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

Ocular lens imaged using diffusion weighting pulse sequences with combinations of different b-values and TEs. In the second set of diffusion-weighted experiments (see Materials and Methods), b-values within the range of 1300–1600 s/mm2 were tested with a range of TE from 12 to 30 ms in unidirectional diffusion-weighted scans. For the combinations tested, there was a pronounced, general loss of signal as TE was increased; as well as attenuation as b-value was increased, consistent with the results shown earlier. The lens, image slice and diffusion gradients were oriented as in Figures 4 and 5.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3585442&req=5

Figure 6: Ocular lens imaged using diffusion weighting pulse sequences with combinations of different b-values and TEs. In the second set of diffusion-weighted experiments (see Materials and Methods), b-values within the range of 1300–1600 s/mm2 were tested with a range of TE from 12 to 30 ms in unidirectional diffusion-weighted scans. For the combinations tested, there was a pronounced, general loss of signal as TE was increased; as well as attenuation as b-value was increased, consistent with the results shown earlier. The lens, image slice and diffusion gradients were oriented as in Figures 4 and 5.

Mentions: In the second set of diffusion-weighted experiments, we tested the use of longer TE values ranging up to 30 ms, at each of four different b-values selected from the 1300–1600 s/mm2 range that was indicated in the first set of experiments. In total, 16 combinations of TE and b-value were tested (Figure 6). It was apparent from the images that as TE was increased there was a pronounced general loss of signal; and that signal was also increasingly attenuated as b-value was increased.


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

Vaghefi E, Donaldson PJ - Front Physiol (2013)

Ocular lens imaged using diffusion weighting pulse sequences with combinations of different b-values and TEs. In the second set of diffusion-weighted experiments (see Materials and Methods), b-values within the range of 1300–1600 s/mm2 were tested with a range of TE from 12 to 30 ms in unidirectional diffusion-weighted scans. For the combinations tested, there was a pronounced, general loss of signal as TE was increased; as well as attenuation as b-value was increased, consistent with the results shown earlier. The lens, image slice and diffusion gradients were oriented as in Figures 4 and 5.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 6: Ocular lens imaged using diffusion weighting pulse sequences with combinations of different b-values and TEs. In the second set of diffusion-weighted experiments (see Materials and Methods), b-values within the range of 1300–1600 s/mm2 were tested with a range of TE from 12 to 30 ms in unidirectional diffusion-weighted scans. For the combinations tested, there was a pronounced, general loss of signal as TE was increased; as well as attenuation as b-value was increased, consistent with the results shown earlier. The lens, image slice and diffusion gradients were oriented as in Figures 4 and 5.
Mentions: In the second set of diffusion-weighted experiments, we tested the use of longer TE values ranging up to 30 ms, at each of four different b-values selected from the 1300–1600 s/mm2 range that was indicated in the first set of experiments. In total, 16 combinations of TE and b-value were tested (Figure 6). It was apparent from the images that as TE was increased there was a pronounced general loss of signal; and that signal was also increasingly attenuated as b-value was increased.

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