Purpose
To compare the diagnostic performance of Intravascular Ultrasound (IVUS) and Optical Coherence Tomography (OCT) imaging in the matched segments of peripheral vessels in patients with suspected peripheral vascular disease.
Methods
The SCAN study was a prospective, non-inferiority clinical study of matched IVUS and OCT images collected along defined segments of peripheral vessels from twelve subjects (mean age 68 ? 10.3 years; 10 men) displaying symptoms of vascular disease. Luminal diameters were measured by both imaging systems at the distal, middle, and proximal points of the defined segments. Three blinded interventional radiologists evaluated the quality of both imaging modalities in identifying layered structures (3-point grading), plaque (5-point grading), calcification (5-point grading), stent structure (3-point grading), and artifacts. (3-point grading) from 240 randomly ordered images. Mean grading scores and luminal diameters were calculated and analyzed with Student’s t-Test and Mann-Whitney-Wilcoxon testing. Intrareader reproducibility was calculated by Intraclass Correlation (ICC) analysis.
Results
The mean scoring of plaque, calcification, and vascular stent struts by the three readers was significant better in terms of image quality for OCT than IVUS (p<0.001, p=0.001, p=0.004, respectively). The mean scores of vessel wall component visibility and artifacts generated by the two imaging systems were not significantly different (p=0.19, p=0.07, respectively). Mean vessel luminal diameter and area at three specific locations within the vessels were not significantly different between the two imaging modalities. No patient injury, adverse effect or device malfunction were noted during the study.
Conclusion
OCT imaging is a safe and effective method of examining peripheral vessels in order to perform diagnostic assessment of peripheral vessels and provide information necessary for the treatment strategy of peripheral artery disease.
Intravascular imaging has been used for many years in visualization and characterization of coronary vessel morphology and presence of atherosclerotic plaque, resulting in improved success in treatments and clinical outcome due to better risk stratification [1,2]. For example, the evaluation of stent position and appropriate sizing of coronary stents by OCT imaging can determine stent malposition so that further dilation can be accomplished to improve stent placement at the time of the procedure [3].
Drawing on the utility in coronary vessels, intravascular imaging has become much more frequently utilized as an adjunct to angiography in the treatment of Peripheral Artery Disease (PAD).The ability to visualize internal vessel architecture provides clinicians with information useful in the evaluation of stenosis, dissection and plaque morphology. Intravascular imaging can therefore assist in the development or modification of a treatment strategies [4]. Such imaging has also shown utility in post-treatment assessments, which can result in increased treatment success and a reduction in patient morbidity [5,6].
The two primary modalities of such imaging are Intravascular Ultrasound (IVUS) and Optical Coherence Tomography (OCT). As the name denotes, IVUS interprets high-frequency sound waves that rebound off vessel walls and are collected by a processing system. The intensity of the sound waves varies depending on the tissue encountered and the operating system processes the signals in order to create a cross-sectional image [7]. IVUS can be used to measure plaque extent, morphology and distribution, but it has low spatial resolution (150 µm) and calcium deposits in the vessel walls can reduce penetration of the sound waves [8,9]. In contrast, OCT imaging measures the intensity reflected near-infrared light that is captured by a system to develop images of tissue and structures [10]. OCT images have higher resolution (10 µm) and faster imaging acquisition than IVUS [11], but such imaging requires management of blood flow that can interfere with light transmission [12].
IVUS and OCT imaging in peripheral vessels has been noted to have comparable utilities in peripheral vessels to their use in coronary arteries through assessing vessel characteristics and morphology, such as vessel and lumen diameter, area of stenosis, and plaque location and extent [13,14] (Figure 1). By utilizing intravascular visualization, the physician is able to diagnosis the patient’s specific vascular condition and develops a treatment strategy to a level of refinement not possible with angiography [15]. The purpose of this study was to compare images collected by IVUS and OCT imaging in the same segment of peripheral vessels with respect to image quality, tissue characterization, and lumen dimensions as supporting technologies for diagnosis of the patient’s condition and the development of treatment strategies for peripheral artery disease.
