Optical coherence tomography (1, 2) (OCT) and intravascular ultrasound (3) (IVUS) are increasingly used in clinical practice (4). OCT utilizes broadband near-infrared light (wavelengths typically in the vicinity of 1,310 nm) and low-coherence interferometry to detect tissue reflections, achieving high axial resolution (10–20 μm) for detailed visualization of vascular endothelium and plaque microstructures, though limited by light scattering to penetration depths <2 mm. Conversely, IVUS utilizes high-frequency ultrasound (typically 20–40 MHz) to penetrate deeper tissue (5–8 mm) by detecting acoustic impedance variations at tissue interfaces, but exhibits lower resolution (axial: 80–150 μm) (5) Multiple randomized controlled studies (6, 7) have confirmed that percutaneous coronary interventions (PCI) guided by IVUS or OCT optimization achieved better clinical outcomes. The updated 2024 European Society of Cardiology (ESC) Guidelines for the management of chronic coronary syndromes affirm the immediate and long-term benefits of IVI-guided PCI. They strongly recommend (Class I, Level A) the use of intravascular ultrasound (IVUS) or optical coherence tomography (OCT) for PCI in patients with complex coronary anatomy, particularly those with left main disease, true bifurcations, and long lesions (8).

However, each technology has its limitations; IVUS offers deeper penetration, enabling visualization of the entire vessel wall and detection of deep calcification, but is hampered by lower resolution, which impedes reliable differentiation between superficial and deep calcification (9). Conversely, OCT provides higher resolution (10), but its limited penetration depth may cause the outer margin of calcified plaques to be mistaken for lipid plaques, potentially leading to suboptimal selection of modification devices and under-expanded stents (11). Therefore, combining both techniques enables multimodal imaging that delivers more comprehensive histological and morphological information about vessels (12, 13). We evaluated the clinical application of the hybrid IVUS-OCT intracoronary imaging system by comparing with single mode of OCT and IVUS, aiming to provide a reference for clinical application and promotion.

The 2024 ESC guidelines' Class Ia recommendation for intravascular imaging (IVI) in complex percutaneous coronary intervention (PCI) underscores its established role in optimizing outcomes (8, 24). However, the inherent limitations of single-modality intravascular ultrasound (IVUS) and optical coherence tomography (OCT)—specifically, IVUS's lower resolution impeding detailed superficial characterization and OCT's limited penetration depth—restrict their capacity for comprehensive lesion assessment (2, 25–27). To bridge this gap, we evaluated a novel hybrid IVUS-OCT intracoronary imaging system designed to synergistically combine these complementary modalities. Our findings demonstrate that this integrated approach significantly outperforms either single-modality IVUS or OCT alone in assessing coronary atherosclerotic plaque characteristics and immediate post-stent outcomes.

In the plaque characteristics analysis, OCT alone identified 21 lipid plaques, 16 calcified plaques, and 3 possible TCFAs, with a maximal calcified plaque arc identification accuracy of 68.75%. IVUS alone identified 15 lipid plaques and 20 calcified plaques, with a maximal calcified plaque arc identification accuracy of 85%. Due to the limited penetration, OCT is unable to visualize deeper plaque components especially beyond lipid plaque or a layer of macrophages. In this study, OCT missed deep calcified plaques and failed to confirm TCFAs due to its inability to characterize plaque components beyond the lipid plaque and macrophages and to measure the size of lipid plaques. There was 3 of the possible TCFA detected by OCT alone, however there was one non-TCFA by hybrid imaging, because there were thin fiber tissue beyond the macrophages. Furthermore, in assessing the maximal calcified plaque arc, OCT is less accurate than IVUS. IVUS defines lipid plaques by visually observing the strength of the plaque echo compared to the echo of the external elastic membrane. The echo strength is influenced not only by tissue density but also by the relative position and arc of the ultrasound catheter to the plaque. Consequently, IVUS can easily confuse lipid plaques with fibrous plaques and may overlook smaller lipid plaques. However, for calcified plaques, IVUS shows good results and can provide accurate calcification information. Moreover, IVUS can evaluate plaque burden and vascular remodeling index, effectively guiding the selection of surgical strategies (13). Although IVUS performs better in identifying calcified plaques compared to OCT, it cannot measure the size of calcified plaques. IVUS also struggles to measure fibrous cap thickness because the lower resolution and cannot assess TCFA. Since plaque characteristics involve numerous parameters, evaluating them comprehensively with a single-modality is challenging (28). This limitation affects the ability to assess the effects of pharmacological interventions on plaques (29), thereby impacting the development of coronary intervention strategies. The hybrid IVUS-OCT imaging system offers dual-modality imaging that compensate for the limitations of each other, allowing for the simultaneous capture of images of plaque characteristics and function, enabling more accurate assessment of plaque characteristics and better guiding clinical decisions.

