Abstract
As lipid composition of atherosclerotic plaques is considered to be one of the primary indicators for plaque vulnerability, a diagnostic modality that can sensitively evaluate their necrotic core is highly desirable in atherosclerosis imaging. In this regard, intravascular photoacoustic (IVPA) imaging is an emerging plaque detection modality that provides lipid-specific chemical information of arterial walls. Within the near-infrared window, a 1210-nm optical source is usually chosen for IVPA applications because lipid exhibits a strong absorption peak at that wavelength. However, other arterial tissues also show some degree of absorption near 1210 nm and generate undesirable interfering PA signals. In this study, a novel wavelength-modulated Intravascular Differential Photoacoustic Radar (IV-DPAR) modality was introduced as an interference-free detection technique for a more accurate and reliable diagnosis of plaque progression. By using two low-power continuous-wave laser diodes in a differential manner, IV-DPAR could efficiently suppress undesirable absorptions and system noise, while dramatically improving system sensitivity and specificity to cholesterol, the primary ingredient of plaque necrotic core. When co-registered with intravascular ultrasound imaging, IV-DPAR could sensitively locate and characterize the lipid contents of plaques in human atherosclerotic arteries, regardless of their size and depth.
Highlights
A few of today’s widely employed atherosclerosis imaging modalities include X-ray angiography, intravascular ultrasound (IVUS) and optical coherence tomography (OCT)
In the Center for Advanced Diffusion-wave and Photoacoustic Technologies (CADIPT), University of Toronto, a PA imaging method has been under intense development based on frequency-modulated optical excitation with low power continuous wave (CW) lasers and frequency-domain (FD) signal processing
During the calibration, when the amplitude ratio of s1210(t) and s980(t) from any noise source is adjusted to be ~1, the intravascular differential PA radar (IV-DPAR) system will highly suppress www.nature.com/scientificreports those unwanted absorptions or system noise to approximately zero baseline by means of complete destructive interference, while amplifying weak PA signals emerging from the cholesterol contents of plaques. This study demonstrates this main principle of IV-DPAR by imaging pig and human atherosclerotic arteries ex vivo using the assembled IV-DPAR catheter prototype
Summary
A few of today’s widely employed atherosclerosis imaging modalities include X-ray angiography, intravascular ultrasound (IVUS) and optical coherence tomography (OCT). This modality is called the Photoacoustic Radar (PAR) and has been shown to be competitive with conventional pulsed-based PA systems, providing high signal-to-noise ratio (SNR), sub-mm axial resolution and depth-resolved/molecularly specific optical contrast of the subsurface tissue chromophores, while utilizing low power irradiation and a narrowband detector[13,14].
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