Mailing address: Yoshinobu Onuma, MD, Department of Interventional ... The impact of the sampling rate (SR) of optical frequency domain imaging (OFDI) on ...
ORIGINAL ARTICLE
Circulation Journal Official Journal of the Japanese Circulation Society http://www. j-circ.or.jp
Imaging
Quantitative Optical Frequency Domain Imaging Assessment of In-Stent Structures in Patients With ST-Segment Elevation Myocardial Infarction – Impact of Imaging Sampling Rate – Takashi Muramatsu, MD, PhD; Hector M. García-García, MD, PhD; Il Soo Lee, MD, PhD; Nico Bruining, PhD; Yoshinobu Onuma, MD; Patrick W. Serruys, MD, PhD
Background: The impact of the sampling rate (SR) of optical frequency domain imaging (OFDI) on quantitative assessment of in-stent structures (ISS) such as plaque prolapse and thrombus remains unexplored. Methods and Results: OFDI after stenting was performed in ST-segment elevation myocardial infarction (STEMI) patients using a TERUMO OFDI system (Terumo Europe, Leuven, Belgium) with 160 frames/s and pullback speed of 20 mm/s. A total of 126 stented segments were analyzed. ISS were classified as either attached or non-attached to stent area boundaries. The volume, mean area and largest area of ISS were assessed according to 4 frequencies of SR, corresponding to distances between the analyzed frames of 0.125, 0.25, 0.50 and 1.0 mm. ISS volume was calculated by integrating cross-sectional ISS areas multiplied by each sampling distance using the disk summation method. The volume and mean area of ISS became significantly larger, while the largest area became significantly smaller as sampling distance became larger (1.11 mm2 for 0.125 mm vs. 1.00 mm2 for 1.0 mm, P for trend=0.036). In addition, variance of difference was positively associated with increasing width of sampling distance. Conclusions: Quantification of ISS is significantly influenced by the applied frequency of SR. This should be taken into account when designing future OFDI studies in which quantitative assessment of ISS is critical for the evaluation of STEMI patients. (Circ J 2012; 76: 2822 – 2831) Key Words: Acute myocardial infarction; Coronary artery disease; Coronary thrombosis; Optical coherence tomography; Prolapse
I
ntravascular optical coherence tomography (OCT) is a light-based imaging modality that provides high-resolution images of the coronary arteries.1–3 The recently developed optical frequency domain imaging (OFDI) technique, or Fourier-domain OCT, provides higher image acquisition speed, greater penetration depth, and higher-quality image resolution compared to the conventional time-domain OCT.4–7 Furthermore, its higher frame rate and higher pullback speed reduce the impact of possible motion artifacts and improve longitudinal resolution, facilitating a more detailed depiction and more accurate quantitative analysis of coronary arteries compared to the time-domain OCT.8,9 Recent OCT/OFDI studies applied various sampling rates (SRs) for qualitative and quantitative cross-sectional image analysis. The SR, which can be translated into the distance be-
tween 2 sampled frames along the longitudinal axis (ie, sampling distance), varied from 0.33 to 1.0 mm.10–14 Interestingly, a previous study demonstrated that lumen and stent areas showed low variability (30%) or pre-procedural TIMI flow grade ≤2 in a single de novo, native, unstented vessel were considered for enrollment. Patients were randomized in a 1:1 fashion to receive either primary percutaneous coronary intervention (PCI) with thrombectomy (n=71) or without thrombectomy (n=70) prior to biolimus-A9 eluting metallic stent (Nobori®; Terumo Europe, Leuven, Belgium) implantation. The primary endpoint was defined as post-procedural minimal flow area quantified on OFDI. In this substudy, the OFDI data were pooled regardless of the treatment arm. This study protocol was approved by the local ethics committee at each participating center, and written informed con-
sent was obtained from all enrolled patients. Image Acquisition The primary PCI procedure was performed using a 6-Fr guiding catheter. As long as the patient’s hemodynamics were stable, 0.2 mg i.c. nitroglycerin was given before the OFDI procedure. This imaging procedure was performed with a TERUMO OFDI system (Terumo Europe, Leuven, Belgium) using a nonocclusive technique at an image acquisition rate of 160 frames/s during an automated pullback at a speed of 20 mm/s. The pullback was performed during continuous i.c. injection of contrast medium through the guiding catheter using an injection pump at a flow rate of 3–4 ml/s for a maximum of 4 s. The imaging data once saved in the console were converted into AVI files and then transferred for off-line quantitative analysis. Definition of In-Stent Structure and Contour Detection The region of interest (ROI) was selected as the stented segment, which was defined as the region between the first and the last frame where metallic stent struts were visible around the whole vessel circumference.7 Quantitative analysis software (QCU-CMS version 4.50; LKEB, Leiden University, Leiden, The Netherlands) was used for off-line OFDI analysis. In each cross-section, we analyzed all individual masses within the stent area, which was defined as in-stent structure (ISS). In cases of incomplete stent apposition, masses located
Circulation Journal Vol.76, December 2012
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MURAMATSU T et al.
Figure 2. Example of sampling frames and volumetric assessment. (A) Focally protruding mass is shown on longitudinal view (blue box). (B) In the magnified image, each cross-section is numbered and indicated by yellow and white lines. (C) Cross-sectional area analysis was performed in all frames (sampling distance of 0.125 mm), every 3rd frame (0.25 mm), every 5th frame (0.50 mm), and every 9th frame (1.0 mm). (D) Schematic representation of volumetric estimation of in-stent structure (ISS) for corresponding sampling distance. ISS volume can be calculated by numerical integration of cross-sectional area multiplied by corresponding sampling distance (disk summation method). The estimated ISS volume can be expressed as the total bar (disk) area.
Circulation Journal Vol.76, December 2012
OFDI Quantification of Intraluminal Mass
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Table 1. Frames With ISS vs. Sampling Rate
No. analyzed frames
0.125 mm
0.25 mm
0.5 mm
1.0 mm
21,703
10,887
5,475
2,770
14,269 (65.7)
7,247 (66.6)
3,722 (68.0)
1,986 (71.7)
1,657 (7.6)
835 (7.7)
430 (7.9)
242 (8.7)
14,513 (66.9)
7,383 (67.8)
3,808 (69.6)
2,044 (73.8)
P for trend†
No. frames with ISS Attached Non-attached Any No. sub-segments with ISS Attached
923
654
430
293
Non-attached
308
139
61
39
Any
878
633
413
284
113.3±53.1
57.5±26.7
29.5±13.4
15.8±7.1
