Imaging Behind the Plaque
Jelle Plomp (TNW-M3I), Ashkan Ghanbarzadeh-Dagheyan (TNW-BMPI), Michel Versluis (TNW-POF), Luuk Spreeuwers (EEMCS – DMB), Guillaume Lajoinie (TNW-POF), Erik Groot Jebbink (TNW-M3I)
Abstract
Introduction: A clear link exists between local blood flow phenomena and the development of atherosclerosis. High frame rate (HFR), contrast-enhanced ultrasound imaging followed by particle image velocimetry (echoPIV) allows studying these flow phenomena in patients. However, atherosclerotic plaques are often calcified, introducing acoustic shadows in which the signal strength received from the contrast agents is limited, leading to incomplete flow quantification. Although globally increasing acoustic pressure during image acquisition would in principle provide an increase in signal strength, it also leads to contrast agent destruction and signal loss.
Objective: To develop a method that improves the signal quality in the acoustic shadow region while only locally increasing the pressure.
Methods: An iterative method was implemented that actively adapts the acoustic pressure transmitted by each transducer element in real-time, based on acquired images. Once optimized, the pressure profile was fixed and used to acquire HFR data. Evaluation was performed in an in vitro setup on 3D printed vessel phantoms that included a wall thickening to induce an acoustic shadow. A fully developed steady laminar flow was used.
Results and Discussion: The transmitted wavefront was actively adapted based on acquired images. In plaque models with an attenuation of 5.6 dB, errors in the obtained flow velocities were reduced from 65% without adaptation to 7.3% with the new iterative method. For attenuation between 7.4 and 14.8 dB, despite being reduced, errors were still larger than 10% after beam adaptation. The developed strategy can potentially also benefit other ultrasound applications affected by acoustic shadows.