Interference-free Detection of Lipid-laden Atherosclerotic Plaques by 3D Co-registration of Frequency-Domain Differential Photoacoustic and Ultrasound Radar Imaging

Advances of nanoparticle-mediated diagnostic and theranostic strategies for atherosclerosis

Atherosclerotic plaque remains the primary cause of morbidity and mortality worldwide. Accurate assessment of the degree of atherosclerotic plaque is critical for predicting the risk of atherosclerotic plaque and monitoring the results after intervention. Compared with traditional technology, the imaging technologies of nanoparticles have distinct advantages and great development prospects in the identification and characterization of vulnerable atherosclerotic plaque. Here, we systematically summarize the latest advances of targeted nanoparticle approaches in the diagnosis of atherosclerotic plaque, including multimodal imaging, fluorescence imaging, photoacoustic imaging, exosome diagnosis, and highlighted the theranostic progress as a new therapeutic strategy. Finally, we discuss the major challenges that need to be addressed for future development and clinical transformation.

Multispectral photoacoustic holography of elastomers from a bright background

Photoacoustic imaging of elastomers has important biomedical value. However, a bright background, e.g., blood vessels in living tissue, brings a challenge for photoacoustic elastography. In this study, we predicted that the spectrum of photoacoustic signals from elastomers with high elasticity could appear as narrow peaks at the eigen-frequencies of elastomers, but the signals from a bright background, e.g., blood vessel, show flat broadband spectrum for their low-quality factor. Even when the two kinds of signals are mixed together, the signals from elastomers can be identified from the spectrum since they present as convex narrow peaks on a wide base. Based on this factor, we propose a multispectral photoacoustic holography to realize selective imaging of tiny elastomers. This method recovers the image only using several frequency components in photoacoustic signals, instead of the whole-band signal. Since these narrow peaks in the spectrum correspond to the eigen-vibration of elastomers, the proposed method can highlight the elastomers with high elasticity from a bright background with low elasticity. The method was validated by experiments. This study might be helpful to localize elastic anomalous areas in the tissue, such as calcification in the vascular network, microcalcification in a tumor, and implants.

Effects of lipid composition on photothermal optical coherence tomography signals

SIGNIFICANCE

Photothermal optical coherence tomography (PT-OCT) has the promise to offer structural images coregistered with chemical composition information, which can offer a significant impact in early detection of diseases such as atherosclerosis.

AIM

We take the first step in understanding the relation between PT-OCT signals and the endogenous tissue composition by considering the interplay between the opto-thermo-physical properties of tissue as a function of its lipid composition and the ensuing effects on the PT-OCT signals.

APPROACH

Multiparameter theoretical estimates for PT-OCT signal as a function of composition in a two-component lipid-water model are derived and discussed. Experimental data from various concentrations of lipid in the form of droplets and injections under bovine cardiac muscle align with theoretical predictions.

RESULTS

Theoretical and experimental results suggest that the variations of heat capacity and mass density with tissue composition significantly contribute to the amount of optical path length difference measured by OCT phase.

CONCLUSION

PT-OCT has the potential to offer key insights into the chemical composition of the subsurface lipid pools in tissue; however, the interpretation of results needs to be carried out by keeping the nonlinear interplay between the tissue of opto-thermo-physical properties and PT-OCT signals in mind.

Review of the state of the art in cardiovascular endoscopy imaging of atherosclerosis using photoacoustic techniques with pulsed and continuous-wave optical excitations

Intravascular photoacoustics (IV-PA) is an emerging atherosclerosis imaging modality that provides chemical-specific optical information of arterial walls with acoustic depth penetration and resolution. As lipid composition of atherosclerotic plaques is considered to be one of the primary indicators for plaque vulnerability, many IV-PA applications are calibrated so as to target plaque necrotic cores. Based on the mode of optical excitation and the corresponding signal processing technique, IV-PA is categorized into two different modalities. The pulse-based IV-PA has been the universal IV-PA imaging mode with its high peak power and straightforward time-domain signal processing technique. As an alternative, the low power continuous-wave (CW)-based IV-PA has been under intense development as a radar-like frequency-domain signal processing modality. The two state-of-the-art types of IV-PA are reviewed in terms of their physics and imaging capabilities, with major emphasis on frequency-swept CW-based IV-PA that has been recently introduced in the field.