Abstract
We describe our development of the diffusion tensor imaging modality for the bovine ocular lens. Diffusion gradients were added to a spin-echo pulse sequence and the relevant parameters of the sequence were refined to achieve good diffusion weighting in the lens tissue, which demonstrated heterogeneous regions of diffusive signal attenuation. Decay curves for b-value (loosely summarizes the strength of diffusion weighting) and TE (determines the amount of magnetic resonance imaging-obtained signal) were used to estimate apparent diffusion coefficients (ADC) and T2 in different lens regions. The ADCs varied by over an order of magnitude and revealed diffusive anisotropy in the lens. Up to 30 diffusion gradient directions, and 8 signal acquisition averages, were applied to lenses in culture in order to improve maps of diffusion tensor eigenvalues, equivalent to ADC, across the lens. From these maps, fractional anisotropy maps were calculated and compared to known spatial distributions of anisotropic molecular fluxes in the lens. This comparison suggested new hypotheses and experiments to quantitatively assess models of circulation in the avascular lens.
Highlights
The ocular lens appears deceptively simple: like a transparent glass element of an engineered optical device such as a camera lens
Here we have reported our development of the diffusion tensor imaging (DTI) modality for the ocular lens
Various studies have demonstrated the potential of diffusion-weighted magnetic resonance imaging (MRI) for studying the whole eye (De Potter et al, 1995; Ettl et al, 2000) or the ocular lens (Racz et al, 1983; Ahn et al, 1989; Lizak et al, 2000)
Summary
The ocular lens appears deceptively simple: like a transparent glass element of an engineered optical device such as a camera lens. Lens transparency must be constantly upheld by homeostasis within the tissue; but it requires an absence of blood vessels in the light path (Mathias et al, 1981; Baldo and Mathias, 1992) This paradox of homeostasis in the absence of blood circulation appears to be solved in the lens by an avascular micro-circulation system, capable of supplying oxygen and nutrients throughout the lentoid mass of cells, via cell membrane pumps, transporters and channels, and extracellular circulatory routes (Mathias et al, 1997, 2010). While this variety of studies has made great progress toward understanding the biophysical basis of ocular lens circulation and transparency, there remains a need for direct, non-invasive study of micro-circulation in the unperturbed lens, and for interrogation deep within the lens tissue
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