A Novel Approach for Quantitative Analysis
of Intracoronary Optical Coherence
Tomography: High Inter-Observer
Agreement With Computer-Assisted
Contour Detection
Shuzou Tanimoto,1 MD, Gaston Rodriguez-Granillo,1 MD, Peter Barlis,1 MBBS, MPH, FRACP,
Sebastiaan de Winter,1 MSc, Nico Bruining,1 PhD, Ronald Hamers,1 PhD, Michiel Knappen,2 PhD,
Stefan Verheye,2 MD, PhD, Patrick W Serruys,1 MD, PhD, and Evelyn Regar,1* MD, PhD
Objective: This study aims to examine observer-related variability of quantitative opti-
cal coherence tomography (OCT) derived measurements from both in vitro and in vivo
pullback data. Background: Intravascular OCT is a new imaging modality using infra-
red light and offering 10 times higher image resolution (15 lm) compared to intravascu-
lar ultrasound. The quantitative analysis of in vivo intracoronary OCT imaging is
complicated by the presence of blood, motion artifacts and the large quantity of infor-
mation that has to be processed. Methods: We developed a standardized, automated
quantification process for intracoronary OCT pullback data with inter-observer variabil-
ity assessed both in vitro by using postmortem human coronary arteries and in vivo by
studying simple and complex coronary pathology and outcomes following stent im-
plantation. The consensus between measurements by two observers was analyzed
using the intraclass and interclass correlation coefficient and the reliability coeffi-
cients. Bland–Altman plots were generated to assess the relationship between variabil-
ity and absolute measurements. Results: In vitro OCT assessment was performed in
nine postmortem coronary arteries. The time needed for semiautomated contour
detection of a 15-mm long coronary segment was
40 min. The absolute and relative
difference between lumen area measurements derived from two observers was low
[0.02 6 0.10 mm2; (0.3 6 0.5)% respectively] with excellent correlation confirmed by
linear regression analysis (R2 5 0.99; P < 0.001). Similarly, in vivo measurements dem-
onstrated a high correlation with the main source of inter-observer variation occurring
as a result of coronary dissection and motion artifact. The absolute and relative
difference between measurements were 0.11 6 0.33 mm2 (1.57 6 0.05)% for
lumen area (R2 5 0.98; P < 0.001), 0.17 6 0.68 mm2 (1.44 6 0.08)% for stent area (R2 5
0.94; P < 0.001), and 0.26 6 0.72 mm2 (14.08 6 0.37)% for neointimal area (R2 5 0.78;
P < 0.001). Conclusions: Highly accurate computer-assisted quantitative analysis
of intracoronary OCT pullbacks is feasible with low inter-observer variability.
The presented approach allows for observer independent analysis of detailed vessel
structures, and may be a valuable tool for future longitudinal studies incorporating
OCT. ' 2008 Wiley-Liss, Inc.
Key words: optical coherence tomography; coronary artery disease; image processing
Conflicts of interest: Ronald Hamers is an employee of CURAD
BV, the Netherlands.
1Department of Cardiology, Thoraxcenter, Erasmus Medical
Center Rotterdam, The Netherlands
2Middelheim Hospital, Antwerp, Belgium
*Correspondence to: E. Regar, MD, PhD, Department of Cardiology,
Thoraxcenter, Room Ba 585, Erasmus Medical Center Rotterdam,
Dr. Molewaterplein 40, 3015 GD Rotterdam, The Netherlands.
E-mail: e.regar@erasmusmc.nl
Received 11 October 2007; Revision accepted 12 December 2007
DOI 10.1002/ccd.21482
Published online 6 March 2008 in Wiley InterScience (www.
interscience.wiley.com).
' 2008 Wiley-Liss, Inc.
