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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 effects of varying b-value and TE, on the diffusion-weighted signal from the ocular lens. In the second set of diffusion-weighted experiments (see Materials and Methods), four different b-values within the range of 1300–1600 s/mm2 were each tested with a range of TE from 12 to 30 ms in unidirectional diffusion-weighted scans. The four b-values are represented by the four compartments in the figure above, separated by vertical dashed lines; in each compartment the four TE values tested with the respective b-value are indicated. The colors of the data plots correspond to the six color-coded regions of interest (ROIs) indicated in Figure 5A. Graphs of the mean and standard error of the signal measured in the respective color-coded ROIs are shown for all 16 combinations of b-value and TE. The dashed lines represent exponential curves fitted to estimate the T2 values of various parts of the lens (see Text).
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Figure 7: The effects of varying b-value and TE, on the diffusion-weighted signal from the ocular lens. In the second set of diffusion-weighted experiments (see Materials and Methods), four different b-values within the range of 1300–1600 s/mm2 were each tested with a range of TE from 12 to 30 ms in unidirectional diffusion-weighted scans. The four b-values are represented by the four compartments in the figure above, separated by vertical dashed lines; in each compartment the four TE values tested with the respective b-value are indicated. The colors of the data plots correspond to the six color-coded regions of interest (ROIs) indicated in Figure 5A. Graphs of the mean and standard error of the signal measured in the respective color-coded ROIs are shown for all 16 combinations of b-value and TE. The dashed lines represent exponential curves fitted to estimate the T2 values of various parts of the lens (see Text).

Mentions: The DTI post-processing was done using the open-source 3D Slicer software package (Pieper et al., 2004). Further image post-processing and analysis were performed using custom-written routines in the MATLAB array-oriented scripting language (The MathWorks Inc., Natick, MA, USA). In order to extract values for T2 and D from diffusion-weighted images (see Results; Figures 5 and 7), datasets were fitted with exponential curves (Eq. 1). Curve-fitting was performed using the MATLAB toolbox, EZYFIT (downloaded from http://www.fast.u-psud.fr/ezyfit/). A recursive process using unconstrained non-linear minimization of the sum of squared residuals was used (Moisy, 2009).


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

Vaghefi E, Donaldson PJ - Front Physiol (2013)

The effects of varying b-value and TE, on the diffusion-weighted signal from the ocular lens. In the second set of diffusion-weighted experiments (see Materials and Methods), four different b-values within the range of 1300–1600 s/mm2 were each tested with a range of TE from 12 to 30 ms in unidirectional diffusion-weighted scans. The four b-values are represented by the four compartments in the figure above, separated by vertical dashed lines; in each compartment the four TE values tested with the respective b-value are indicated. The colors of the data plots correspond to the six color-coded regions of interest (ROIs) indicated in Figure 5A. Graphs of the mean and standard error of the signal measured in the respective color-coded ROIs are shown for all 16 combinations of b-value and TE. The dashed lines represent exponential curves fitted to estimate the T2 values of various parts of the lens (see Text).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: The effects of varying b-value and TE, on the diffusion-weighted signal from the ocular lens. In the second set of diffusion-weighted experiments (see Materials and Methods), four different b-values within the range of 1300–1600 s/mm2 were each tested with a range of TE from 12 to 30 ms in unidirectional diffusion-weighted scans. The four b-values are represented by the four compartments in the figure above, separated by vertical dashed lines; in each compartment the four TE values tested with the respective b-value are indicated. The colors of the data plots correspond to the six color-coded regions of interest (ROIs) indicated in Figure 5A. Graphs of the mean and standard error of the signal measured in the respective color-coded ROIs are shown for all 16 combinations of b-value and TE. The dashed lines represent exponential curves fitted to estimate the T2 values of various parts of the lens (see Text).
Mentions: The DTI post-processing was done using the open-source 3D Slicer software package (Pieper et al., 2004). Further image post-processing and analysis were performed using custom-written routines in the MATLAB array-oriented scripting language (The MathWorks Inc., Natick, MA, USA). In order to extract values for T2 and D from diffusion-weighted images (see Results; Figures 5 and 7), datasets were fitted with exponential curves (Eq. 1). Curve-fitting was performed using the MATLAB toolbox, EZYFIT (downloaded from http://www.fast.u-psud.fr/ezyfit/). A recursive process using unconstrained non-linear minimization of the sum of squared residuals was used (Moisy, 2009).

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