Regarding immediate post-stent evaluation, our results confirmed that OCT surpassed IVUS in clearly identifying stents, detecting incomplete stent apposition, and identifying tissue protrusion (P < 0.05), aligning with previous studies (30). This is attributed to the higher resolution of OCT, enabling it to clearly visualize subtle structural changes surrounding the stent. Nonetheless, OCT and IVUS alone have limitations in immediate post-stent evaluation. The hybrid IVUS-OCT imaging demonstrated excellent performance in this regard, clearly displaying stents and detecting all cases of incomplete stent apposition, tissue protrusion, and stent edge dissection. Clinically, the hybrid IVUS-OCT imaging system provides detailed and accurate immediate post-stent evaluations, helping to avoid the need for repeat procedures and reducing postoperative complications. OCT offers significant advantages for post-stent evaluation, but for patients with suboptimal OCT imaging, IVUS can serve as a complementary analysis tool, reducing repetitive procedures and excessive contrast agent use, thereby decreasing the incidence of cardiovascular adverse events. IVUS also helps to guide stent size selection by providing the measurement of external elastic membrane (EEM) (31–33). The plaque burden can be accurately measured by the hybrid IVUS-OCT imaging system.

The hybrid IVUS-OCT imaging system has been applied clinically recently, and there are few reports regarding its clinical efficacy. While previous studies have compared the clinical effects of OCT and IVUS separately, they did not scan images simultaneously, which means they could not ensure that OCT and IVUS images were from the same frame. In this study, both plaque characteristic analysis and post-stent evaluation showed that the hybrid IVUS-OCT imaging system performed well in clinical guidance, realizing the benefits of complementary imaging (34). It enables preoperative strategy selection or postoperative outcome evaluation leveraging the other modality if one underperforms, thereby minimizing additional procedures and excessive contrast agent administration. Additionally, it alleviates the dilemma of selecting the appropriate coronary intravascular imaging modality, especially during the interventional treatment of complex coronary lesions (35). It is important to note that since OCT imaging requires contrast agent flushing, careful consideration is necessary for patients with left main lesions, severe heart failure, or renal dysfunction (36). In these cases, the hybrid system can be operated in IVUS mode without requiring contrast agent flushing.

In this study, no adverse reactions related to coronary intravascular imaging were observed in any patients. Several limitations of this study warrant consideration. First, the single-center design and relatively small sample size limit the generalizability of the findings. Second, the evaluation of plaque characteristics and post-stent outcomes relied solely on intravascular imaging modalities lacking histological gold standard validation.Third, the lack of long-term clinical follow-up data precludes assessment of whether the superior lesion characterization and stent assessment provided by the hybrid system translates to improved clinical outcomes (e.g., reduced major adverse cardiovascular events, target lesion revascularization) compared to single-modality guidance. Finally, while image analysis was performed offline by two independent researchers with adjudication by a third in case of disagreement, inherent subjectivity in interpreting intravascular images, especially for subtle findings, remains a potential source of bias.

This study demonstrates the advantages of the hybrid IVUS-OCT intravascular imaging system and its excellent clinical guidance potential. Future studies should be conducted with larger sample sizes, multi-center involvement, and randomized designs to obtain more valuable clinical data on the clinical application of the hybrid IVUS-OCT imaging system.