Multimodality direct coronary imaging with combined near-infrared spectroscopy and intravascular ultrasound: initial US experience

Epicardial Adipose Tissue Thickness Is Related to Plaque Composition in Coronary Artery Disease

(1) Background: Currently, limited data are available regarding the relationship between epicardial fat and plaque composition. The aim of this study was to assess the relationship between visceral fat surrounding the heart and the lipid core burden in patients with coronary artery diseases; (2) Methods: Overall, 331 patients undergoing coronary angiography with combined near-infrared spectroscopy and intravascular ultrasound imaging were evaluated for epicardial adipose tissue (EAT) thickness using transthoracic echocardiography. Patients were divided into thick EAT and thin EAT groups according to the median value; (3) Results: There was a positive correlation between EAT thickness and maxLCBI4mm, and maxLCBI4mm was significantly higher in the thick EAT group compared to the thin EAT group (437 vs. 293, p < 0.001). EAT thickness was an independent predictor of maxLCBI4mm ≥ 400 along with age, low-density lipoprotein-cholesterol level, acute coronary syndrome presentation, and plaque burden in a multiple linear regression model. Receiver operating characteristic curve analysis showed that EAT thickness was a predictor for maxLCBI4mm ≥ 400; (4) Conclusions: In the present study, EAT thickness is related to the lipid core burden assessed by NIRS-IVUS in patients with CAD which suggests that EAT may affect the stability of the plaques in coronary arteries.

Mechanically Rotating Intravascular Ultrasound (IVUS) Transducer: A Review

Intravascular ultrasound (IVUS) is a valuable imaging modality for the diagnosis of atherosclerosis. It provides useful clinical information, such as lumen size, vessel wall thickness, and plaque composition, by providing a cross-sectional vascular image. For several decades, IVUS has made remarkable progress in improving the accuracy of diagnosing cardiovascular disease that remains the leading cause of death globally. As the quality of IVUS images mainly depends on the performance of the IVUS transducer, various IVUS transducers have been developed. Therefore, in this review, recently developed mechanically rotating IVUS transducers, especially ones exploiting piezoelectric ceramics or single crystals, are discussed. In addition, this review addresses the history and technical challenges in the development of IVUS transducers and the prospects of next-generation IVUS transducers.

Significant decrease in lipid core burden index following balloon dilation was associated with the leakage of cholesterol crystals in a patient: a case report

BACKGROUND

Near-infrared spectroscopy (NIRS) has been used for analysis the composition of the atherosclerotic plaque in coronary arteries. However, meaning of significant decrease in max lipid core burden index at 4 mm (max LCBI_4mm) during percutaneous coronary intervention (PCI) is poorly understood.

CASE SUMMARY

A 64-year-old male with unstable angina underwent coronary angiography, which demonstrated a hazy tight culprit lesion in the mid-right coronary artery. Pre-intervention NIRS-intravascular ultrasound (NIRS-IVUS) and chemogram showed plaque with high lipid burden at the culprit lesion. Then, we used a distal protection device before PCI because of high max LCBI_4mm in the lesion. After pre-dilation with a scoring balloon, repeat NIRS-IVUS interrogation revealed an almost complete disappearance of the yellow signal and decrease in max LCBI_4mm (from 537 to 44) significantly, suggesting decrease in the lipid content of the plaque. Finally, a drug-eluting stent deployment followed by inflation of a non-compliant balloon led to an excellent result. After PCI, we detected trapped large amounts of debris on retrieval of the filter. Pathological diagnosis confirmed that trapped material was lipid-rich plaque including cholesterol crystals.

DISCUSSION

This is the first report directly demonstrated that significant decrease in max LCBI_4mm at culprit lesion should be associated with the leakage of cholesterol crystals from lipid-rich plaque during PCI in the clinical patient.

