Bi-modal imaging of atherosclerotic plaques: Automated method for co-registration between fluorescence lifetime imaging and intravascular ultrasound data Dimitris Gorpas a , Hussain Fatakdawala a , Julien Bec a , Dinglong Ma a , Diego R. Yankelevich a,b , John W. Bishop c , Jinyi Qi a , Laura Marcu *a a Dept. of Biomedical Engineering, University of California - Davis, Davis, CA, USA; b Dept. of Electrical and Computer Engineering, University of California - Davis, Davis, CA, USA, c Dept. of Pathology and Laboratory Medicine, University of California - Davis Medical Center, Sacramento, CA, USA ABSTRACT The risk of atherosclerosis plaque rupture cannot be assessed by the current imaging systems and thus new multi-modal technologies are under investigation. This includes combining a new fluorescence lifetime imaging (FLIm) technique, which is sensitive to plaque biochemical features, with conventional intravascular ultrasound (IVUS), which provides information on plaque morphology. In this study we present an automated method allowing for the co-registration of imaging data acquired based on these two techniques. Intraluminal studies were conducted in ex-vivo segments of human coronaries with a multimodal catheter integrating a commercial IVUS (40 MHz) and a rotational side-viewing fiber based multispectral FLIm system (355 nm excitation, 390±20, 452±22 and 542±25 nm acquisition wavelengths). The proposed method relies on the lumen/intima boundary extraction from the IVUS polar images. Image restoration is applied for the noise reduction and edge enhancement, while gray-scale peak tracing over the A-lines of the IVUS polar images is applied for the lumen boundary extraction. The detection of the guide-wire artifact is used for the angular registration between FLIm and IVUS data, after which the lifetime values can be mapped onto the segmented lumen/intima interface. The segmentation accuracy has been assessed against manual tracings, providing 0.120±0.054 mm mean Hausdorff distance. This method makes the bi-modal FLIm and IVUS approach feasible for comprehensive intravascular diagnostic by providing co-registered biochemical and morphological information about atherosclerotic plaques. Keywords: Intravascular ultrasound, fluorescence lifetime imaging, image segmentation, image restoration, co- registration 1. INTRODUCTION Coronary artery disease remains the leading cause of death worldwide, despite the efforts placed towards its early diagnosis and treatment 1 . Atherosclerotic plaque susceptibility to rupture is related to its biochemical compositions, which, however, cannot be addressed by the current clinical imaging modalities, as they can only provide anatomical information and are focused mostly on stenosis, the cause of stable angina 2 . The availability of a clinical tool that would provide combined structural and biochemical information of the imaged vessels will be valuable to the interventional cardiologists towards the assessment of the complex nature of atherosclerosis and the detection of vulnerable atheroma before rupture. During the last few years new multi-modal technologies are under investigation 2-7 . One such technology has been developed by our group and includes the combination of fluorescence lifetime imaging (FLIm), which has demonstrated potential of assessing the plaque biochemical features, with conventional intravascular ultrasound (IVUS), which is the gold-standard technique for assessing the plaque morphology 8, 9 . The great challenge in the successful development of these multimodal systems is the co-registration of the acquired data. This is addressed through the extraction of the vessel luminal boundary from the structural modality and the mapping onto it of the biochemical data. In the context of IVUS imaging, the extraction of the luminal boundary is referred as segmentation, and is one of the most studied problems in IVUS image processing 7, 10, 11 . However, most clinical applications requiring segmentation of * lmarcu@ucdavis.edu; phone: (530) 752-0288; http://www.bme.ucdavis.edu/marculab/ Photonic Therapeutics and Diagnostics X, edited by Bernard Choi, et al., Proc. of SPIE Vol. 8926, 892638 · © 2014 SPIE · CCC code: 1605-7422/14/$18 · doi: 10.1117/12.2040311 Proc. of SPIE Vol. 8926 892638-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 11/25/2014 Terms of Use: http://spiedl.org/terms