Frequency-Domain Intravascular Optical Coherence Tomography of the Femoropopliteal Artery

Transcription

1 Cardiovasc Intervent Radiol (2011) 34: DOI /s CLINICAL INVESTIGATION Frequency-Domain Intravascular Optical Coherence Tomography of the Femoropopliteal Artery Dimitris Karnabatidis Konstantinos Katsanos Ioannis Paraskevopoulos Athanasios Diamantopoulos Stavros Spiliopoulos Dimitris Siablis Received: 29 September 2010 / Accepted: 7 December 2010 / Published online: 30 December 2010 Ó Springer Science+Business Media, LLC and the Cardiovascular and Interventional Radiological Society of Europe (CIRSE) 2010 Abstract Purpose Optical coherence tomography (OCT) is a catheter-based imaging method that employs near-infrared light to produce high-resolution intravascular images. The authors report the safety and feasibility and illustrate common imaging findings of frequency-domain OCT (FD-OCT) imaging of the femoropopliteal artery in a series of 20 patients who underwent infrainguinal angioplasty. Methods After crossing the lesion of interest, OCT was performed with a dextrose saline flush technique with simultaneous obstructive manual groin compression. An automatic pullback FD-OCT device was employed (each scan acquiring 54 mm of vessel lumen in 271 consecutive frames). OCT images were acquired before and after balloon dilatation and following provisional stenting if necessary and were evaluated for baseline characteristics of plaque or in-stent restenosis (ISR), vessel wall trauma after angioplasty, presence of thrombus, stent apposition, and tissue prolapse. Imaging follow-up was not included in this study s protocol. Results Twenty-seven obstructive lesions (18 cases of de novo atherosclerosis and 9 of ISR) of the femoropopliteal artery were imaged and 148 acquisitions were analyzed in total. High-resolution intravascular OCT imaging with effective blood clearance was achieved in 93.9%. Failure Electronic supplementary material The online version of this article (doi: /s ) contains supplementary material, which is available to authorized users. D. Karnabatidis (&) K. Katsanos I. Paraskevopoulos A. Diamantopoulos S. Spiliopoulos D. Siablis Department of Radiology, School of Medicine, Patras University Hospital, Patras 26504, Greece karnaby@upatras.gr was mainly attributed to preocclusive proximal lesions and/ or collateral flow. Mixed features of lipid pool areas, calcium deposits, necrotic core, and fibrosis were identified in all of the imaged atherosclerotic lesions, whereas ISR was purely fibrotic. After balloon angioplasty, OCT identified extensive intimal tears in all cases and one case of severe dissection that biplane subtraction angiography failed to identify. Conclusions Infrainguinal frequency-domain optical coherence tomography is safe and feasible and may provide intravascular high-resolution imaging of the femoropopliteal artery during infrainguinal angioplasty procedures. Keywords Femoropopliteal Infrainguinal Frequency-domain Optical coherence tomography (OCT) Angioplasty Stent Atherosclerotic plaque Dissection Thrombus Introduction Optical coherence tomography (OCT) was introduced for intravascular imaging of the coronary arteries during the early 1990s. In the European Union, the first OCT catheter was approved for coronary artery imaging in 2004 [1, 2]. OCT incorporates emission of near-infrared light and advanced optical engineering to produce high-resolution cross-sectional images of the artery lumen and wall. As in ultrasound technology, emitted light energy is reflected and attenuated according to tissue texture. Generally, OCT systems produce cross-sectional vessel images by measuring the depth of light reflections based on the round-trip propagation time of the reflected light energy [1, 3, 4]. First-generation OCT systems employed a broadband light source ( nm) and time-domain interferometry

2 D. Karnabatidis et al.: Infrainguinal Optical Coherence Tomography 1173 analysis for image reconstruction. However, time-domain algorithms were not fast enough and provided limited radius of effective field of view. Lumen imaging was limited to 3- to 4-mm vessels, such as coronary arteries, and typically vessel segments no more than 2-cm long could be imaged. Newgeneration OCT systems utilize a light source with variable wavelength that is tuned to continuously oscillate between 1250 and 1350 nm, a so-called wavelength swept laser, and frequency-domain interferometry analysis (FD-OCT) to achieve faster image acquisition and greater scan depths. As the wavelength of the laser-emitted electromagnetic radiation oscillates, reflections from refractive-index discontinuities produced by variable