Staging atherosclerosis using ultrasound, strain and photoacoustic imaging

The rupture of atherosclerotic plaques represents one of the leading causes of morbidity and mortality. The aim of our study is to assess the morphology, functionality and composition of plaques formed in common carotid artery using a non-invasive in-vivo imaging technology, namely combined ultrasound, strain and photoacoustics. The imaging approach was tested ex-vivo on excised rabbit aortas (two with and two without plaques) using the integrated vascular imaging probe. The artery was flushed with blood at a pulsatile flow (1.5 Hz pulse rate and 50 m/s flow velocity). Ultrasound B-mode images and strain images, recorded at 296 frames per second, were obtained using a 12 MHz linear array transducer. For photoacoustic imaging the same ultrasound transducer was coupled with 19 optical fibers connected to OPO laser system (operated at 5 ns pulse duration, 590 nm and 700 nm spectral range). To analyze the advantages of the three imaging techniques, hyper- and hypoechogenic regions were separately isolated and the corresponding strain and photoacoustic signals were compared. Spatial variations in ultrasound echogeneicity are related to changes in arterial structure and function, i.e. hyperechogenic regions correspond to 15% or more decrease in peak strain rate and correlate with fibrotic tissue (as identified by photoacoustic images). The results of our study suggest that combined ultrasound, strain and photoacoustic imaging provides complementary information. Analysis of co-registered ultrasound, strain and photoacoustic images can be used to differentiate morphology, functionality and composition of plaques necessary for clinical diagnosis.