Photoacoustic Characterization of Vulnerable Plaques

Photoacoustic imaging is a novel modality that allows non-invasive imaging of superficial arteries by combining high ultrasound resolution and high optical tissue contrast. Different wavelengths can be used to target different tissue types, such as collagen, blood, lipid, etc. In the FULLPHASE project, the world’s first handheld, fully integrated PA probe is developed (see link). Pre-clinical validation is performed at the TUE, focusing on perfusion and vulnerability detection of atherosclerosis in superficial arteries (this project).

If plaque builds up in the body's arteries, the condition is called atherosclerosis. Over time, plaque hardens and narrows the arteries. This may limit the flow of oxygen-rich blood to organs and other parts of the body. If plaque builds up in the carotid arteries, a stroke can occur.

 

Currently, intervention planning relies on the severity of the stenosis. However, only one out of six patients benefits from this intervention. So in practice, the severity of the stenosis is not a reliable criteria for the risk of plaque rupture. Plaque rupture occurs when the mechanical stresses in the cap of the plaque exceed the local tissue strength. Therefore, a biomechanical model of the plaque may help to better assess rupture risk. Ultrasound has the ability to provide highly detailed information on plaque geometry and distensibility. Motion tracking techniques can be used to estimate movement of the wall, strains in the wall and flow in the lumen (see ‘Blood in Motion’). However, these data provide quantitative information, and estimates of material properties, but not the actual morphology. Multi-wavelength photo-acoustic imaging can be used to distinguish between different absorbing structures, which provides a more direct assessment of morphology. Therefore, photo-acoustic imaging of the intraplaque hemorrhage and lipid content of the atherosclerotic plaques can be used as a non-invasive tool to investigate the correlation of plaque rupture and the morphology.

New ultrasound techniques, experiments and biomechanical models are developed. In this track, the morphology  of carotid plaques are characterized using photo-acoustics (Umit Arabul), but also via mechanical characterization using functional ultrasound imaging.

Preclinical validation

An experimental framework is developed for 3-D PA US scanning of endarterectomy samples, obtained from the local hospital (CZE), during inflation testing. These surgical samples contain the intima and parts of the medial layer of the plaque. Testing involves pressurization of the fresh tissue right after surgery, semi-3D PA and ultrasound scanning to obtain geometry, determine presence of different constituents, quantify wall motion and strain. Micro-CT imaging or histology is performed to validate the morphology assessment.

 

Before applying these methods to real tissue, and in a later stage patients, the PA/US measurements are also validated and verified in tissue mimicking phantoms (made of polyvinyl alcohol) of straight tubes, stenotic vessels, the latter even including a fatty plaque, and in biological tissue, i.e., porcine carotids obtained at the local slaughterhouse.

Initial in vivo experience

Initial in vivo measurements will be performed to examine the feasibility of non-invasive PA/US imaging of plaques, also including brachial and femoral arteries. Ultimately, a multi-wavelength probe will be used, whereas the current configuration is focused on targeting blood.

Projects

Projects for bachelor-end projects, internships and MSc projects are available.          

  • Development of realistic PA and US phantoms of carotid arteries and plaques including hemorrhage and lipid inclusions
  • Combined Echo-CT and multi-wavelength PA-CT imaging of endarterectomy samples
  • Model-based mechanical characterization of plaques using PA and US imaging
  • Deconvolution algorithm development to improve imaging performance of PA. 

Other projects can be designed in consultation with the supervisors (Ümit Arabul & Richard Lopata)

Students working on this project:Min Wu (PostDoc), Ümit Arabul (PhD project), Femke Vaassen & Osman Akdag (BSc project)