Catheterization and Cardiovascular Interventions 72:228–235 (2008)

INTRODUCTION
Optical coherence tomography (OCT) is a light-
based imaging modality that can be used to study bio-
logical tissues in vivo [1]. Recently, the concept of
catheter-based intracoronary OCT has been introduced
[2–4] allowing in vivo imaging of the coronary vessel
wall with a lateral resolution of 15 lm and an axial re-
solution of 25 lm [5]. The currently accepted gold
standard, intravascular ultrasound (IVUS), operates at a
lateral resolution of
120 lm and axial resolution of
80 lm. The unique high-resolution OCT imaging mo-
dality permits the analysis of coronary structures in
greater detail. The measurement accuracy of intracoro-
nary OCT has been established in postmortem human
coronary arteries and showed good correlation to histo-
morphometry [6]. However, compared to ex vivo
imaging, quantitative analysis of in vivo intracoronary
imaging is more complicated due to the presence of
blood and motion artifacts during cardiac cycle. Fur-
thermore, the OCT dataset acquired during motorized
pullback in vivo is much larger than local imaging of
selected cross sections as performed in postmortem
studies. A pullback through the region of interest
(ROI) is necessary in order to visualize the three-
dimensional morphology of the coronary artery. The
present research proposes a standardized automated
quantification process for intracoronary OCT pullback
data. To test its accuracy, inter-observer variability
was assessed in vitro and in vivo including both sim-
ple and complex vessel anatomy, represented by native
coronary arteries before and after stent implantation.
METHODS
OCT Imaging System
We used a commercially available system for intra-
vascular OCT imaging (LightLab Imaging, Westford,
MA). The light source was a 1310-nm broadband
super luminescent diode with an output power in the
range of 8.0 mW. The imaging depth was
1.5 mm
with an axial and lateral resolution of 15 and 25 lm,
respectively. The imaging probe (ImageWireTM Light-
Lab Imaging) had a maximum outer diameter of 0.019
in. and contained a single-mode fiber optic core within
a translucent sheath. The image wire was connected at
its proximal end to the imaging console that permitted
real-time data processing and two-dimensional repre-
sentation of the backscattered light in a cross-sectional
plane. Images were acquired at 15 frames/sec. The
fiber optic core was withdrawn within the catheter
sheath using automated pullback at 1.0 mm/sec.
The accuracy of the OCT system has been recently
reported. Diameters of phantoms with precision-drilled
circular holes were measured in vitro using proprietary
software from LightLab with excellent accuracy
(20.03) and precision (0.02) [7].
Human Coronary Arteries—Postmortem Study
In all cases (n 5 9), the left anterior descending ar-
tery was studied after pressure fixation using 10% buf-
fered formalin. The take off of the first diagonal
branch was used as proximal landmark. Both the prox-
imal and the distal end of the coronary specimen were
sutured to a 6F introducer sheath and positioned in a
saline bath at 378C. The OCT imaging wire was intro-
duced via the proximal sheath into the specimen and
positioned in such a way that the distal OCT catheter
tip was fixed in the distal sheath and an automated
OCT pullback was performed.
Human Coronary Arteries—Clinical Studies
Patients undergoing a stent-implantation procedure
(n 5 10) or a 6-month follow-up angiogram poststent
implantation (n 5 10) were studied. A standard femo-
ral approach with 7F guiding catheters was used. All
patients received weight-adjusted intravenous heparin
in order to maintain the activated clotting time >300
sec and intravenous analgesics before imaging. First, a
dedicated compliant occlusion catheter (Helios, Good-
man, Japan) was introduced into the artery and posi-
tioned proximally to the ROI. The occlusion catheter
allows (a) for limiting the coronary blood flow by very
low-pressure (0.3 atm) inflation of a short (6.0 mm
length) balloon, (b) for simultaneous clearing of the ar-
tery by delivering flush distally to the balloon into the
lumen, and (c) for introduction of the OCT imaging
wire into the artery. After positioning the occlusion
catheter in over the wire technique, the standard
0.014@ guide wire was withdrawn, and the OCT imag-
ing wire introduced via the central lumen distal into
the target vessel. An automated OCT pullback was
then performed. During OCT image acquisition, the ar-
tery was cleared with lactated Ringer’s solution (flow
rate 0.5 ml/sec; temperature 378C). Sufficient occlusion
of the lumen was documented by contrast injection via
the guiding catheter and the balloon pressure increased
to 0.5 atm if necessary.
Quantitative OCT
The digitized tomographic OCT image dataset was
transformed from digital movie file format (AVI) into
the medical DICOM image standard and stored onto a
picture archiving system. Quantitative OCT (QOCT)
analysis was performed using dedicated software
(CURAD vessel analysis, CURAD BV, Wijk bij Duur-
stede, Netherlands) [8] (Fig. 1). Every third frame of
the pullback of long segments was entered. This
Quantitative OCT Analysis 229
Catheterization and Cardiovascular Interventions DOI 10.1002/ccd.
Published on behalf of The Society for Cardiovascular Angiography and Interventions (SCAI).