Atherosclerosis, a major cause of heart attacks and strokes, surpasses all types of cancer combined as the leading cause of death in Western societies, representing a significant public health issue. This condition arises when substances like fats and cholesterol build up in artery walls, causing them to thicken and stiffen. If a plaque in these blood vessels ruptures or fragments, it can lead to a heart attack or stroke. Now, researchers have invented a novel catheter-based device that combines two sophisticated optical techniques to image dangerous plaques in arteries supplying blood to the heart. By revealing new details about plaques, this device could be instrumental in enhancing treatments to prevent heart attacks and strokes.

Much of the current knowledge about atherosclerosis's formation and progression stems from histopathology studies on postmortem coronary specimens. Although the advent of intravascular ultrasound and OCT has enabled plaque study in living patients, more effective methods and tools are needed to investigate atherosclerosis. To meet this need, a team at the University of California, Davis (Davis, CA, USA) designed the new, flexible device that combines fluorescence lifetime imaging (FLIM) and polarization-sensitive optical coherence tomography (PSOCT). This device captures rich information on the composition, shape, and microstructure of atherosclerotic plaques.

This multi-year project undertaken by the UC Davis researchers focused on developing multispectral FLIM for intravascular imaging which can reveal information like extracellular matrix composition, inflammation presence, and artery calcification levels. Previously, the researchers had combined FLIM with intravascular ultrasound; in their latest endeavor, they combined it with PSOCT. PSOCT provides detailed morphological data and measurements of birefringence and depolarization. Utilizing FLIM and PSOCT together delivers an unparalleled insight into plaque morphology, microstructure, and biochemical composition.

Developing multimodal intravascular imaging systems suitable for coronary catheterization presents technological challenges. It requires extremely thin (less than 1 mm), flexible catheters capable of navigating vessels with sharp twists and turns. A high imaging speed of about 100 frames/second is crucial to minimize cardiac motion artifacts for proper arterial imaging. To integrate FLIM and PSOCT without impairing either technique's performance, the researchers used suitable optical components. A newly designed rotary collimator with high light transmission and significant return loss was vital for effective PSOCT performance. Their catheter system matches the dimensions and flexibility of current intravascular imaging devices in clinical use.

Initial tests with artificial tissue validated the basic functionality of the new system, followed by the successful measurement of a healthy coronary artery from a pig. Subsequent in vivo tests in swine hearts showed the hybrid catheter system's capability, paving the way for clinical validation. These tests confirmed the system's ability to simultaneously gather co-registered FLIM data across four spectral bands and PSOCT information on backscattered intensity, birefringence, and depolarization. The next steps involve using the intravascular imaging system to examine plaques in ex vivo human coronary arteries. By comparing the optical signals with plaque characteristics identified by expert pathologists, the researchers aim to better understand which features FLIM-PSOCT can identify and develop predictive models. They also plan further testing towards clinical validation of the system in patients.

“Better clinical management made possible by advanced intravascular imaging tools will benefit patients by providing more accurate information to help cardiologists tailor treatment or by supporting the development of new therapies,” said research team member leader Laura Marcu from University of California, Davis.

“With further testing and development, our device could be used for longitudinal studies where intravascular imaging is obtained from the same patients at different timepoints, providing a picture of plaque evolution or response to therapeutic interventions,” added Julien Bec, first author of the paper. “This will be very valuable to better understand disease evolution, evaluate the efficacy of new drugs and treatments and guide stenting procedures used to restore normal blood flow.”

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