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An exploration into diffusion tensor imaging in the bovine ocular lens.

Vaghefi E, Donaldson PJ - Front Physiol (2013)

Bottom Line: 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.This comparison suggested new hypotheses and experiments to quantitatively assess models of circulation in the avascular lens.

View Article: PubMed Central - PubMed

Affiliation: Auckland Bioengineering Institute, University of Auckland Auckland, New Zealand ; Department of Optometry and Vision Sciences, University of Auckland Auckland, New Zealand.

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.

No MeSH data available.


Related in: MedlinePlus

The ocular lens. (A) A clear crystalline rat lens with visual axis oriented toward the viewer. Scale bar, 1 mm. (B) A simplified diagram of the lens cellular structure showing anterior and posterior poles; inner, elongated fiber cells; and an outer layer of cuboidal epithelial cells over the anterior side of the lens. Fiber cell nuclei degrade as the cells age (toward the lens center). Arrows label directions within the lens as follows: r, radial; c, circumferential; z, visual axis. Reproduced with permission from Jacobs et al. (2004). (C) The 2D schematic of the lens axial cut with the anterior and posterior poles marked and the zigzag sutures connecting the poles illustrated. The center-located arrow demonstrates the direction of the applied excitation gradient, which is in parallel with the cortical fiber cell directions in upper-left and lower-right regions. At the same time it is perpendicular to the fiber cell extrusion direction in the upper right and lower left sections.
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Figure 1: The ocular lens. (A) A clear crystalline rat lens with visual axis oriented toward the viewer. Scale bar, 1 mm. (B) A simplified diagram of the lens cellular structure showing anterior and posterior poles; inner, elongated fiber cells; and an outer layer of cuboidal epithelial cells over the anterior side of the lens. Fiber cell nuclei degrade as the cells age (toward the lens center). Arrows label directions within the lens as follows: r, radial; c, circumferential; z, visual axis. Reproduced with permission from Jacobs et al. (2004). (C) The 2D schematic of the lens axial cut with the anterior and posterior poles marked and the zigzag sutures connecting the poles illustrated. The center-located arrow demonstrates the direction of the applied excitation gradient, which is in parallel with the cortical fiber cell directions in upper-left and lower-right regions. At the same time it is perpendicular to the fiber cell extrusion direction in the upper right and lower left sections.

Mentions: The ocular lens appears deceptively simple: like a transparent glass element of an engineered optical device such as a camera lens. In reality, the ocular lens is a complex assembly, mainly of elongated fiber cells which confer transparency and allow focal accommodation, by maintaining tightly controlled cellular biochemistry, volume regulation, and structural integrity (Figure 1; Koretz and Handelman, 1983; Pierscionek and Chan, 1989; Donaldson et al., 2001; Kuszak et al., 2006; Davidovits, 2008).


An exploration into diffusion tensor imaging in the bovine ocular lens.

Vaghefi E, Donaldson PJ - Front Physiol (2013)

The ocular lens. (A) A clear crystalline rat lens with visual axis oriented toward the viewer. Scale bar, 1 mm. (B) A simplified diagram of the lens cellular structure showing anterior and posterior poles; inner, elongated fiber cells; and an outer layer of cuboidal epithelial cells over the anterior side of the lens. Fiber cell nuclei degrade as the cells age (toward the lens center). Arrows label directions within the lens as follows: r, radial; c, circumferential; z, visual axis. Reproduced with permission from Jacobs et al. (2004). (C) The 2D schematic of the lens axial cut with the anterior and posterior poles marked and the zigzag sutures connecting the poles illustrated. The center-located arrow demonstrates the direction of the applied excitation gradient, which is in parallel with the cortical fiber cell directions in upper-left and lower-right regions. At the same time it is perpendicular to the fiber cell extrusion direction in the upper right and lower left sections.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3585442&req=5

Figure 1: The ocular lens. (A) A clear crystalline rat lens with visual axis oriented toward the viewer. Scale bar, 1 mm. (B) A simplified diagram of the lens cellular structure showing anterior and posterior poles; inner, elongated fiber cells; and an outer layer of cuboidal epithelial cells over the anterior side of the lens. Fiber cell nuclei degrade as the cells age (toward the lens center). Arrows label directions within the lens as follows: r, radial; c, circumferential; z, visual axis. Reproduced with permission from Jacobs et al. (2004). (C) The 2D schematic of the lens axial cut with the anterior and posterior poles marked and the zigzag sutures connecting the poles illustrated. The center-located arrow demonstrates the direction of the applied excitation gradient, which is in parallel with the cortical fiber cell directions in upper-left and lower-right regions. At the same time it is perpendicular to the fiber cell extrusion direction in the upper right and lower left sections.
Mentions: The ocular lens appears deceptively simple: like a transparent glass element of an engineered optical device such as a camera lens. In reality, the ocular lens is a complex assembly, mainly of elongated fiber cells which confer transparency and allow focal accommodation, by maintaining tightly controlled cellular biochemistry, volume regulation, and structural integrity (Figure 1; Koretz and Handelman, 1983; Pierscionek and Chan, 1989; Donaldson et al., 2001; Kuszak et al., 2006; Davidovits, 2008).

Bottom Line: 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.This comparison suggested new hypotheses and experiments to quantitatively assess models of circulation in the avascular lens.

View Article: PubMed Central - PubMed

Affiliation: Auckland Bioengineering Institute, University of Auckland Auckland, New Zealand ; Department of Optometry and Vision Sciences, University of Auckland Auckland, New Zealand.

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.

No MeSH data available.


Related in: MedlinePlus