tissue depth and texture generate frequency interference signals, which are further analyzed with Fourier transformation to produce a two-dimensional crosssectional image of the vessel lumen [1, 2]. In contrast to conventional digital angiography and intravascular ultrasound, which can characterize vessel anatomy and morphology but are unable to visualize microscopic details of atherosclerotic plaque, intimal dissections, stent apposition, and neointimal hyperplasia on a size scale B100 lm [5], OCT can readily visualize vessel microstructure at a 10- to 20-lm resolution with exquisite detail [1, 4, 6, 7]. Among others, OCT imaging of the coronary arteries has been applied for identification of vulnerable plaque morphology, quantification of in-stent neointimal hyperplasia, longitudinal follow-up of stent endothelialization, and depiction of stent strut malapposition within the context of observational studies [8 10]. A variety of studies have validated the correlation of OCT findings versus standard histology [8, 11 14]. To date, however, applicability of the method has been limited to small diameter arteries (B4 mm) [1 3]. Compared with older time-domain versions of the technology, new-generation frequency-domain OCT (FD-OCT) can achieve faster intravascular OCT imaging with a greater scan depth suitable for the peripheral arteries with diameter C4 mm [2]. The authors report the safety and feasibility and illustrate common imaging findings of FD-OCT for in-vivo intravascular imaging of the superficial femoral artery during infrainguinal angioplasty procedures. Material and Methods Patient Cohort The study was institutional review board-approved by the hospital s Scientific and Ethical Committee, and all patients signed an informed consent form before enrollment in the study. Standard antegrade access was obtained in the common femoral artery using bone landmarks and/or ultrasound guidance. All patients received 5,000 IU of heparin during angioplasty and were on dual antiplatelet therapy with 100 mg of aspirin and 75 mg of clopidogrel daily for at least 3 days before the procedure. A 6-Fr x 15-cm vascular sheath (Terumo, Japan) was introduced and the obstructive lesion of interest was negotiated using a combination of routine guidewires and supporting 4-Fr straight or angled hydrophilic catheters. Intraluminal recanalization was performed in case of a chronic total occlusion. Cases with diffuse cylindrical calcifications of the femoral artery or subintimal passage with the loop technique were a priori excluded from the study. The guidewire was then exchanged for a standard guidewire to allow introduction of the optical fiber. After baseline OCT imaging, lesions were treated with balloon dilatation and further bailout stenting if deemed necessary. Indications for bailout stenting included a suboptimal angioplasty result or elastic recoil or flow-limiting dissection resulting in [30% residual stenosis on visual DSA estimate or quantitative OCT analysis. In case of stenting, nitinol self-expanding stents oversized by approximately 1 mm with respect to reference vessel size were chosen. Selective single-plane digital subtraction angiography (DSA) was performed before and after each OCT acquisition to evaluate for vessel spasm, thrombosis, or other local complication. A second DSA with a different projection angle ([45 difference) was performed only in case of a significant stenosis or dissection detected by OCT but not identified by previous DSA. A final DSA run of the infrapopliteal arteries was taken and compared to preprocedural imaging to exclude distal atherothrombotic embolism. FD-OCT Optical coherence tomography is a catheter-based intravascular imaging method that employs near-infrared light to produce high-resolution images of the vessel lumen and wall. An in-depth analysis of intravascular OCT technology may be found elsewhere [2, 4, 7]. FD-OCT of the femoral artery was performed with a recently available commercial system (C7-XR, Lightlab, Massachusetts, USA). OCT was performed with a dextrose saline flush (glucose 5% w/v) technique with simultaneous manual obstruction of the common femoral artery. The dextrose flush was administered through the 6-Fr sheath s side-port with an automated injector pump. Infusion settings were adjusted at a total volume of 50 ml, an injection rate of 10 ml/s and a maximum pressure of 400 psi. In case of diabetic patients, short-acting insulin was coadministered to correct blood hyperglycemia as necessary. An automatic pullback FD-OCT device was employed with each scan acquiring 54 mm of vessel lumen in 271 consecutive frames. Scan parameters are outlined in detail in Table 1.