Vulnerable Plaque: A Review of Current Concepts in Pathophysiology and Imaging

Advances in our understanding of the natural history and biology of atherosclerotic vascular disease led to the concept of a vulnerable plaque (VP), which is predisposed toward more rapid progression and acute coronary events. With newer technologies, we now have at our disposal high-quality imaging studies, both invasive and noninvasive, which promise in identifying plaque characteristics that make it more vulnerable. Upcoming trials aim to evaluate the utility of imaging VP in predicting clinical events. We discuss the role of VP imaging in managing atherosclerotic vascular disease.

Comprehensive intravascular imaging of atherosclerotic plaque in vivo using optical coherence tomography and fluorescence lifetime imaging

Comprehensive imaging of both the structural and biochemical characteristics of atherosclerotic plaque is essential for the diagnosis and study of coronary artery disease because both a plaque's morphology and its biochemical composition affect the level of risk it poses. Optical coherence tomography (OCT) and fluorescence lifetime imaging (FLIm) are promising optical imaging methods for characterizing coronary artery plaques morphologically and biochemically, respectively. In this study, we present a hybrid intravascular imaging device, including a custom-built OCT/FLIm system, a hybrid optical rotary joint, and an imaging catheter, to visualize the structure and biochemical composition of the plaque in an atherosclerotic rabbit artery in vivo. Especially, the autofluorescence lifetime of the endogenous tissue molecules can be used to characterize the biochemical composition; thus no exogenous contrast agent is required. Also, the physical properties of the imaging catheter and the imaging procedures are similar to those already used clinically, facilitating rapid translation into clinical use. This new intravascular imaging catheter can open up new opportunities for clinicians and researchers to investigate and diagnose coronary artery disease by simultaneously providing tissue microstructure and biochemical composition data in vivo without the use of exogenous contrast agent.

A Novel Synchronous Micro Motor for Intravascular Ultrasound Imaging

OBJECTIVE

Intravascular ultrasound (IVUS) is an important method for evaluating lumen dimensions and guiding intervention. However, the current IVUS catheter using a proximal motor and flexible drive shaft is easily rotated at an unstable speed when it passes through along bending vessel. One approach to solve this problem is to develop a catheter driven by a distal motor.

METHODS

This paper presents a rotation device incorporating a high-frequency transducer as an attempt to facilitate this approach. A novel micro distal synchronous micro motor with 3.7 mm length and 1.2 mm outer diameter was proposed as an actuator for the IVUS catheter. A 0.5 mm × 0.5 mm Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ single crystal 1-3 composite single-element transducer was designed and manufactured. The probe is fixed to the front end of the catheter. The 45° reflector, which is opposite to the probe, was used to steer ultrasound to the tissue.

RESULTS

The results showed that the maximum torque and rotation speed of the motor were 2.79 μNm and 275 revolutions per second, respectively, at a driving current of 0.34 A. The maximum angular error was 7° at 0.13 A and 30 Hz. The center frequency and -6 dB fractional bandwidth of single element were 34 MHz and 72%, respectively. At the center frequency, the two-way insertion loss was 14 dB.

CONCLUSION

The integrated distal motor IVUS catheter, with small dimensions, a good torque, speed stability, and good ultrasound imaging performance, has tremendous potential in blood vessel imaging.

SIGNIFICANCE

The novel structure of the catheter could facilitate endoluminal sonography, reducing risks of the clinical diagnosis.

A Review of Intravascular Ultrasound-based Multimodal Intravascular Imaging: The Synergistic Approach to Characterizing Vulnerable Plaques

Catheter-based intravascular imaging modalities are being developed to visualize pathologies in coronary arteries, such as high-risk vulnerable atherosclerotic plaques known as thin-cap fibroatheroma, to guide therapeutic strategy at preventing heart attacks. Mounting evidences have shown three distinctive histopathological features-the presence of a thin fibrous cap, a lipid-rich necrotic core, and numerous infiltrating macrophages-are key markers of increased vulnerability in atherosclerotic plaques. To visualize these changes, the majority of catheter-based imaging modalities used intravascular ultrasound (IVUS) as the technical foundation and integrated emerging intravascular imaging techniques to enhance the characterization of vulnerable plaques. However, no current imaging technology is the unequivocal "gold standard" for the diagnosis of vulnerable atherosclerotic plaques. Each intravascular imaging technology possesses its own unique features that yield valuable information although encumbered by inherent limitations not seen in other modalities. In this context, the aim of this review is to discuss current scientific innovations, technical challenges, and prospective strategies in the development of IVUS-based multi-modality intravascular imaging systems aimed at assessing atherosclerotic plaque vulnerability.

