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

MRI pulse sequence for diffusion weighting. Diffusion gradients (dark shading) were applied on both sides of the 180° pulse. Here, TE is the echo time; Acq indicates the signal acquisition block. G is the amplitude of the diffusion gradients, δ is their duration and Δ is the delay time between them.
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Figure 2: MRI pulse sequence for diffusion weighting. Diffusion gradients (dark shading) were applied on both sides of the 180° pulse. Here, TE is the echo time; Acq indicates the signal acquisition block. G is the amplitude of the diffusion gradients, δ is their duration and Δ is the delay time between them.

Mentions: To obtain diffusion-weighted images, a bi-polar gradient was added on both sides of the 180° pulse of the spin-echo sequence, as shown in Figure 2. Using this pulse sequence, the amount of signal attenuation is determined by Eq. 1 (Stejskal, 1965; Jones et al., 1999).


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

Vaghefi E, Donaldson PJ - Front Physiol (2013)

MRI pulse sequence for diffusion weighting. Diffusion gradients (dark shading) were applied on both sides of the 180° pulse. Here, TE is the echo time; Acq indicates the signal acquisition block. G is the amplitude of the diffusion gradients, δ is their duration and Δ is the delay time between them.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: MRI pulse sequence for diffusion weighting. Diffusion gradients (dark shading) were applied on both sides of the 180° pulse. Here, TE is the echo time; Acq indicates the signal acquisition block. G is the amplitude of the diffusion gradients, δ is their duration and Δ is the delay time between them.
Mentions: To obtain diffusion-weighted images, a bi-polar gradient was added on both sides of the 180° pulse of the spin-echo sequence, as shown in Figure 2. Using this pulse sequence, the amount of signal attenuation is determined by Eq. 1 (Stejskal, 1965; Jones et al., 1999).

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