Acoustic Radiation Force Optical Coherence Elastography of the Crystalline Lens: Safety

Purpose: To assess the safety of acoustic radiation force optical coherence elastography in the crystalline lens in situ. Methods: Acoustic radiation force (ARF) produced by an immersion single-element ultrasound transducer (nominal frequency = 3.5 MHz) was characterized using a needle hydrophone and used for optical coherence elastography (OCE) of the crystalline lens. Preamplified signals at 50, 100, 250, 500, 750, 1000, and 1250 mV peak amplitude were tested on ex vivo porcine eyes (n = 21). Three-dimensional optical coherence tomography (OCT) and confocal microscopy images were acquired before and after ARF exposure to each signal amplitude to determine damage. Results: The acoustic intensity of the ultrasound transducer at 100-mV preamplified peak amplitude input demonstrated a signal-to-noise ratio high enough for tracking elastic wave propagation in the lens and spatial-peak pulse-average (SPPA) intensity of 24.1 W/cm(2) and mechanical index (MI) of 0.46. The SPPA intensity was lower than the U.S. Food and Drug Administration (FDA) safety limit (28 W/cm(2)), but the MI was twice the safety limit (0.23). OCT structural and confocal microscopy images showed damage only at levels exceeding 1150 W/cm(2) and 3.2 for SPPA intensity and MI, respectively. Conclusions: OCT and confocal microscopy showed that, even when the intensity exceeded FDA recommendations (>100 mV), no noticeable damage was observed. Although a further reduction in acoustic intensity is necessary to meet FDA safety limits, ARF-based elastography shows promise for safe clinical translation in quantitatively characterizing lenticular biomechanical properties. Translational Relevance: This work assessed the safety standards for acoustic radiation force to be used in human lens elastography according to the FDA safety limits.