Dual-modality fiber-based OCT-TPL imaging system for simultaneous microstructural and molecular analysis of atherosclerotic plaques

Molecular Imaging and Non-molecular Imaging of Atherosclerotic Plaque Thrombosis

Thrombosis in the context of atherosclerosis typically results in life-threatening consequences, including acute coronary events and ischemic stroke. As such, early detection and treatment of thrombosis in atherosclerosis patients is essential. Clinical diagnosis of thrombosis in these patients is typically based upon a combination of imaging approaches. However, conventional imaging modalities primarily focus on assessing the anatomical structure and physiological function, severely constraining their ability to detect early thrombus formation or the processes underlying such pathology. Recently, however, novel molecular and non-molecular imaging strategies have been developed to assess thrombus composition and activity at the molecular and cellular levels more accurately. These approaches have been successfully used to markedly reduce rates of atherothrombotic events in patients suffering from acute coronary syndrome (ACS) by facilitating simultaneous diagnosis and personalized treatment of thrombosis. Moreover, these modalities allow monitoring of plaque condition for preventing plaque rupture and associated adverse cardiovascular events in such patients. Sustained developments in molecular and non-molecular imaging technologies have enabled the increasingly specific and sensitive diagnosis of atherothrombosis in animal studies and clinical settings, making these technologies invaluable to patients' health in the future. In the present review, we discuss current progress regarding the non-molecular and molecular imaging of thrombosis in different animal studies and atherosclerotic patients.

Label-free imaging of atherosclerotic plaques using third-harmonic generation microscopy

Multiphoton microscopy using laser sources in the mid-infrared range (MIR, 1,300 nm and 1,700 nm) was used to image atherosclerotic plaques from murine and human samples. Third harmonic generation (THG) from atherosclerotic plaques revealed morphological details of cellular and extracellular lipid deposits. Simultaneous nonlinear optical signals from the same laser source, including second harmonic generation and endogenous fluorescence, resulted in label-free images of various layers within the diseased vessel wall. The THG signal adds an endogenous contrast mechanism with a practical degree of specificity for atherosclerotic plaques that complements current nonlinear optical methods for the investigation of cardiovascular disease. Our use of whole-mount tissue and backward scattered epi-detection suggests THG could potentially be used in the future as a clinical tool.

Diagnosis of Thin-Capped Fibroatheromas in Intravascular Optical Coherence Tomography Images: Effects of Light Scattering

BACKGROUND

Intravascular optical coherence tomography (IVOCT) images are recorded by detecting light backscattered within coronary arteries. We hypothesize that non-thin-capped fibroatheroma (TCFA) causes may scatter light to create the false appearance of IVOCT TCFA.

METHODS AND RESULTS

Ten human cadaver hearts were imaged with IVOCT (n=14 coronary arteries). IVOCT and histological TCFA images were coregistered and compared. Of 21 IVOCT TCFAs (fibrous cap <65 μm, lipid arc >1 quadrant), only 8 were true histological TCFA. Foam cell infiltration was responsible for 70% of false IVOCT TCFA and caused both thick-capped fibroatheromas to appear as TCFA, and the appearance of TCFAs when no lipid core was present. Other false IVOCT TCFA causes included smooth muscle cell-rich fibrous tissue (12%) and loose connective tissue (9%). If the lipid arc >1 quadrant (obtuse) criterion was disregarded, 45 IVOCT TCFAs were identified, and sensitivity of IVOCT TCFA detection increased from 63% to 87%, and specificity remained high at 92%.

CONCLUSIONS

We demonstrate that IVOCT can exhibit 87% (95% CI, 75%-93%) sensitivity and 92% specificity (95% CI, 86%-96%) to detect all lipid arcs (both obtuse and acute, <1 quadrant) TCFA, and we also propose new mechanisms involving light scattering that explain why other plaque components can masquerade as TCFA and cause low positive predictive value of IVOCT for TCFA detection (47% for obtuse lipid arcs). Disregarding the lipid arc >1 quadrant requirement enhances the ability of IVOCT to detect TCFA.

Analyzing spatial correlations in tissue using angle-resolved low coherence interferometry measurements guided by co-located optical coherence tomography

Angle-resolved low coherence interferometry (a/LCI) is an optical technique used to measure nuclear morphology in situ. However, a/LCI is not an imaging modality and can produce ambiguous results when the measurements are not properly oriented to the tissue architecture. Here we present a 2D a/LCI system which incorporates optical coherence tomography imaging to guide the measurements. System design and characterization are presented, along with example cases which demonstrate the utility of the combined measurements. In addition, future development and applications of this dual modality approach are discussed.

Characterizing the lacrimal punctal region using anterior segment optical coherence tomography

PURPOSE

Abnormalities of lacrimal punctum size and morphology probably contribute to excess tearing, with significant effects on quality-of-life for affected individuals. Our current understanding of normal punctal morphology originates from ex vivo studies, which are unlikely to capture the true nature of the living punctum. This study used enhanced depth anterior segment optical coherence tomography (OCT) to give improved characterization and understanding of lacrimal punctal structure.

METHODS

Qualitative and quantitative assessments were performed on spectral domain OCT images collected prospectively from 40 lower puncta of 20 healthy volunteers.

RESULTS

The average external lower lid punctal diameter was 0.646 mm (SD 150 μm) on OCT imaging, measured at the largest diameter, which was in parallel to the mucocutaneous junction. Fifty-five per cent of puncta appeared closed, whilst the eyelids were open. Fluid menisci were visible within 73% of puncta. A postpunctal 'ampulla' was visible within three systems, one of which was imaged through the conjunctival surface. Ampullary dilatation occurred laterally, rather than at the medial wall.

CONCLUSION

Optical coherence tomography provides quick and non-invasive assessment of the lacrimal punctum and its neighbouring tissue layers. This assessment of punctal size and morphology has the potential for further investigation of punctal physiology, for aiding diagnosis, and for monitoring the results of treatment. The average external diameter of the punctal opening measured in this study is greater than that recorded in anatomical textbooks.