Four-Dimensional Sequential Elastography for Ocular Tissue Using 2D Matrix Array.

Objective: This study aims to facilitate a sequential excitation 4-dimensional (4D) ultrasound shear wave elastography (SWE) method for volumetric characterization of mechanical properties of ocular tissue using a 2D matrix array with a standard 256-channel ultrasound system. Impact Statement: Sequential elastography (SE) enables cost-effective 4D volumetric elastography without requiring an equal channel-count system. The swept-cross strategy improves volumetric imaging quality and, for the first time, enables 4D SWE-based differentiation of tissue anisotropy, with in vivo ocular applications. Introduction: Volumetric SWE remains challenging because of the limited channel counts of the acquisition system. Methods: SE applies a 32 × 32 matrix array and divides it into four 8 × 32 subpanels, connected with a Vantage 256 system through 4-1 multiplexing. An optimized sequential excitation and swept-cross compounding method is used to reduce the interpanel gap influence and improve elevational performance. Results: Validated using wire targets, point target, ex vivo chicken breast, and in vivo rabbit cornea, SE improved volumetric imaging performance compared with conventional subpanel compounding. It improved the elevational resolution from 0.84 mm to 0.35 mm at 10-mm depth and the 3D point spread function from 1 × 2.1 × 4.7 λ 3 to 1 × 2.2 × 2.1 λ 3. In chicken breast, it differentiated tissue anisotropy and estimated muscle fiber direction. In rabbit cornea, it enabled volumetric shear wave velocity mapping. Conclusion: SE enables 4D shear wave elastography and provides a promising approach for volumetric assessment of tissue biomechanics, anisotropy, and ocular stiffness.