Low background fluorescence 3D-printed micro-lens for imaging of vulnerable atherosclerotic plaques

Vulnerable atherosclerotic plaques, which are prone to rupture, can result in life-threatening events, such as strokes and heart attacks. These plaques are distinguished by features including a large necrotic core, macrophage infiltration, spotty calcification, intraplaque hemorrhage, and a thin fibrous cap. While current intravascular optical coherence tomography (OCT) is capable of visualizing structural characteristics of plaques, such as the fibrous cap thickness, it has limitations in reliably identifying vulnerable plaques. Previous studies have demonstrated that intraplaque hemorrhage and oxidized lipids in the necrotic core and of vulnerable plaques generate autofluorescence when excited at 633 nm. Our team has designed and developed a 3D-printed micro-lens probe that utilizes a photoresist, IP-Visio, with low background fluorescence. This photoresist is ideal for autofluorescence detection of vulnerable plaques in the visible range, without the need for externally injected fluorophores. The micro-lens on the tip of a double clad fiber has two apertures that address the threefold purpose of our probe: OCT imaging, fluorescence excitation, and fluorescence collection by a combination of focal and afocal optical design. With this dual aperture design, we have achieved in capturing the weak autofluorescence signals and high-resolution OCT images from ex vivo human carotid plaques, using the IP-Visio micro-lens intravascular probe. We validated these imaging results with histology and a commercial benchtop fluorescence imaging system. This work paves the way for the wider application of 3D-printed micro-lenses for multimodal OCT and fluorescence imaging in the visible and near-infrared range, especially with intravascular or endoscopic devices.