Figure 1: OCT imaging (left) and IVUS imaging (right) of peripheral vessel morphology. A. Layered structure of the components of the vessel wall. B. Presentation of plaque within the lumen of the vessel.
No. of patients |
12 |
Mean age, years (range) |
68 (55 - 87) |
Sex |
Male 10 (83%). Female 2 (17%) |
Race |
Caucasian 92%. African-American (8%) |
Mean weight, kg (range) |
82 (69 - 92) |
Mean height, cm (range) |
176.8 (167.6 - 187.9) |
Leg of the vessel accessed |
Left 9 (75%). Right (25%) |
Vessel imaged |
SFA (64%) Popliteal (36%) |
Mean length of target segment of vessel, cm (range) |
24 (10 - 60) |
Number of images containing a specific vessel characteristic to be scored |
24 |
Statistical analyses were carried out using Statview software (SAS Institute, Cary, NC). A p value < 0.05 was considered statistically significant. Matched Pairs t-Test were performed to compare means and on paired samples to compare procedural data and complications associated with the imaging techniques. The Mann-Whitney-Wilcoxon test was applied for statistical comparison of the scores of all three readers. A two-way Intraclass Correlation (ICC) was calculated to assess intra-reader reproducibility.
Incidence and severity of procedure-related and device-related adverse events (e.g., vessel spasm, thrombosis, distal embolism, etc.,) were evaluated following each scan and documented over the course of the study.
Vessel Characteristic |
Mean score for IVUS images |
Mean score for OCT images |
Student’s t-Test |
Mann-Whitney-Wilcoxon test |
Layered structure |
1.61 |
1.49 |
p = 0.19 |
z = 0.82 |
Non-layered structure |
2.70 |
1.82 |
p< 0.001 |
z= 11.04 |
Calcification |
2.45 |
2.11 |
p = 0.001 |
z = 2.80 |
Stent structure |
1.79 |
1.43 |
p = 0.004 |
z = 2.67 |
Artifacts |
1.87 |
1.79 |
p= 0.07 |
z= - 1.52 |
Table 2: Mean ranking of the image quality of layered structure, non-layered structure, calcification, stent structure, and artifacts as rated by three readers of matched images captured by OCT and IVUS systems.
Scoring: Layered structure (1- clear differentiation of vessel wall layers, 2- differentiation of 3 wall layers, 3-differentiation of 2 wall layers, 4- no differentiation visible); Non-layered structure (1- excellent histology-like image quality to 5- unacceptably poor image quality); Calcification (1- excellent histology-like image quality to 5- unacceptably poor image quality);Stent structure (1 excellent image, 2- acceptable image, 3- unacceptably poor image); and Artifacts (1-none, 2- tolerable/not limiting, 3-is intense and limits image quality)
Reader |
Layered Structure |
Non-Layered Structure |
Calcification |
Stent Structure |
Artifacts |
1
ICC intrareader |
IVUS OCT 1.58 1.12 p = 0.002 0.82 0.91 |
IVUS OCT 2.97 2.08 p <0.001 0.890.91 |
IVUS OCT 2.28 2.05 p < 0.001 0.77 0.83 |
IVUS OCT 2.00 1.48 p < 0.001 0.82 0.93 |
IVUS OCT 2.15 1.68 p < 0.001 0.85 0.81 |
2
ICC intrareader |
1.42 1.04 p = 0.02 0.70 0.83 |
2.55 1.54 p < 0.001 0.73 0.81 |
2.15 1.60 p < 0.001 0.91 0.85 |
1.81 1.14 p < 0.001 0.84 0.88 |
1.73 1.51 p < 0.001 0.92 0.83 |
3
ICC intrareader |
1.83 2.29 p = 0.005 0.840.75 |
2.58 1.84 p < 0.001 0.89 0.77 |
2.95 2.68 p = 0.19 0.92 0.87 |
1.52 1.67 p = 0.52 0.83 0.86 |
1.22 2.33 p < 0.001 0.92 0.81 |
Table 3: Mean ranking of the image quality of layered structure, non-layered structure, calcification, stent structure, trough after treatment, and artifacts as rated by three readers of matched images captured by OCT and IVUS systems.