3 1174 D. Karnabatidis et al.: Infrainguinal Optical Coherence Tomography Table 1 OCT technical details Femoral sheath size 6-Fr x cm Guidewire size compatible Injector pump Automated electronic injector (Medrad, Warrendale, USA) Flush medium Dextrose 5% w/v Flush volume 50 ml Flush injection rate 10 ml/sec Injection pressure Max. 400 psi Vessel obstruction Proximal manual obstruction of the common femoral artery OCT catheter Monorail optical fiber (C7-XR, Lightlab, Massachusetts, USA) OCT technology Frequency-domain image reconstruction Light wavelength nm Working channel 3.7-Fr ( wire plus the catheter with the optical fiber) Axial resolution lm Lateral resolution lm (depending on pullback speed) Scan diameter 3 8 mm (8.3 mm in saline) Max pullback speed 20 mm/s Acquisition length 54 mm Acquisition time 2.7 s Frame rate 100 f/s No. of frames 271 OCT images were acquired before and after balloon dilatation and following provisional stenting. The extra procedural time required for each femoral OCT acquisition was recorded. Image Analysis All acquisitions were digitally archived and further evaluated for baseline findings of plaque or ISR, vessel wall trauma after angioplasty, presence of thrombus, apposition of stent struts, and tissue prolapse. Description of imaging findings adhered to widely accepted morphological criteria of cardiovascular OCT in correlation with histology as described elsewhere [2, 6, 8, 15 17]. Briefly, the main properties that describe tissue composition under OCT imaging are attenuation and backscattering. Light attenuation determines the penetration depth of the emitted light beam. For example, lipid-rich plaques and organized red thrombus are highly attenuating tissues and limit light penetration. Backscattering refers to light propagation within tissues and produces bright signal-rich areas, such as in the case of fibrotic neointimal hyperplasia. The morphological characteristics of different plaque types and other findings were described depending on the respective attenuation and backscattering behavior. Both axial images and longitudinal reconstructed views on two rotating orthogonal projections were analyzed (Lightlab software). Anatomical localization of intravascular OCT findings for further correlation and comparison with respective DSA runs was performed with the aid of a radiopaque ruler. All images were reviewed by two senior vascular interventional radiologists with more than 10 years of experience, and a consensus was reached in case of ambiguity. Statistical Analysis Discrete variables were expressed as counts and percentages and continuous variables were given as medians and interquartile ranges (i.e., between the 25th and 75th percentiles) in parentheses or as means ± standard deviation (SD) if they passed the normality test. The unpaired Student s t test was used to test the significance of difference of variables that passed the normality test. The Mann- Whitney U test was used for qualitative variables and for nonparametric testing of continuous variables that did not pass the normality test. Statistical analysis was performed with use of the SPSS/PASW statistical software package (version 17.0; SPSS/PASW, Chicago, IL). The threshold of statistical significance was set for a P value of Results Safety and Feasibility In total, 20 patients with atherosclerotic arterial disease of the femoropopliteal artery treated with percutaneous angioplasty and provisional stenting for lifestyle-limiting claudication or critical limb ischemia were included in the study (Table 2). Twenty-seven obstructive lesions (mean lesion length 5.3 ± 2.2 cm) involving primarily TASC IIA and IIB lesions of de novo atherosclerosis (n = 18) or ISR

