Limits...
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

T2 gray-scale image of the bovine lens. The lightest area has the longest T2 values and the darkest area has the shortest T2 values.
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Figure 3: T2 gray-scale image of the bovine lens. The lightest area has the longest T2 values and the darkest area has the shortest T2 values.

Mentions: As an initial step, we acquired T2-weighted images of the lens using a spin-echo sequence, to evaluate the signal behavior without any diffusion weighting. As the T2 relaxation times of the ocular lens are known to be relatively short (Patz et al., 2007), the short TE used here (12 ms) was deemed appropriate for T2 weighting. A T2-weighted image of the bovine lens, acquired using our protocol, is shown in Figure 3. The lens was clearly visible, with the shading increasingly dark toward the lens center as a result of shorter T2 values. This decrease in T2 within the lens was consistent with data from the literature (Cheng et al., 1987; Moffat and Pope, 2002b) indicating increasing protein concentration toward the center of the ocular lens.


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

Vaghefi E, Donaldson PJ - Front Physiol (2013)

T2 gray-scale image of the bovine lens. The lightest area has the longest T2 values and the darkest area has the shortest T2 values.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: T2 gray-scale image of the bovine lens. The lightest area has the longest T2 values and the darkest area has the shortest T2 values.
Mentions: As an initial step, we acquired T2-weighted images of the lens using a spin-echo sequence, to evaluate the signal behavior without any diffusion weighting. As the T2 relaxation times of the ocular lens are known to be relatively short (Patz et al., 2007), the short TE used here (12 ms) was deemed appropriate for T2 weighting. A T2-weighted image of the bovine lens, acquired using our protocol, is shown in Figure 3. The lens was clearly visible, with the shading increasingly dark toward the lens center as a result of shorter T2 values. This decrease in T2 within the lens was consistent with data from the literature (Cheng et al., 1987; Moffat and Pope, 2002b) indicating increasing protein concentration toward the center of the ocular lens.

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