Amaar Qureshi
BME MS Thesis Defense Presentation
Date: 2026-04-10
Time: 1:00 PM - 3:00 PM
Location / Meeting Link: UAW 2100

Committee Members:
Dr. Lindsey Brooks; Dr. Alper Erturk; Dr. Costas Arvanitis


Title: Hybrid Phased Array Transducer for Transcranial Ultrasound Imaging and Guidance of Leaky Lamb Waves to Characterize Intracerebral Hemorrhage

Abstract:
Intracerebral hemorrhage represents only approximately 29% of strokes worldwide but has a relatively high one-month fatality rate of 40%, driven largely by hematoma expansion within the first several hours after onset. Current neuroimaging modalities (CT and MRI) cannot monitor hematoma expansion continuously at the bedside. Transcranial ultrasound offers real-time, portable, radiation-free imaging but is restricted by the skull to narrow acoustic windows that leave peripheral (cortical) regions inaccessible to ultrasound imaging. To address these limitations, this study presents the design, fabrication, and validation of a hybrid phased array transducer capable of operating in two modes. In its conventional imaging mode, the array operates at a center frequency of 690 kHz with a -6 dB fractional bandwidth of 52%, achieving axial and lateral resolutions of 1.3 mm and 1.8 mm, respectively, at a depth of 50 mm. Two bovine blood clots with volumes of 28 mL and 37 mL were embedded in a tissue-mimicking phantom and imaged through a skull-mimicking phantom. In reconstructed three-dimensional images, it was possible to distinguish the 33% volume increase between the two phantoms, which corresponds to the clinical threshold for hematoma expansion. In its guided-wave mode, the array operates as an active acoustic metasurface, guiding waves to propagate within the skull for a controlled distance before leaking into the brain periphery. For evaluation, the array was bonded to a 2.54 mm aluminum plate on the surface of a water tank as a first order approximation of the skull and brain. Under open-circuit conditions at 625 kHz, no guided wave mode exists and acoustic energy radiated diffusely into the water. Next, each passive element in the array transducer was connected to a 10 µH inductive shunt circuit, resulting in a coherent Lamb wave mode with wave propagation along the plate and before leaking energy into the water at controlled angles over the full 90 mm aperture of the array. This electronically switchable guided-wave behavior confirms that piezoelectric boundary condition control can create wave propagation modes that do not exist under passive conditions. Collectively, the imaging and guided-wave results establish the feasibility of a dual-mode transcranial ultrasound imaging system. In the future, such an approach could enable bedside monitoring of intracerebral hemorrhage with an imaging field of view extending beyond the conventional temporal window.