4 D. Karnabatidis et al.: Infrainguinal Optical Coherence Tomography 1175 Table 2 Baseline demographics and lesion characteristics (%) Patients 20 (100) Male: gender 16/20 (80) Smoking history 15/20 (75) Hyperlipidemia 13/20 (65) Diabetes 9/20 (45) Renal disease (Crea [2.5 mg/dl) 2/20 (10) Rutherford stage (median and IQR) 3 (3-3) Lifestyle-limiting claudication 16/20 (20) Critical limb ischemia 4/20 (20) Lesions 27 (100) TASC IIA 7/27 (25.9) TASC IIB 17/27 (63) TASC IIC 3/27 (11.1) TASC IID 0/27 (0) Lesion length (cm) 5.3 ± 2.2 Chronic total occlusions 3/27 (11.1) Lesion calcifications 5/27 (18.5) ISR 9/27 (33.3) (ISR; n = 9) of the femoropopliteal artery were imaged. In total, 148 OCT scans were acquired preangioplasty (n = 68), postangioplasty (n = 47), and after stenting (n = 33), and 40,108 frames were analyzed. High-quality intravascular OCT imaging with effective blood clearance during the whole pullback length was achieved in 93.9% (139/148) of the scans. Failure was mainly attributed to preocclusive proximal lesions and/or collateral flow prohibiting effective flushing. Catheter dysfunction occurred in two cases and was attributed to a broken optical fiber during manual pressure of the groin because of patient obesity causing excessive angulation of the vascular access sheath. No adverse event was noted due to this dysfunction. The rest of the procedures were free of any local complications including spasm, vessel thrombosis, and distal embolism. Extra procedural time was 7.2 ± 3.1 min/oct scan adding up an average extra total time of approximately 50 min/patient. Transient rest pain or a burning sensation that lasted \10 s was reported by two patients immediately after the obstructive dextrose saline flush in 7.4% (11/148) of the OCT sessions. There were no distal embolic events and no other hemodynamic complications occurred. On a frame-by-frame basis, the rate of successful visualization of 100% of the vessel lumen circumference was 87.9% (35,295/40,108). Eccentric wire position was the main cause for incomplete imaging of vessel wall circumference. Imaging Findings The whole variety of usual OCT artifacts was noted affecting 12.2% of the acquired scans (18/148). The most frequently observed artifacts included incomplete blood displacement, sew-up artifact as a result of wire instability, and fold-over artifact the latter was characteristic of newgeneration FD-OCT systems. Quantitative lumen analysis of arteries with diameter up to 7 mm was performed. Mixed features of lipid pool areas, calcium deposits and calcified plaques, necrotic areas, and fibrosis were identified in all of the imaged atherosclerotic lesions (Fig. 1). However, based on the predominant baseline imaging findings, lesions under investigation were classified as purely fibrotic in 27.7% (5/18), fibrocalcific in 44.4% (8/ 18), mostly lipid-laden in 16.6% (3/18), and necrotic/calcified in 11.1% (2/18). Intraplaque accumulation of macrophages was noted in 11.1% (2/18) of de novo atheromatic lesions. Varying degrees of neointimal hyperplasia were demonstrated in all cases of ISR lesions (n = 9) with purely fibrotic features and considerable neovascularization in two of them (22.2%; 2/9; Figs. 1, 2). The latter finding coincided with the level of maximum vessel stenosis in both cases. In one case, a second lumen along with a reentry zone was identified and was attributed to accidental subintimal crossing of a total chronic proximal popliteal occlusion (Fig. 3). After balloon angioplasty, OCT identified extensive minor intimal tears in all cases (100%) of both de novo lesions (Fig. 4) and ISR cases (Fig. 5). Significant dissection with severe lumen compromise mandating stent placement was detected in 27.7% (5/18) of the de novo atherosclerotic cases. Single-plane subtraction angiography failed to identify 60% (3/5) of severe postangioplasty dissection cases, whereas repeat DSA on a second projection plane failed to visualize 20% (1/5) of them (Fig. 6). Dissections were treated by self-expanding stents oversized by approximately 1 mm compared with reference vessel diameter on DSA. Segmental intrastent tissue prolapse and strut malapposition were noticed in 40% (2/5) and 60% (3/ 5) of the newly implanted self-expanding stents, respectively. Platelet-rich white thrombus was observed on the strut surface of one popliteal stent immediately postplacement, despite routine patient heparinization (Fig. 7). In the same case, OCT depicted incomplete stenting of the distal part of the dissection flap and a second selfexpanding stent was implanted to achieve full lesion coverage. The observed rates of the various imaging findings at baseline, after angioplasty, and after provisional stenting are outlined in detail in Table 3. Discussion The authors investigated the feasibility and applicability of FD-OCT for high-resolution intravascular imaging of the superficial femoral artery during percutaneous infrainguinal

