Fluorescence Lifetime Imaging (FLIm) enables label-free characterization of tissue composition based on distinct spectral and temporal fluorescence signatures from biological samples. We leverage a database of intraluminal FLIm-IVUS imaging data associated with histological findings to demonstrate the detection of foam cells(540-nm lifetime increase, ROC-AUC=0.94 for foam cell infiltration >25%), superficial calcium (450-nm lifetime decrease), and regions of active plaque formation (390-nm lifetime increase). The ability of FLIm to provide information that complements existing intravascular imaging modalities opens new perspectives to improve our understanding of plaque development and improve risk assessment in patients at risk of acute coronary events.
KEYWORDS: Luminescence, Microsoft Foundation Class Library, Visualization, Intravascular ultrasound, Arteries, Imaging systems, In vivo imaging, Fluorescence lifetime imaging, Tissues, Biological research
Fluorescence Lifetime Imaging (FLIm) is a label-free technique that provides biochemical information from biological samples derived from tissue autofluorescence. Using a custom multispectral FLIm/IVUS catheter system, fluorescence lifetime data (n=33,980 locations) was collected from ex vivo human artery segments (n=32 samples). Our findings indicate that intravascular spectroscopy with FLIm supports the identification of early progression-prone lesions, characterized by the accumulation of extracellular lipids, as well as the quantification of inflammatory activity, characterized by macrophage foam cells accumulation. This information improves our understanding of plaque development, which may ultimately be used to improve risk assessment of acute coronary events.
We report the design and validation of a novel ball lens-based imaging catheter based on dual-clad fiber for frequency-domain fluorescence lifetime imaging microscopy (FLIM) of atherosclerosis. The illumination and collection performance of the catheter endoscope was modeled and optimized with the ray-tracing program Zemax. A 1.55-m-long dual-clad fiber was spliced with a short length of coreless fiber, and then heated and polished to fabricate the angled ball lens. The fiber endoscope was enclosed in a torque cable and had a diameter of 2Fr. The catheter was affixed to a custom built lensless rotary joint which had high coupling efficiency (>90%) over a broad spectral range, accommodating both the UV (375 nm) excitation and the broad fluorescence emission (385 nm - 600 nm). The computer controlled rotary joint and translation stage for pullback imaging can routinely achieve rotation rates of 6000 rpm. The endoscope has two configurations depending on different illumination methods. Lateral resolution was improved more than twice by illuminating the core instead of the inner cladding, while SNR decreased due to higher attenuation of the core. Experiments conducted using a resolution target demonstrate a lateral resolution 80 μm at 1 mm lens-to-sample distance. Experiments conducted using a fluorescein phantom and a segment of ex vivo human coronary artery demonstrate the system performance for fluorescence lifetime imaging with pullback velocities of >10mm/s. This study demonstrates the novel design of a ball lens-based FLIM catheter system to record fluorescence in a continuous helical scanning method across broad-spectral emission bands.
FL-IVUS combines intravascular ultrasound with fluorescence lifetime imaging to obtain morphologic and biochemical details from the arterial wall. Ultrasound measurements alone provide morphologic information (plaque burden, remodeling index and presence of calcium). Fluorescence lifetime can determine the presence of a thick fibrous cap, macrophage infiltration, and lipid cores beneath thin fibrous caps. These details are important to assess plaque vulnerability. In this study, we focused on the ability of FL-IVUS to differentiate between early and advanced lipid cores-advanced cores are vulnerable to rupture. We imaged N=12 ex vivo human coronary arteries and performed hematoxylin and eosin, Movat’s pentachrome and CD68 immunohistochemistry at 500 micron intervals throughout the length of the vessels. We found only N=1 thin-capped fibroatheroma (TCFA) with an advanced necrotic core and N=7 cases of foam cell infiltration, early lipid cores or deep necrotic cores. IVUS was able to observe the increased plaque burden and calcification of the advanced and deep necrotic cores, but could not identify early lipid cores, foam cell infiltration or discriminate between deep necrotic cores and TCFA. The addition of FLIm to IVUS allowed the TCFA to be discriminated from early lipid accumulation, particularly at 542±50 nm (355 nm pulsed excitation): 7.6 ± 0.5 ns compared to 6.6 ± 0.4 ns, respectively (P<0.001 by ANOVA analysis). These differences need to be validated in a larger cohort, but exist due to specific lipid content in the necrotic core as well as increased extracellular matrix in early lesions.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.