Laser-generated focused ultrasound for thrombus characterization and fragmentation: ex vivo feasibility study

Intravascular thrombus poses a significant risk for ischemic events, yet precise characterization and selective mechanical intervention remain challenging. Here, we present a laser-generated focused ultrasound (LGFU) platform incorporating a long-focused photoacoustic lens (focal length: 28 mm), which achieved a 1.79-fold increase in penetration depth compared with previously reported LGFU systems while maintaining a tight focal spot (60 μm lateral, 150 μm axial) and broadband acoustic output (- 6 dB bandwidth: ~ 15 MHz). Unlike previously reported LGFU systems developed primarily for therapeutic applications, the present platform combines LGFU-based ultrasound generation with co-aligned hydrophone reception for spectral characterization of thrombi under vessel-mimicking phantom conditions. Empirical mode decomposition (EMD) applied to complex backscattered signals enabled discrimination of thrombus thicknesses down to ~ 100 μm, highlighting the utility of broadband photoacoustic signals for sub-millimeter spectral characterization. Finite-element simulations supported the thickness-dependent spectral shift underlying this discrimination. Then, we confirmed that thrombus fragmentation linewidths were dependent on an input laser energy, which was evaluated by using a photoacoustic lens with a 15 mm focal length. Finally, fragmentation of the vessel-mimicking phantom was demonstrated with a longer focal length (28 mm). The observed fragmentation behavior was consistent with cavitation-mediated mechanical effects under the tested conditions. These results support the feasibility of an LGFU platform for combined thrombus characterization and localized fragmentation under proof-of-concept phantom and ex vivo conditions.