5 1176 D. Karnabatidis et al.: Infrainguinal Optical Coherence Tomography Fig. 1 Examples of FD-OCT imaging. A Quantitative vascular analysis of ISR, including vessel diameter stenosis (% DS) and vessel area stenosis (% AS). B Fibrocalcific plaque of the femoral artery detected in the right upper image quadrant. Note the welldefined hypoattenuating calcified deposit (white asterisk) covered by a homogeneous signal-rich fibrotic intimal cap. C One-year follow-up of femoral stent shows an area of fully endothelialized stent mesh angioplasty procedures. FD-OCT can achieve significantly faster pullback speeds during image acquisition than conventional time-domain OCT (up to 20 mm/sec), which is elemental for high-quality imaging of longer segments and larger caliber arteries, such as the femoral arteries. In addition, extremely fast image acquisition is necessary to reduce the time interval and flushing bolus necessary for blood replacement and thereby minimize the effective time of tissue ischemia [1, 2]. The only alternative high resolution endovascular imaging modality in today s clinical use is intravascular ultrasound (IVUS). According to the literature, comparison between the older OCT technology and high-frequency IVUS in clinical and in vivo studies has demonstrated that OCT provides description of the vascular structural features with improved quality and finer detail, by means of its with minimal hyperplasia (each stent strut is impermeable to light and produces a characteristic shadow. Note an area of overlapping stent struts (white arrows). D Progressive ISR with multilayer appearance of neointimal hyperplasia. A superficial layer of low-signal myxomatous hyperplasia (neointimal hyperplasia containing proteoglycan-rich extracellular matrix) and a deeper level of signal-rich hypoattenuating fibrotic hyperplasia are detected higher axial resolution [5, 6, 18]. Introduction of FD-OCT technology has additionally improved the speed and quality of imaging acquisition compared with IVUS. Experience with FD-OCT has been accumulating since late 2007, when it was first tested in the coronary arteries of 25 patients with a nonocclusive contrast flush technique and an average of two pullback sessions per patient [1]. To our knowledge, this is the first report of FD-OCT application in the infrainguinal arteries. According to our findings, acquisition of OCT is severely compromised in case of an overlying proximal preocclusive lesion or high-grade stenosis (patent lumen diameter \1.5 mm) prohibiting effective flushing and blood clearance of the lumen. In addition, the OCT fiber itself requires a 3.7-Fr working channel, which further obstructs the lumen. OCT imaging is further degraded by exuberant blood backflow from side-branches

6 D. Karnabatidis et al.: Infrainguinal Optical Coherence Tomography 1177 Fig. 2 Neointimal neovascularization. A Homogeneous signal-rich fibrotic concentric restenosis of the midfemoral artery 9 months after previous balloon angioplasty. Note the area of neovascularized tissue in the right lower image quadrant (white arrows). B Example of neointimal neovascularization (white arrows) within ISR. Neointimal neovascularization is related to increased vessel restenosis Fig. 3 Subintimal reentry zone. A D Stacked consecutive axial OCT images of an accidental subintimal recanalization (lateral resolution 800 lm). Guidewire and optical fiber are located in the false lumen. Note the tear of the dissection flap creating a communication channel between the false and the true lumen (white asterisk) or collaterals. Therefore, we would recommend predilation with an undersized balloon in case of chronic total occlusions to facilitate acquisition of high-quality OCT scans. The performance of femoral OCT through a retrograde cross-over approach from the contralateral groin was not explored. However, it is plausible that using a long sheath

