Detecting and evaluating vulnerable artery plaque with handheld photoacoustic imaging system

Aortic atherosclerotic plaque rupture can cause cerebral and cardiac infarction. Detecting lipid-rich vulnerable plaque early is important to prevent plaque rupture. However, using conventional modalities to evaluate such plaques is difficult. Photoacoustic imaging can elucidate tissue characteristics. Some lipid-rich plaque evaluations have used intravascular photoacoustic imaging systems. A handheld photoacoustic imaging system was developed to reduce invasiveness and to ease handling. Lipid-rich plaque detection capability was evaluated using phantom experiments. Mimic plaques (comprising oleic acid cholesterol and linoleic acid cholesterol) are embedded into a silicone tube. The silicone tube is filled with ovine blood. These objects were fixed in a water with black ink and biological tissue (chicken breast). For observation, laser light is guided to the model phantom surface by an optical fiber bundle close to the linear ultrasound probe. The photoacoustic signal distributions are then recorded as photoacoustic images. The photoacoustic images, obtained for which wavelengths where lipid light absorbance is high, show strong photoacoustic signals from the mimic plaque at a depth of human carotid artery. At wavelengths of 1150-1300 nm, similarity between photoacoustic spectra and the absorption spectrum of lipid was evaluated by calculating the correlation coefficient in photoacoustic images. Results show high correlation at the mimic plaque. Results demonstrate that the detection of lipid-rich plaque can be done, even optical properties (e.g. scattering coefficient and absorption coefficient) of the surrounding tissue were inhomogeneous. Future studies must conduct in vivo experiments and examine optimization to improve SNR.