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

Improvement of fractional anisotropy (FA) maps of the lens as the number of diffusion gradient directions was increased. Grayscale FA maps passing through the visual axis of the lens (see Figures 1B,C) were calculated from eigenvalue maps (Figure 8) based on lens image slices acquired using the four different scanning regimes described in Table 1. Those regimes ranged from 6 to 30 diffusion gradient directions. (A) FA map calculated based on six diffusion gradient directions. (B) FA map based on 12 diffusion gradient directions. (C) 20 directions. (D) 30 directions. The grayscale strip at bottom indicates the FA value range in the images.
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Figure 9: Improvement of fractional anisotropy (FA) maps of the lens as the number of diffusion gradient directions was increased. Grayscale FA maps passing through the visual axis of the lens (see Figures 1B,C) were calculated from eigenvalue maps (Figure 8) based on lens image slices acquired using the four different scanning regimes described in Table 1. Those regimes ranged from 6 to 30 diffusion gradient directions. (A) FA map calculated based on six diffusion gradient directions. (B) FA map based on 12 diffusion gradient directions. (C) 20 directions. (D) 30 directions. The grayscale strip at bottom indicates the FA value range in the images.

Mentions: The performance of the different scanning regimes evaluated in Figure 8, in quantifying anisotropic diffusivity in the lens, was explored by using the eigenvalue maps to calculate maps of FA (Eq. 2; Le Bihan et al., 1992) across the lens (Figure 9).


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

Vaghefi E, Donaldson PJ - Front Physiol (2013)

Improvement of fractional anisotropy (FA) maps of the lens as the number of diffusion gradient directions was increased. Grayscale FA maps passing through the visual axis of the lens (see Figures 1B,C) were calculated from eigenvalue maps (Figure 8) based on lens image slices acquired using the four different scanning regimes described in Table 1. Those regimes ranged from 6 to 30 diffusion gradient directions. (A) FA map calculated based on six diffusion gradient directions. (B) FA map based on 12 diffusion gradient directions. (C) 20 directions. (D) 30 directions. The grayscale strip at bottom indicates the FA value range in the images.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 9: Improvement of fractional anisotropy (FA) maps of the lens as the number of diffusion gradient directions was increased. Grayscale FA maps passing through the visual axis of the lens (see Figures 1B,C) were calculated from eigenvalue maps (Figure 8) based on lens image slices acquired using the four different scanning regimes described in Table 1. Those regimes ranged from 6 to 30 diffusion gradient directions. (A) FA map calculated based on six diffusion gradient directions. (B) FA map based on 12 diffusion gradient directions. (C) 20 directions. (D) 30 directions. The grayscale strip at bottom indicates the FA value range in the images.
Mentions: The performance of the different scanning regimes evaluated in Figure 8, in quantifying anisotropic diffusivity in the lens, was explored by using the eigenvalue maps to calculate maps of FA (Eq. 2; Le Bihan et al., 1992) across the lens (Figure 9).

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