Intracoronary near-infrared spectroscopy: an overview of the technology, histologic validation, and clinical applications

Intracoronary near-infrared spectroscopy (NIRS) imaging, which is now clinically available in a combined NIRS and intravascular ultrasound catheter, is a novel catheter-based imaging modality capable of identifying lipid core plaque within the coronary arteries of living patients. The present manuscript provides an overview of intracoronary NIRS imaging with a focus on several concepts essential to individuals seeking to better understand this novel imaging modality. One of the major assets of NIRS is that it has been rigorously validated against the gold standard of histopathology and has been shown to accurately identify histologically-proven fibroatheroma. Clinical studies of NIRS have demonstrated its ability to accurately identify large lipid core plaques at culprit lesions across the spectrum of acute coronary syndromes. NIRS has also been shown to detect lesions at increased risk of causing peri-procedural myocardial infarction during PCI. With regards to predicting future risk, NIRS is seemingly capable of identifying vulnerable patients at increased risk of experiencing subsequent patient-level cardiovascular events. In addition to these clinical applications of NIRS, there are several large prospective observational studies underway to determine if NIRS imaging will be able to identify vulnerable plaques at increased risk of triggering site-specific future coronary events. These studies, once completed, are anticipated to provide valuable data regarding the ability of NIRS imaging to identify plaque vulnerability.

Adjunctive intra-coronary imaging for the assessment of coronary artery disease

Atherosclerotic coronary artery disease remains a leading cause of worldwide morbidity and mortality. Invasive angiography currently remains the gold standard method of diagnosing and treating coronary disease; however, more sophisticated adjunctive interventional technologies have been developed to combat the inter and intra-observer variability frequently encountered in the assessment of lesion severity. Intravascular imaging now plays a key role in optimising percutaneous coronary interventions and provides invaluable information as part of the interventional cardiologist's diagnostic arsenal. The principles, technical aspects and uses of two modalities of intracoronary imaging, intravascular ultrasound and optical coherence tomography, are discussed. We additionally provide examples of cases where the adjunctive intracoronary imaging was superior to angiography alone in successfully identifying and treating acute coronary syndromes.

Intravascular Ultrasound Versus Optical Coherence Tomography for Coronary Artery Imaging - Apples and Oranges?

Intravascular imaging has advanced our understanding of coronary artery disease and facilitated decision-making in percutaneous coronary intervention (PCI). In particular, intravascular ultrasound (IVUS) has contributed significantly to modern PCI techniques. The recent introduction of optical coherence tomography (OCT) has further expanded this field due to its higher resolution and rapid image acquisition as compared with IVUS. Furthermore, OCT allows detailed planning of interventional strategies and optimisation before stent deployment, particularly with complex lesions. However, to date it is unclear whether OCT is superior to IVUS as an intracoronary imaging modality with limited data supporting OCT use in routine clinical practice. This review aims to compare these two intracoronary imaging techniques and the recent evidence for their use in this ever-changing field within interventional cardiology.

Fluorescence lifetime imaging and intravascular ultrasound: co-registration study using ex vivo human coronaries

