Hybrid phased array transducer for transcranial ultrasound imaging and guidance of leaky Lamb waves to characterize intracerebral hemorrhage

1.2 to 1.8 million people worldwide experience a new intracerebral hemorrhage (ICH) each year. ICH is a subtype of stroke associated with high morbidity and mortality in which nearly 40% of patients experience significant hematoma growth within the first 24 hours. Hematoma expansion is associated with worse clinical outcomes, thus tracking of hematoma evolution may inform critical management decisions. Conventional transcranial ultrasound imaging is limited in its ability to image the periphery of the brain close to the skull and thus cannot visualize peripheral hematomas. To address these limitations, we designed and fabricated a 60-element hybrid phased array transducer capable of dual-mode operation: (1) conventional B-mode imaging at ~1 MHz and (2) guided Lamb wave generation and controlled acoustic leakage into targeted regions close to the skull. The fabricated array had a center frequency of 1.3 MHz and a -6 dB bandwidth of 51%. At depth of 5 cm, the measured axial resolution was 0.96 mm, the lateral resolution was 1.94 mm, and the SNR was 24.7 dB. In addition, in simulations and experiments, the array successfully generated and controlled Lamb wave propagation in a skull-mimicking aluminum plate. By electrically tuning individual elements with shunt inductors, the system could toggle between "leaky" and "non-leaky" guided wave modes, effectively acting as an active acoustic metasurface on the skull. This could improve ultrasound delivery to locations inside the skull that are typically inaccessible.