7 1178 D. Karnabatidis et al.: Infrainguinal Optical Coherence Tomography Fig. 4 Angioplasty barotrauma. A Mural thrombus containing both hypoattenuating (white thrombus) and hyperattenuating (red thrombus) elements is located in the left lower image quadrant. B Postangioplasty rupture of the vessel wall media (white arrows). C Almost circumferential medial rupture producing two parallel false lumens (white asterisks). Such findings would appear as minor intimal tears on conventional angiogram because of superimposed areas of contrast filling (Color figure online) Fig. 5 ISR angioplasty. A Baseline OCT imaging of ISR before balloon angioplasty. Note an area of increased neovascularity (white arrows). B Same level after balloon angioplasty. Typical OCT image of post-pta barotrauma with irregular interruptions and tears of the neointima to cannulate the contralateral superficial femoral artery and provided that the aortic bifurcation does not have a steep angle, which might prohibit advancement of the fiber or even break it, similar results could be expected with concomitant manual compression of the contralateral groin. Company guidelines suggest a nonocclusive image acquisition technique with contrast or contrast/saline flushing at a constant rate less than 4 ml/s for 2 3 s based on experimental data and experience from the coronary practice where all major coronary branches could be consistently imaged in this way [1]. However, in contrast to coronary practice where continuous flushing is the accepted method of choice for routine OCT practice [19], we found that this technique is inadequate for large muscular arteries, such as the infrainguinal femoral artery and the popliteal artery, presumably because of the higher blood flow rate and the more extensive collateral networks. We consider proximal vessel obstruction with manual groin compression, like an operator would routinely do for hemostasis, an integral part of a successful automated saline flush to clear the target vessel lumen. In our experience, combining the technique of dextrose saline flush with manual compression of the groin, several OCT scans of the peripheral arteries can be obtained without any risk of contrast induced nephropathy or fluid overload, both of which are extremely important in the setting of patient cohorts with major comorbidities, such as diabetes, heart failure, or other cardiovascular disorders. Logically, the same technique also can be applied with a guide catheter, which can be placed in close proximity with the target lesion. The transient ischemic pain mentioned by two patients during OCT acquisition may be primarily attributed in the high-volume saline flush and temporary blood replacement and secondly in obstructive groin compression. According to our findings, intravascular OCT imaging during infrainguinal angioplasty procedures was beneficial not only in characterizing the morphology of atherosclerotic plaques and ISR but also in detailed evaluation of the

8 D. Karnabatidis et al.: Infrainguinal Optical Coherence Tomography 1179 Fig. 6 Missed dissection flap. A Baseline angiogram of a symptomatic TASC IIA concentric popliteal stenosis (black arrowhead). B Transluminal angioplasty with a 5-mm balloon catheter. C Immediate follow-up angiogram demonstrates brisk contrast flow with minor irregularities of the lumen wall. D Repeat angiogram on a steeper medial angle clearly delineated a severe postangioplasty dissection flap that was further treated with a 6-mm self-expanding stent. E Baseline OCT image shows the signal-rich features of the peripheral arteries after balloon angioplasty and provisional stenting. High-resolution OCT images provided exquisite two-dimensional axial and longitudinal views of the femoropopliteal artery and allowed thorough investigation of a variety of angioplasty sequela, including and not limited to intimal tears and dissection flaps, white and red thrombus, stent mesh malapposition, and intrastent plaque prolapse. Of interest, OCT identified three cases of suboptimal postangioplasty outcome that single-plane subtraction