Interference-free Detection of Lipid-laden Atherosclerotic Plaques by 3D Co-registration of Frequency-Domain Differential Photoacoustic and Ultrasound Radar Imaging

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.

Effects of lipid composition on photothermal optical coherence tomography signals

“… 13 , 14 Mayo is primarily composed of lipids, which provide an absorption signature that can be targeted with PT-OCT, and its lipid composition is similar to that of atherosclerotic plaques. 13 , 14 Since the composition and lipid content play a critical role in determining the propensity of a plaque to rupture, 15 PT-OCT may offer the prospect to leverage the same contrast mechanism as that used by near-infrared spectroscopy 16 and photoacoustic imaging 17 – 19 (i.e., absorption of lipid) for plaque composition imaging, albeit with much finer resolution.…”