Abstract
Objective
Multi-component T2 relaxation allows for assessing the myelin water fraction in nervous tissue, providing a surrogate marker for demyelination. The assessment of the number and distribution of different T2 components for devising exact models of tissue relaxation has been limited by T2 sampling with conventional MR methods.
Materials and methods
A T2-prepared UTE sequence was used to assess multicomponent T2 relaxation at 9.4 T of fixed mouse and rat spinal cord samples and of mouse spinal cord in vivo. For in vivo scans, a cryogenically cooled probe allowed for 78-µm resolution in 1-mm slices. Voxel-wise non-negative least square analysis was used to assess the number of myelin water-associated T2 components.
Results
More than one myelin water-associated T2 component was detected in only 12 % of analyzed voxels in rat spinal cords and 6 % in mouse spinal cords, both in vivo and in vitro. However, myelin water-associated T2 values of individual voxels varied between 0.1 and 20 ms. While in fixed samples almost no components below 1 ms were identified, in vivo, these contributed 14 % of the T2 spectrum. No significant differences in MWF were observed in mouse spinal cord in vivo versus ex vivo measurements.
Conclusion
Voxel-wise analysis methods using relaxation models with one myelin water-associated T2 component are appropriate for assessing myelin content of nervous tissue.
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Abbreviations
- CPMG:
-
Carr-Purcell-Meiboom-Gill
- CSF:
-
Cerebrospinal fluid
- FWF:
-
Free water fraction
- GM:
-
Gray matter
- IE:
-
Intra-/extracellular
- MET2:
-
Multi-exponential T2
- MRI:
-
Magnetic resonance imaging
- MWF:
-
Myelin water fraction
- NNLS:
-
Non-negative least square
- OWF:
-
Other water fraction
- PBS:
-
Phosphate-buffered saline
- ROI:
-
Region of interest
- SNR:
-
Signal-to-noise ratio
- TE:
-
Echo time
- TR:
-
Repetition time
- UTE:
-
Ultrashort echo time
- WM:
-
White matter
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Acknowledgments
This work was supported by the German Research Foundation SFB 1009 Project Z02 and the IZKF Münster, PIX. We thank Nathalie Just and Lydia Wachsmuth for helpful comments.
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All procedures performed in studies involving animals were in accordance with national legislation and in accordance with the ethical standards in North Rhine Westphalia. This article does not contain any studies with human participants performed by any of the authors.
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Klasen, T., Faber, C. Assessment of the myelin water fraction in rodent spinal cord using T2-prepared ultrashort echo time MRI. Magn Reson Mater Phy 29, 875–884 (2016). https://doi.org/10.1007/s10334-016-0579-7
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DOI: https://doi.org/10.1007/s10334-016-0579-7