaining proximal and
distal orientation. The 1st two slides from each block were stained with hematoxylin-eosin
(H&E) and modified Movat pentachrome stains.
Reproducibility for IB-IVUS measurements
The reproducibility of IB-IVUS measurements was evaluated by Spearman rank correction
coefficient model. To evaluate the intra- and inter-observer agreements, 50 of 360 coronary
sections were randomly selected, in which IB-IVUS measurement was performed. The p values
for correlations of all parameters, including the lumen area, were <0.01 for both the intra- and
inter-observer agreement. Therefore, the IB-IVUS reproducibility is less likely affected by the
lumen contour.
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