angiography did not recognize and accounted for 60% (3/5) of the whole dissection caseload in our series. Although an angiogram on a second projection plane is usually sufficient for all cases of dissection or residual stenosis, this is not routinely exercised because of increased contrast load and risk of contrast-induced nephropathy. It is therefore plausible that OCT may have a future role in detailed three-dimensional intravascular imaging of the peripheral arteries for better understanding of angioplasty immediate and late outcomes. However, fibrotic concentric lesion. F Postangioplasty OCT clearly shows a suboptimal angioplasty result with dissection and severe luminal compromise that was initially missed in the corresponding angiogram of image (C) above (OCT imaging included the vessel segment in the dotted black box of images C and D). G Final OCT imaging after selfexpanding stent placement demonstrates effective restoration of popliteal artery lumen (widest diameter measures up to 5.5 mm) repeat imaging follow-up was not included in this study s protocol. Another limitation of this study was the fact that a cost-effectiveness analysis was not performed. Taking into consideration both the high cost of the device and the fact that a second projection usually clarifies the diagnosis of residual stenosis in the majority of the cases, the clinical application of this intravascular imaging modality can be further disputed. Furthermore, the groin manual compression maneuver that was performed to acquire proper blood clearance of the target vessels could theoretically cause acute thrombosis, especially in cases of long obstructive lesions with impaired run-off. However, this was not encountered in this study because the compression maneuver lasted only for a few seconds during each OCT acquisition. Considering the fact that the femoropopliteal artery is notorious for its unique biomechanical environment and high restenosis rates contributing to early vessel failure, incorporation of OCT into modern trials of femoral angioplasty

9 1180 D. Karnabatidis et al.: Infrainguinal Optical Coherence Tomography Fig. 7 Stent thrombus. A Immediate deposition of hypoattenuating fibrin-rich white thrombus on the strut mesh of a self-expanding stent was identified on postimplantation OCT scan. Note the magnified view of three malapposed stent struts fully covered by fibrin in the left upper image quadrant. B OCT image of the same stent on a more distal level demonstrates intrastent plaque protrusion (sharply defined elements with increased backscattering correspond to a mixture of calcium, lipid and necrotic core) causing stent malapposition. Stent struts and protruding plaque are circumferentially covered by a thin irregular layer of white thrombus Table 3 Imaging findings (%) Technical results (n = 148 scans; 40,108 frames) Successful OCT acquisition 139/148 (93.9) Technical failure (broken optical fiber) 2/148 (1.4) Whole-diameter vessel lumen imaging 35,295/40,108 (87.9) Artifacts 18/148 (12.2) Extra procedural time per OCT scan (min) 7.2 ± 3.1 Baseline imaging findings (n = 27) Maximum vessel area stenosis (%) 75.9 ± 12.2 Maximum vessel diameter stenosis (%) 61.5 ± 11.3 ISR lumen loss (mm) 2.1 ± 0.3 Fibrotic plaque 5/18 (27.7) Fibrocalcific plaque 8/18 (44.4) Lipid pool plaque 3/18 (16.6) Necrotic/calcified plaque 2/18 (11.1) Macrophage accumulation 2/18 (11.1) In-stent neointimal hyperplasia 9/9 (100) Neointimal neovascularization 2/9 (22.2) Post-angioplasty findings (n = 27) Organized red thrombus 2/27 (7.4) Fibrin/platelet-rich white thrombus 7/27 (25.9) Media rupture 3/27 (11.1) Minor intimal tears 27/27 (100) Severe intimal dissection ([30%) 5/27 (18.5) Post-stenting findings (n = 5) Intra-stent tissue prolapse 2/5 (40) Stent strut malapposition 3/5 (60) Stent thrombus 1/5 (20) Incomplete flap coverage 1/5 (20)