Scoring: Layered structure (1- clear differentiation of vessel wall layers, 2- differentiation of 3 wall layers, 3-differentiation of 2 wall layers, 4- no differentiation visible); Non-layered structure (1- excellent histology-like image quality to 5- unacceptably poor image quality); Calcification (1- excellent histology-like image quality to 5- unacceptably poor image quality);Stent structure (1 excellent image, 2- acceptable image, 3- unacceptably poor image); and Artifacts (1-none, 2- tolerable/not limiting, 3-is intense and limits image quality)
Proximal Location |
Middle Location |
Distal Location |
||||||||
Patient |
Imaging Modality |
Longest Diameter (mm) |
Shortest Diameter (mm) |
Luminal Area from Longest Diameter (sq mm) |
Longest Diameter (mm) |
Shortest Diameter (mm) |
Luminal Area from Longest Diameter (sq mm) |
Longest Diameter (mm) |
Shortest Diameter (mm) |
Luminal Area from Longest Diameter (sq mm) |
P1 |
IVUS |
5.4 |
4.3 |
22.9 |
5.1 |
4.6 |
20.43 |
3.5 |
3 |
9.62 |
OCT |
6.1 |
3.9 |
29.22 |
5.7 |
4.2 |
25.52 |
3.8 |
3.3 |
11.34 |
|
P2 |
IVUS |
4.3 |
4 |
14.52 |
3.8 |
3.2 |
11.34 |
2.9 |
2.5 |
6.6 |
OCT |
3.9 |
3.3 |
11.95 |
4.2 |
3 |
13.85 |
3.2 |
3 |
8.04 |
|
P3 |
IVUS |
3.9 |
3 |
11.95 |
4.4 |
4 |
15.2 |
3.1 |
2.6 |
7.54 |
OCT |
4.2 |
2.9 |
13.85 |
4.6 |
4.3 |
16.62 |
3.2 |
2.7 |
8.04 |
|
P4 |
IVUS |
6.4 |
5.9 |
32.17 |
5.2 |
4.7 |
21.24 |
3.4 |
3.3 |
9.08 |
OCT |
5.7 |
5.3 |
25.52 |
4.8 |
4.4 |
18.09 |
3.1 |
2.9 |
7.55 |
|
P5 |
IVUS |
6.7 |
5.8 |
35.26 |
5.9 |
5.1 |
27.34 |
5.9 |
5.4 |
27.34 |
OCT |
5.7 |
5 |
25.52 |
5.5 |
4.8 |
23.76 |
5.5 |
5.1 |
23.76 |
|
P6 |
IVUS |
4.8 |
4.1 |
18.09 |
3.8 |
3.1 |
11.34 |
3.3 |
2.8 |
8.55 |
OCT |
5.4 |
4.1 |
22.9 |
3.6 |
2.8 |
10.18 |
3.5 |
3 |
9.62 |
|
P7 |
IVUS |
5.3 |
4.3 |
22.06 |
4.6 |
4 |
16.62 |
3.2 |
2.8 |
8.04 |
OCT |
4.6 |
4 |
16.62 |
4.2 |
3.5 |
13.85 |
3 |
2.6 |
7.06 |
|
P8 |
IVUS |
5.3 |
4.3 |
22.06 |
5.4 |
4.8 |
22.9 |
4.6 |
4.2 |
16.62 |
OCT |
5.6 |
4.7 |
24.63 |
5.1 |
4.3 |
20.43 |
4.9 |
4.3 |
18.86 |
|
S1 |
IVUS |
3.5 |
3 |
9.62 |
3.6 |
2.5 |
10.18 |
3 |
2.3 |
7.07 |
OCT |
3.8 |
3.2 |
11.34 |
3.8 |
2.6 |
11.34 |
3.1 |
2.4 |
7.55 |
|
S2 |
IVUS |
2.9 |
2 |
6.6 |
2.2 |
1.8 |
3.8 |
2.3 |
2.1 |
4.15 |
OCT |
2.8 |
2.5 |
6.16 |
2.4 |
2 |
4.52 |
3.2 |
2.4 |
8.04 |
|
S3 |
IVUS |
3.7 |
2.9 |
10.75 |
3.9 |
3.4 |
11.94 |
3.3 |
2.7 |
8.55 |
OCT |
4.1 |
2.4 |
13.2 |
3.4 |
2.6 |
9.08 |
3 |
2.5 |
7.07 |
|
S4 |
IVUS |
4.6 |
4.2 |
16.62 |
3.9 |
3.4 |
11.94 |
3.1 |
2.8 |
7.55 |
OCT |
4.3 |
3.9 |
14.52 |
3.7 |
3.1 |
10.75 |
2.8 |
2.5 |
6.16 |
|
MEANS |
IVUS |
4.7 |
3.9 |
18.55 |
4.3 |
3.7 |
15.36 |
3.5 |
3 |
10.06 |
OCT |
4.7 |
3.8 |
17.28 |
4.2 |
3.4 |
14.83 |
3.5 |
3 |
10.26 |
|
p = 0.80 |
p = 0.10 |
p = 0.39 |
p = 0.54 |
p = 0.02 |
p = 0.52 |
p = 0.60 |
p = 0.96 |
p = 0.74 |
Table 4: The longest and shortest luminal diameter of vessels at the distal, middle, and proximal portions of the target segments of vessels and the resultant luminal area as measured by the Pantheris OCT or Visions PV IVUS systems.