Fluorescence lifetime imaging (FLIM) has demonstrated potential for robust assessment of atherosclerotic plaques biochemical composition and for complementing conventional intravascular ultrasound (IVUS), which provides information on plaque morphology. The success of such a bi-modal imaging modality depends on accurate segmentation of the IVUS images and proper angular registration between these two modalities. This paper reports a novel IVUS segmentation methodology addressing this issue. The image preprocessing consisted of denoising, using the Wiener filter, followed by image smoothing, implemented through the application of the alternating sequential filter on the edge separability metric images. Extraction of the lumen/intima and media/adventitia boundaries was achieved by tracing the gray-scale peaks over the A-lines of the IVUS preprocessed images. Cubic spline interpolation, in both cross-sectional and longitudinal directions, ensured boundary smoothness and continuity. The detection of the guide-wire artifact in both modalities is used for angular registration. Intraluminal studies were conducted in 13 ex vivo segments of human coronaries. The IVUS segmentation accuracy was assessed against independent manual tracings, providing 91.82% sensitivity and 97.55% specificity. The proposed methodology makes the bi-modal FLIM and IVUS approach feasible for comprehensive intravascular diagnosis by providing co-registered biochemical and morphological information of atherosclerotic plaques.

Optical coherence tomography--near infrared spectroscopy system and catheter for intravascular imaging

Owing to its superior resolution, intravascular optical coherence tomography (IVOCT) is a promising tool for imaging the microstructure of coronary artery walls. However, IVOCT does not identify chemicals and molecules in the tissue, which is required for a more complete understanding and accurate diagnosis of coronary disease. Here we present a dual-modality imaging system and catheter that uniquely combines IVOCT with diffuse near-infrared spectroscopy (NIRS) in a single dual-modality imaging device for simultaneous acquisition of microstructural and compositional information. As a proof-of-concept demonstration, the device has been used to visualize co-incident microstructural and spectroscopic information obtained from a diseased cadaver human coronary artery.

Detection by near-infrared spectroscopy of large lipid core plaques at culprit sites in patients with acute ST-segment elevation myocardial infarction

OBJECTIVES

This study sought to describe near-infrared spectroscopy (NIRS) findings of culprit lesions in ST-segment elevation myocardial infarction (STEMI).

BACKGROUND

Although autopsy studies demonstrate that most STEMI are caused by rupture of pre-existing lipid core plaque (LCP), it has not been possible to identify LCP in vivo. A novel intracoronary NIRS catheter has made it possible to detect LCP in patients.

METHODS

We performed NIRS within the culprit vessels of 20 patients with acute STEMI and compared the STEMI culprit findings to findings in nonculprit segments of the artery and to findings in autopsy control segments. Culprit and control segments were analyzed for the maximum lipid core burden index in a 4-mm length of artery (maxLCBI(4mm)).

RESULTS

MaxLCBI(4mm) was 5.8-fold higher in STEMI culprit segments than in 87 nonculprit segments of the STEMI culprit vessel (median [interquartile range (IQR)]: 523 [445 to 821] vs. 90 [6 to 265]; p < 0.001) and 87-fold higher than in 279 coronary autopsy segments free of large LCP by histology (median [IQR]: 523 [445 to 821] vs. 6 [0 to 88]; p < 0.001).Within the STEMI culprit artery, NIRS accurately distinguished culprit from nonculprit segments (receiver-operating characteristic analysis area under the curve = 0.90). A threshold of maxLCBI(4mm) >400 distinguished STEMI culprit segments from specimens free of large LCP by histology (sensitivity: 85%, specificity: 98%).

CONCLUSIONS

The present study has demonstrated in vivo that a maxLCBI(4mm) >400, as detected by NIRS, is a signature of plaques causing STEMI.

Spectroscopic Imaging of Deep Tissue through Photoacoustic Detection of Molecular Vibration

The quantized vibration of chemical bonds provides a way of imaging target molecules in a complex tissue environment. Photoacoustic detection of harmonic vibrational transitions provides an approach to visualize tissue content beyond the ballistic photon regime. This method involves pulsed laser excitation of overtone transitions in target molecules inside a tissue. Fast relaxation of the vibrational energy into heat results in a local temperature rise on the order of mK and a subsequent generation of acoustic waves detectable with an ultrasonic transducer. In this perspective, we review recent advances that demonstrate the advantages of vibration-based photoacoustic imaging and illustrate its potential in diagnosing cardiovascular plaques. An outlook into future development of vibrational photoacoustic endoscopy and tomography is provided.