Atherosclerosis characterization using lipid-specific photoacoustic imaging and 4D ultrasound strain mapping in mice

Dual-modality photoacoustic tomography (PAT) and four-dimensional ultrasound (4DUS) imaging have recently been used study atherosclerosis progression in small animals. PAT uses pulsed laser light to induce acoustic waves and reconstruct lipid-specific compositional images of tissue. 4DUS captures dynamic volumetric information and can be used to estimate three-dimensional (3D) Green-Lagrange strain using a direct deformation estimation method. Here, we hypothesized that PAT/4DUS can be used to correlate changes in arterial strain and hemodynamics with lipid localization and density in animals that have undergone partial carotid ligation (PCL) induced-atherosclerosis. A 40 MHz transducer (Vevo2100, VisualSonics) and a ND:YAG pulsed laser (Surelite EX, Continuum) were used to image five apolipoprotein-E deficient mice that underwent PCL of the left carotid artery while being fed a Western diet. Animals were imaged using 4DUS at days 0, 1, 4, 7, 10, and 14 to obtain pulsed-wave Doppler for hemodynamic characterization and 4DUS images for strain mapping. At day 14 all animals were euthanized and 3D in situ PAT images of the left carotid artery were acquired using 1210 nm light. The results show that atherosclerotic lesions can be characterized via PAT to localize both lipid accumulation and density and 4DUS to identify regions of low strain.