This is the first study comparing the quality of IVUS and OCT images in peripheral vessels in patients in the United States. The quality of the two modalities were comparable for differentiation of vessel wall layers and the amount of artifact present in the images, while OCT imagin was ranked as significantly better for imaging luminal plaque, calcium, and foreign body structures, such as stent struts. Even though some of the vessel characteristics were significantly better visualized by OCT than with IVUS, this study was designed to determine the characteristics of both imaging modalities to assist physicians in the diagnosis of and development of treatment strategy for patients with peripheral arterial disease. OCT imaging was comparable to imaging by IVUS technology for visualizing layered structures and having insufficient interference from artifacts to obscure the field of view, both of which provide important information to the physician during a procedure. While the OCT scores for identifying plaque, calcium deposition in the wall, and indwelling devices (vascular stents) were significantly higher than those of the IVUS catheter, the scores given to the IVUS images were within the ranking levels that equate to the image quality of IVUS as “very good” and provided sufficiently clear imaging to allow the physician to complete diagnostic review and treatment strategy for PAD.
Intravascular imaging to support diagnosis and treatment of peripheral artery disease is becoming an important factor in new and evolving endovascular interventions. Use of such imaging can help form the treatment strategy, size the vessel so that the appropriate diameter of balloons or stents being placed is chosen, and guide and direct treatments such as angioplasty and atherectomy to minimize vessel wall injury [6,16-20]. Intravascular imaging also permits assessment of tissue in the region of the procedure in order to determine whether further treatment is necessary to address regions with incomplete treatment or injury resulting from the treatment [19,21,22].
An important variable in the outcome of revascularization procedures is the type and extent of calcium in coronary and peripheral lesions since the incidence of revascularization and treatment success decreases as calcium burden in plaque increases [23-25]. Intravascular imaging to assess calcium in peripheral lesions provides information on the characteristics of calcium present in peripheral lesions as well as burden within the tissue [6,26-29]. Use of either IVUS or OCT imaging to diagnose and guide treatment of calcified lesions in peripheral vessels has been associated with improved treatment outcomes since they either determine the appropriate path around such deposits or the appropriate treatment method to be used. In this study, diagnosis of calcium within the vessel walls was ranked as close to histology-like for both OCT and IVUS imaging, which would provide the interventionalist with sufficient information to develop treatment options [30]. In this study, both imaging modalities identified the location and extent of calcium in the vessel at levels of clarity that were clinically beneficial.
OCT imaging has a long history in coronary vessels in the assessment of vessel injury following treatment [31-33] and is used in peripheral vessels for not only diagnosis of conditions in the vessels [34] but also has been shown to be capable of characterizing different types of atherosclerotic plaque [14]. In coronary vessel disease, OCT imaging has caused the change in treatment strategy and assessment of the treatment. In the ILUMIEN I study, the information gained from OCT imaging prior to treatment changed the pre-imaging plan in 55% of patients in up to 80% of the cases, primarily in selection of vascular stent length, diameter, and number used [35]. After stent implantation in coronary vessels, OCT imaging is used to assess the stent position and dilatation, which, when corrected, results in better clinical outcomes [35,36].