10 D. Karnabatidis et al.: Infrainguinal Optical Coherence Tomography 1181 and stenting may provide further insights into the progression of atherosclerotic disease and vessel restenosis. OCT is highly advantageous in the longitudinal evaluation of stents, because it may provide serial follow-up imaging on a strutby-strut basis and visualize thrombus, malapposition, and endothelialization with high conspicuity. In conclusion, FD-OCT is an optimal experimental tool for the evaluation of atherosclerotic disease progression and vessel restenosis. Moreover, it may provide intravascular high-resolution imaging of the superficial femoral artery during infrainguinal angioplasty procedures and could prove clinically useful for the determination of intrastent tissue prolapse and strut malapposition. Nonetheless, it should not be utilized as a tool for routine clinical practice until evidence from further clinical trials emerge to determine the specific indications for OCT imaging of the peripheral arteries. Conflict of Interest of interest. References The authors declare that they have no conflict 1. Barlis P, Schmitt JM (2009) Current and future developments in intracoronary optical coherence tomography imaging. EuroIntervention 4(4): Bezerra HG, Costa MA, Guagliumi G, Rollins AM, Simon DI (2009) Intracoronary optical coherence tomography: a comprehensive review clinical and research applications. JACC Cardiovasc Interv 2(11): Barlis P, Di Mario C, van Beusekom H, Gonzalo N, Regar E (2008) Novelties in cardiac imaging-optical coherence tomography (OCT). EuroIntervention 4(Suppl C):C22 C26 4. Low AF, Tearney GJ, Bouma BE, Jang IK (2006) Technology Insight: optical coherence tomography-current status and future development. Nat Clin Pract Cardiovasc Med 3(3): quiz Bouma BE, Tearney GJ, Yabushita H et al (2003) Evaluation of intracoronary stenting by intravascular optical coherence tomography. Heart 89(3): Low AF, Kawase Y, Chan YH, Tearney GJ, Bouma BE, Jang IK (2009) In vivo characterisation of coronary plaques with conventional grey-scale intravascular ultrasound: correlation with optical coherence tomography. EuroIntervention 4(5): Wolbarst AB, Hendee WR (2006) Evolving and experimental technologies in medical imaging. Radiology 238(1): Yabushita H, Bouma BE, Houser SL et al (2002) Characterization of human atherosclerosis by optical coherence tomography. Circulation 106(13): Sawada T, Shite J, Shinke T et al (2006) Persistent malapposition after implantation of sirolimus-eluting stent into intramural coronary hematoma: optical coherence tomography observations. Circ J 70(11): Bonnema GT, Cardinal KO, Williams SK, Barton JK (2008) An automatic algorithm for detecting stent endothelialization from volumetric optical coherence tomography datasets. Phys Med Biol 53(12): Brezinski ME, Tearney GJ, Bouma B et al (1998) Optical biopsy with optical coherence tomography. Ann NY Acad Sci 838: Brezinski ME, Tearney GJ, Boppart SA, Swanson EA, Southern JF, Fujimoto JG (1997) Optical biopsy with optical coherence tomography: feasibility for surgical diagnostics. J Surg Res 71(1): Brezinski ME, Tearney GJ, Bouma BE et al (1996) Optical coherence tomography for optical biopsy. Properties and demonstration of vascular pathology. Circulation 93(6): Prabhudesai V, Phelan C, Yang Y, Wang RK, Cowling MG (2006) The potential role of optical coherence tomography in the evaluation of vulnerable carotid atheromatous plaques: a pilot study. Cardiovasc Intervent Radiol 29(6): Jang IK, Bouma BE, Kang DH et al (2002) Visualization of coronary atherosclerotic plaques in patients using optical coherence tomography: comparison with intravascular ultrasound. J Am Coll Cardiol 39(4): Jang IK, Tearney GJ, MacNeill B et al (2005) In vivo characterization of coronary atherosclerotic plaque by use of optical coherence tomography. Circulation 111(12): Brezinski ME, Tearney GJ, Weissman NJ et al (1997) Assessing atherosclerotic plaque morphology: comparison of optical coherence tomography and high frequency intravascular ultrasound. Heart 77(5): Patel NA, Stamper DL, Brezinski ME (2005) Review of the ability of optical coherence tomography to characterize plaque, including a comparison with intravascular ultrasound. Cardiovasc Intervent Radiol 28(1): Kataiwa H, Tanaka A, Kitabata H et al (2009) Head to head comparison between the conventional balloon occlusion method and the non-occlusion method for optical coherence tomography. Int J Cardiol (in press)