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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, on the diffusion-weighted signal from the ocular lens. (A) Six regions of interest (ROIs; yellow dashed lines) were selected in lens image slices from unidirectional diffusion-weighted scans (Figure 4). The direction of the diffusion gradients was from bottom-left to top-right in the plane of the images. The letter inside each ROI stands for the color of the corresponding signal plot in (B), namely cyan (C), red (R), pink (P), green (G), blue (B), and black (K). Note, ROIs G and R sample areas where the direction of the diffusion gradients runs predominantly radially in the lens tissue (see Figure 1C); in contrast, ROIs B and C sample areas where the direction of the diffusion gradients runs more tangentially to the lens curvature. (B) Graphs of the mean and standard error of the signal measured in the respective color-coded ROIs for eight different b-values. The dashed lines represent exponential curves fitted to estimate the diffusion coefficients (labeled D near each curve) in the ROIs with respect to the applied diffusion gradient. The values for D are given in 10−3 mm2/s. The TE in these experiments was 12 ms.
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Figure 5: The effects of varying b-value, on the diffusion-weighted signal from the ocular lens. (A) Six regions of interest (ROIs; yellow dashed lines) were selected in lens image slices from unidirectional diffusion-weighted scans (Figure 4). The direction of the diffusion gradients was from bottom-left to top-right in the plane of the images. The letter inside each ROI stands for the color of the corresponding signal plot in (B), namely cyan (C), red (R), pink (P), green (G), blue (B), and black (K). Note, ROIs G and R sample areas where the direction of the diffusion gradients runs predominantly radially in the lens tissue (see Figure 1C); in contrast, ROIs B and C sample areas where the direction of the diffusion gradients runs more tangentially to the lens curvature. (B) Graphs of the mean and standard error of the signal measured in the respective color-coded ROIs for eight different b-values. The dashed lines represent exponential curves fitted to estimate the diffusion coefficients (labeled D near each curve) in the ROIs with respect to the applied diffusion gradient. The values for D are given in 10−3 mm2/s. The TE in these experiments was 12 ms.

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, on the diffusion-weighted signal from the ocular lens. (A) Six regions of interest (ROIs; yellow dashed lines) were selected in lens image slices from unidirectional diffusion-weighted scans (Figure 4). The direction of the diffusion gradients was from bottom-left to top-right in the plane of the images. The letter inside each ROI stands for the color of the corresponding signal plot in (B), namely cyan (C), red (R), pink (P), green (G), blue (B), and black (K). Note, ROIs G and R sample areas where the direction of the diffusion gradients runs predominantly radially in the lens tissue (see Figure 1C); in contrast, ROIs B and C sample areas where the direction of the diffusion gradients runs more tangentially to the lens curvature. (B) Graphs of the mean and standard error of the signal measured in the respective color-coded ROIs for eight different b-values. The dashed lines represent exponential curves fitted to estimate the diffusion coefficients (labeled D near each curve) in the ROIs with respect to the applied diffusion gradient. The values for D are given in 10−3 mm2/s. The TE in these experiments was 12 ms.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 5: The effects of varying b-value, on the diffusion-weighted signal from the ocular lens. (A) Six regions of interest (ROIs; yellow dashed lines) were selected in lens image slices from unidirectional diffusion-weighted scans (Figure 4). The direction of the diffusion gradients was from bottom-left to top-right in the plane of the images. The letter inside each ROI stands for the color of the corresponding signal plot in (B), namely cyan (C), red (R), pink (P), green (G), blue (B), and black (K). Note, ROIs G and R sample areas where the direction of the diffusion gradients runs predominantly radially in the lens tissue (see Figure 1C); in contrast, ROIs B and C sample areas where the direction of the diffusion gradients runs more tangentially to the lens curvature. (B) Graphs of the mean and standard error of the signal measured in the respective color-coded ROIs for eight different b-values. The dashed lines represent exponential curves fitted to estimate the diffusion coefficients (labeled D near each curve) in the ROIs with respect to the applied diffusion gradient. The values for D are given in 10−3 mm2/s. The TE in these experiments was 12 ms.
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