Abstract
Intravascular photoacoustic-ultrasound (IVPA-US) imaging is an emerging hybrid modality for the detection of lipid-laden plaques, as it provides simultaneous morphological and lipid-specific chemical information of an artery wall. Real-time imaging and display at video-rate speed are critical for clinical utility of the IVPA-US imaging technology. Here, we demonstrate a portable IVPA-US system capable of imaging at up to 25 frames per second in real-time display mode. This unprecedented imaging speed was achieved by concurrent innovations in excitation laser source, rotary joint assembly, 1 mm IVPA-US catheter size, differentiated A-line strategy, and real-time image processing and display algorithms. Spatial resolution, chemical specificity, and capability for imaging highly dynamic objects were evaluated by phantoms to characterize system performance. An imaging speed of 16 frames per second was determined to be adequate to suppress motion artifacts from cardiac pulsation for in vivo applications. The translational capability of this system for the detection of lipid-laden plaques was validated by ex vivo imaging of an atherosclerotic human coronary artery at 16 frames per second, which showed strong correlation to gold-standard histopathology. Thus, this high-speed IVPA-US imaging system presents significant advances in the translational intravascular and other endoscopic applications.
Highlights
Coronary artery disease remains the leading cause of morbidity and mortality throughout the world
In the system, a 1.7 μm, 2 kHz master oscillator power amplifier (MOPA)-pumped optical parametric oscillator (OPO) was used for high-speed optical excitation
The sequentially generated PA and US signals were detected by the intravascular photoacoustic-ultrasound (IVPA-US) catheter, transmitted by the slip ring, amplified by Figure 2. 1.7 μm 2 kHz MOPA-pumped OPO for high-speed optical excitation. (a) Schematic of MOPApumped OPO
Summary
Coronary artery disease remains the leading cause of morbidity and mortality throughout the world. Intravascular optical coherence tomography can accurately detect fibrous cap thickness with micron-scale resolution[16], but lacks sufficient imaging depth and chemical selectivity to wholly determine plaque composition These gaps, along with the increasing prevalence of coronary artery disease, highlight an unmet clinical need for a chemically-selective imaging modality with spatial resolution to advance the detection, understanding, and treatment of lipid-laden vulnerable plaques. The IVPA-US imaging technology is currently under active investigation for the identification of various tissue components[21, 23, 24], contrast mechanism[21, 22], optical excitation sources[25,26,27], IVPA-US catheter designs[27,28,29,30,31], and ex vivo and preclinical validations[32,33,34] These works are limited by the use of slow imaging speeds (up to 5 frames per second (fps)27) as well as lack of real-time image display, which are necessary components for future in vivo applications where imaging must be at a sufficient speed to avoid motion artifacts from cardiac pulsation. These developments enabled the 25 fps imaging speed, a 5 times improvement over any previously reported IVPA-US imaging speed and comparable to the imaging speeds of current commercial IVUS and NIRS-IVUS systems[35]
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