A team of biomedical engineers and ophthalmologists at the University of Southern California (USC) has pioneered a breakthrough 4D ultrasound imaging technique that maps the mechanical properties of ocular tissue in unprecedented, volumetric detail. Published in BME Frontiers, a Science Partner Journal, the study introduces a novel "sequential excitation" method that overcomes longstanding hardware barriers, offering a highly accessible and affordable pathway for diagnosing and monitoring complex eye diseases such as glaucoma.
For decades, shear wave elastography (SWE) has been a valuable clinical tool for non-invasively measuring tissue stiffness. However, conventional SWE is largely confined to 2D imaging. Capturing true 3D or 4D (x, y, z, t) volumetric data typically requires expensive, fully populated multi-channel ultrasound systems with thousands of synchronized channels, making widespread clinical adoption prohibitively costly. Furthermore, 2D imaging fails to capture tissue anisotropy—the directional variation in mechanical properties that is critical for accurately characterizing complex biological structures.
To bridge this gap, Dr. Qifa Zhou and his interdisciplinary team at USC developed an optimized sequential excitation framework. By strategically dividing a 1,024-element 2D matrix array into four independent subpanels and connecting them to a standard, widely available 256-channel ultrasound system via multiplexing, the researchers achieved high-fidelity volumetric imaging without the need for costly, custom-built hardware.
The team further enhanced image quality by implementing a "swept-cross compounding" strategy. This innovative approach effectively mitigates signal gaps between array panels, dramatically improving spatial resolution. In phantom tests, the technique improved elevational resolution from 0.84 mm to 0.35 mm at a 10-mm depth and significantly sharpened the 3D point spread function.
The method's clinical potential was rigorously validated in both ex vivo tissue models and live rabbit experiments. In a landmark achievement, the researchers successfully performed the 4D shear wave velocity mapping of a living rabbit cornea. The volumetric maps clearly demonstrated that corneal stiffness increases proportionally with intraocular pressure (IOP)—a vital biomarker for glaucoma and other pressure-related ocular pathologies. Additionally, the system accurately differentiated tissue anisotropy and estimated muscle fiber orientation in ex vivo samples, proving its capability to capture complex, directional biomechanical data.
"This sequential approach provides a practical balance between hardware simplicity and advanced volumetric imaging capability," said Dr. Qifa Zhou, corresponding author and professor at USC. "By making 4D elastography more accessible and cost-effective, we open new doors for non-invasive, quantitative assessment of ocular biomechanics. This could fundamentally change how we monitor IOP-dependent diseases, especially in cases where traditional tonometry is impractical."
BME Frontiers
Experimental study
Animals
Four-Dimensional Sequential Elastography for Ocular Tissue Using 2D Matrix Array
9-Sep-2026