Catheter Combines Ultrasound and Multispectral Fluorescence to Measure Arterial Plaque

A novel cardiac catheter probe combines intravascular ultrasound (IVUS) and fluorescence lifetime imaging (FLIM) in a single device that can image the arteries of a living heart. The catheter can simultaneously retrieve structural and biochemical information about arterial plaque that could help physicians more reliably predict heart attacks.

Researchers at the University of California, Davis, integrated IVUS and FLIM elements into a compact, single rotational intravascular catheter. An optical fiber in the catheter sends short laser pulses into surrounding tissue, which responds by fluorescing. Different kinds of tissue (collagen, proteins, lipids) emit different amounts of fluorescence. At the same time, an ultrasound probe in the catheter records structural information about the blood vessel.

Biomedical engineers at UC Davis have combined intravascular ultrasound with fluorescence lifetime imaging in a single catheter probe that can image the tiny arteries of a living heart. The new catheter can simultaneously retrieve structural and biochemical information about arterial plaque. Courtesy of Marcu Lab/UC Davis.

The penetration depth of the UV light used for excitation (about 200 µm) provides a sectioning effect by limiting the interrogated volume to the superficial layer, considered to be of particular relevance to plaque characterization.

Integration of the FLIM imaging modality was achieved without negatively impacting the performance of the clinical IVUS component.

The ability of the system to acquire robust bi-modal data in coronary arteries in vivo using standard percutaneous coronary intervention techniques in combination with a Dextran solution bolus flush was demonstrated in healthy swine. Imaging of a few representative diseased human samples was performed and showed that different types of lesions in diseased coronary arteries, identified via histology, were characterized by FLIM biochemical signatures consistent with findings from earlier studies performed by the group.

The catheter used in the study is flexible enough to access coronary arteries in a living human following standard procedures. It does not require any injected fluorescent tracers or any special modification of the catheterization procedures.

The team believes that the combination of FLIM with a morphological imaging modality such as IVUS is important because FLIM alone cannot provide morphometric information about lumen size, geometry or direct measurement of lesion size. When projected onto the vessel lumen boundary identified by IVUS, the dimensions of FLIM features can be precisely assessed.

The combination FLIM-IVUS imaging catheter could provide a comprehensive insight into how atherosclerotic plaque forms, aiding diagnosis and providing a way to measure how plaques shrink in response to therapy.

The team believes that current results support further interrogation of a large number of coronary samples, and studies designed to demonstrate statistical differences between distinct coronary plaque subtypes. The trend toward increased frame rate for the next generation of clinical IVUS will be leveraged to build a faster FLIM/IVUS system.

The research team, led by professor Laura Marcu, is currently working to obtain FDA approval to test this new intravascular technology on human patients.

The research was published in Scientific Reports (doi:10.1038/s41598-017-08056-0).

These videos visualize how the probe images an artery. Courtesy of Marcu Lab/UC Davis.