OCT imaging in peripheral vessels has been integrated into clinical practice since 2012, with the early results demonstrating assessment of calcium deposition and injury to the vessel wall from previous treatments [30]. With increased use of intravascular OCT imaging, interventionalists are able to review the vessel lumen, wall components, and abnormal physiology in peripheral vessels preoperatively, [11,13-15,29,34] which are important conditions to identify in making a diagnosis and choosing procedural options. Intravascular OCT imaging of peripheral vessels containing stents has allowed interventionalists to determine the extent of neointimal tissue growth resulting in in-stent restenosis [20]. And the extent of stent revascularization in peripheral vessels following an interventional procedure [20,22,37,38].
OCT-guided atherectomy has clinical benefits of tissue excision with minimal injury to healthy tissue, reduction in the use of contrast agents or radiation, and focused treatment following the identification of plaque distribution and morphology [20]. Schwindt et al., [6] noted that OCT-guided directional atherectomy resulted in 62% of lesions being removed with no disruption or contact with adventitia and 82% of lesions having less than 1% adventitia in excised tissue, which may have contributed to the 92% freedom from target lesion revascularization rate noted at six months post-procedure. Non-radiation imaging such as OCT provides physicians as well as patients with an option of visualization of intravascular conditions with minimal or no contrast or radiation. Contrast use in patients with chronic kidney disease carries risk but use of OCT imaging can be used to measure lesions in lower extremities without use of iodinated contrast agents [39]. OCT imaging provides information on the diameter of peripheral lesions that can direct the physician to choose the correct size of vascular stent or balloon angioplasty, which is associated with longer periods of patency [40]. In contrast, atherectomy relying solely on angiographic guidance can result in suboptimal volumes of plaque excised and injury to the adventitia [19], resulting in restenosis within a shorter period of time than desired [41,42].
In a similar manner, IVUS imaging prior to and following vascular procedures have been reported to differentiate plaque morphology, assist in stent and balloon sizing, and identification of procedure-related injuries, such as dissection [4,43,44], which result in improved clinical outcomes. IVUS-directed percutaneous coronary interventions has been demonstrated to have lower incidence of stent thrombosis [45], while use of IVUS in peripheral vessels can monitor treatment efficacy in real-time, which is associated with lower target lesion revascularization rates up to one year post-procedure [42,5].
A limitation to this study is the number of subjects enrolled, which may not have provided the breath of physiological and pathological presentations associated with peripheral arterial disease. However, the twelve subjects included in this study did have varying levels of vascular disease, which is more relevant to clinical procedures than previous imaging studies carried out on healthy peripheral vessels.
From the results of this study, OCT and IVUS imaging are safe and effective methods of examining peripheral vessels in order to diagnose and maximize the clinical benefit of treatment of peripheral artery disease. OCT imaging of peripheral vessels in vivo was comparable to IVUS imaging in the detection of layered structures, treatment zones, and artifacts. OCT was found to be superior to IVUS imaging in the differentiation of plaque, the presence of calcium in the vessel wall, and the presence of vascular stents. Use of intravascular imaging prior to a procedure can direct treatment strategy due to its high resolution of vascular tissue and anomalies in the vessel wall and measuring of lumens to direct choice in appropriate stent sizes. Use of intravascular imaging after an intervention can guide the need for addition intervention such as stent placement or further expansion of poorly implanted stents. Both IVUS and OCT imaging have moved out of the research stage of clinical procedures and into daily use in order to increase the efficacy of vascular interventional procedures without increasing risk.
Citation: Pavillard E (2019) A Post-market, Multi-vessel Evaluation of the Imaging of Peripheral Arteries for Diagnostic Purposes Comparing Optical Coherence Tomography and Intravascular Ultrasound Imaging (SCAN). J Surg Curr Trend Innov S1: 003.
Copyright: © 2019 Edward Pavillard, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.