Development of a multi-parametric MRI platform to evaluate steady-state water content and optical properties in...

Here we describe the development of magnetic resonance imaging (MRI) protocols which when run on a standard clinical 3T MRI system can non-invasively monitor changes in the water content and refractive properties of bovine lenses maintained under organ culture. Fresh bovine lenses were incubated in artificial aqueous humour and placed in a custom holder within a hand/wrist coil. Multi-parametric mapping sequences (T1, T2∗, proton density [PD], and magnetisation transfer [MT] ratio) were optimised to quantify the total, free, and bound water compartments in distinct lens regions (outer cortex, inner cortex, and nucleus). Repeated scanning on different days demonstrated robust inter-sample reproducibility. MRI-derived T2∗ and MT ratio values were calibrated against refractive index (n) profiles calculated using laser ray tracing and subsequently applied to ZEMAX optical modelling to calculate lens power. The imaging protocol achieved high spatial resolution and reproducibility, which allowed the detection of regional variations in water composition within a practical scan time. Hypotonic lens swelling induced significant increases in total and free water across all lens regions but had no effect on bound water or the refractive index gradient. Lens swelling increased lens power (ΔP = 2.98D, p = 0.04) primarily due to a change in the surface geometry of the lens. This ability to quantify lens water states and refractive changes across multiple lens samples will facilitate the screening of novel pharmacological reagents that modulate lens water transport, allowing for testing of their efficacy as potential anti-cataract therapies.