Optimal flushing agents for integrated optical and acoustic imaging systems

Comparison of the effects of contrast medium and low-molecular-weight dextran on coronary optical coherence tomographic imaging in relatively complex coronary lesions

Background

Optical coherence tomography (OCT) has gained increasing popularity in coronary artery intervention due to its high resolution and excellent tissue correlation as a novel intravascular imaging modality. However, the current use of OCT requires contrast agent injection for imaging, and excessive use of contrast agents may adversely affect renal function, exacerbate cardiac burden, and even lead to contrast agent-induced nephropathy and heart failure. In recent years, several researchers have proposed the use of low molecular weight dextran (LMWD) as a substitute for contrast agents in OCT imaging because of its low toxicity, low cost, and wide availability. However, the inclusion of lesions in these studies is relatively simple, and the image quality criteria remain to be optimized.

Methods

This study included 26 patients with coronary artery disease who were scheduled for OCT imaging in a real-world clinical practice involving various complex lesions. All patients underwent two OCT examinations at the same vascular site, one each using contrast agent and LMWD. Both contrast media and LMWDs were infused by an autoinjector. The primary endpoint of the study was the average image quality score. Secondary endpoints included clear image length, clear image segments, minimum lumen area, average lumen area, and contrast-induced nephropathy, among others.

Results

In terms of image clarity, the average image quality score was similar when comparing contrast media with LMWD (3.912 ± 0.175 vs. 3.769 ± 0.392, P = 0.071). The lengths of the clear images and the segments of the clear images were also similar between the two groups (50.97 ± 16.25 mm vs. 49.12 ± 18.15 mm, P = 0.110; 255.5 ± 81.29 vs. 250.5 ± 89.83, P = 0.095). Additionally, strong correlations were noted between the two flushing solutions regarding the minimum lumen area and mean lumen area. During their hospital stay, none of the patient exhibited deterioration in renal function, and no patient experienced any major adverse cardiovascular events.

Conclusions

The quality of coronary artery OCT imaging using LMWD may be comparable to that achieved with traditional contrast agents, even in real-world clinical practice involving various complex lesions. For high-risk patients, LMWD may serve as an excellent substitute for contrast agents in OCT examinations.

Evaluation of Blood Induced Influence for High-Definition Intravascular Ultrasound (HD-IVUS)

High-definition intravascular ultrasound (HD-IVUS) utilizing more than 80 MHz frequency to assess atherosclerotic plaque, can theoretically achieve an axial resolution of less than [Formula: see text]. However, the blood is a high-attenuation source at high frequency, which would affect the imaging quality. There has been no research evaluating the blood-induced influence on HD-IVUS imaging. And whether a temporary removal of blood is needed for HD-IVUS is unknown. In this study, an ultrahigh-frequency (100 MHz) ultrasound transducer was developed to evaluate the blood-induced attenuation for HD-IVUS imaging. A series of tungsten-wire phantom images in saline and blood at varying hematocrits were obtained. The images showed that blood did influence the ultrahigh-frequency imaging quality greatly. The signal-to-noise ratio (SNR) decrease by 71.7% in porcine whole blood compared to that in saline at the same depth of 2.3 mm. Moreover, the potential flushing schemes for HD-IVUS were studied in varying hematocrits. Three flushing agents commonly used in intravascular optical coherence tomography (IV-OCT) were investigated, including iohexol, mannitol, and dextran 5% and saline as the control group. The attenuation of blood in varying hematocrits/flushing agents was measured from 90 to 110 MHz. The result indicated dextran 5% was a suitable flushing agent for HD-IVUS due to its less signal attenuation compared to others.

Multimodal intravascular imaging technology for characterization of atherosclerosis

Early detection of vulnerable plaques is the critical step in the prevention of acute coronary events. Morphology, composition, and mechanical property of a coronary artery have been demonstrated to be the key characteristics for the identification of vulnerable plaques. Several intravascular multimodal imaging technologies providing co-registered simultaneous images have been developed and applied in clinical studies to improve the characterization of atherosclerosis. In this paper, the authors review the present system and probe designs of representative intravascular multimodal techniques. In addition, the scientific innovations, potential limitations, and future directions of these technologies are also discussed.

Measurement of tissue optical properties in the context of tissue optical clearing

Nowadays, dynamically developing optical (photonic) technologies play an ever-increasing role in medicine. Their adequate and effective implementation in diagnostics, surgery, and therapy needs reliable data on optical properties of human tissues, including skin. This paper presents an overview of recent results on the measurements and control of tissue optical properties. The issues reported comprise a brief review of optical properties of biological tissues and efficacy of optical clearing (OC) method in application to monitoring of diabetic complications and visualization of blood vessels and microcirculation using a number of optical imaging technologies, including spectroscopic, optical coherence tomography, and polarization- and speckle-based ones. Molecular modeling of immersion OC of skin and specific technique of OC of adipose tissue by its heating and photodynamic treatment are also discussed.

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.

Integrated intravascular ultrasound and optical coherence tomography technology: a promising tool to identify vulnerable plaques [INVITED PAPER]

Heart attack is mainly caused by the rupture of a vulnerable plaque. IVUS-OCT is a novel medical imaging modality that provides opportunities for accurate assessment of vulnerable plaques in vivo in patients. IVUS provides deep penetration to image the whole necrotic core while OCT enables accurate measurement of the fibrous cap of a plaque owing to its high resolution. In this paper, the authors describe the fundamentals, the technical designs and the applications of IVUS-OCT technology. Results from cadaver specimens are summarized, which indicated the complementary nature of OCT and IVUS for assessment of vulnerable plaques, plaque composition, and stent-tissue interactions. Furthermore, previously reported in vivo animal experiments are reviewed to assess the clinical adaptability of IVUS-OCT. Future directions for this technology are also discussed in this review.

Enhancement of OCT imaging by blood optical clearing in vessels – A feasibility study

The results of a feasibility study of the application of PEG-300 and fructose as two independent optical clearing agents for the reduction of light scattering in biological tissues are presented.

An OCT system operating at 1300 nm was used to study optical clearing effects. In

The intradermal injection of fructose in combination with the intravenous injection of PEG-300 led to a rapid optical clearing effect. In the experiments on mice

The experiments on mice have clearly demonstrated that intradermal and intravenous injections of optical clearing agents enhanced light transport through the skin and blood vessels.