Development and Characterization of an Intravascular Ultrasonic-Photoacoustic (IVUP) Endoscope for Medical Imaging

Abstract

Intravascular ultrasound (IVUS) imaging is extremely important for detection and characterization of high-risk atherosclerotic plaques as well as gastrointestinal diseases. Recently, intravascular photoacoustic (IVPA) imaging has been used to differentiate the composition of biological tissues with high optical contrast and ultrasonic resolution. The objective of the current study was to demonstrate that the combination of these imaging techniques could provide morphological information and molecular screening to characterize abnormal tissues, which would help physicians to ensure vital therapeutic value and prognostic significance for patients before commencing therapy. In this study, by integrating a high-frequency IVUS imaging catheter (45 MHz, single-element, unfocused, 0.7 mm in diameter) with a multi-mode side-firing optical fiber (0.6 mm in core diameter and 0.22 NA), a 2.2-mm outer diameter integrated intravascular ultrasonic-photoacoustic (IVUP) imaging catheter was developed to provide spatial and functional information on light distribution in a turbid sample. Simultaneously, IVUS imaging was co-registered to IVPA imaging to construct 3D volumetric IVUP image of the sample. For phantom studies, polyvinyl alcohol (PVA) tissue-mimicking arterial vessel phantoms injected with indocyanine green (ICG), methylene blue and macrophages loaded with ICG inclusions were used to demonstrate the feasibility of mapping the biological dyes, which are currently used in cardiovascular and cancer diagnostics. For ex vivo studies, an excised sample of pig intestine injected with ICG was utilized to target the biomarkers present in the gastrointestinal tumors with the proposed hybrid technique. The excised samples of pig arteries injected with macrophages labeled by ICG were also used to demonstrate the feasibility of the IVUP endoscope to detect vulnerable plaques. The IVUP imaging clearly reveals both the structure and composition of the samples. The results indicated that IVUP endoscope with the 2.2-mm diameter catheter could be a useful tool for medical imaging.