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Updated: Sep 13, 2025
High-resolution Functional Magnetic Resonance Imaging Methods for Human Midbrain
Published on: May 10, 2012
Fiber orientation-dependent T1 angular features in human white matter at 1.5 T, 3 T, and 7 T
Risto A Kauppinen1, Ekaterina Paasonen2,3, Jeromy Thotland4
1Department of Electric, Electronic and Mechanical Engineering, University of Bristol, Bristol, UK.
Purpose:
White matter (WM) microstructure influences T1 in vivo. Here, T1 angular features were studied in human WM in vivo in quantitative terms at 1.5 T, 3 T and 7 T.
Methods:
MP2RAGE MRI was used to compute absolute T1 images of the brain at three fields. Diffusion MRI images were acquired using the manufacturer's diffusion MRI (dMRI) protocol at 1.5 T and Human Connectome Project protocols at 3 T and 7 T to compute WM microstructural DTI indices. Axonal fiber-to-field dependency of T1 relaxation was determined in WM and the quantitative characteristics of the angular features were measured in absolute terms at all three fields.
Results:
Two angular features in T1 relaxation were present in WM with fractional anisotropy >0.5 at all three fields showing the characteristics: (1) increasing T1 relaxation from parallel to perpendicular orientations of axonal fibers and (2) a broad long T1 hump centered around 40° orientation in respect to the field. The former feature amounted to 4.5% to 4.9% of average T1 at three fields, the latter was 4.2% to 3.4% of average T1 at 1.5 T and 3 T, but only to 1.8% at 7 T. The angular plots of signals in TI images indicated much shorter T1 in the proton species underpinning the 40° feature at 1.5 T than at 7 T, which may underpin the quantitative difference of the 40° hump between the fields.
Conclusions:
T1 relaxation anisotropy is an inherent WM MRI contrast that is detectable at all MR fields most commonly used in human neuroimaging, and it should be considered in the evaluations of quantitative T1 MRI.
Insights
White matter T1 relaxation shows angular features related to axonal fiber orientation across multiple magnetic field strengths. This inherent MRI contrast is detectable in vivo and crucial for quantitative T1 imaging analysis.
Area of Science:
- Neuroimaging
- Biophysics
- Magnetic Resonance Imaging
Background:
- White matter microstructure significantly impacts T1 relaxation times in vivo.
- Understanding T1 angular features is essential for accurate quantitative MRI analysis.
Purpose of the Study:
- To quantitatively investigate T1 angular features in human white matter in vivo.
- To assess these features across different magnetic field strengths (1.5T, 3T, and 7T).
Main Methods:
- MP2RAGE MRI sequences were used to acquire absolute T1-weighted images.
- Diffusion MRI (dMRI) was employed to calculate white matter microstructural indices.
- The fiber-to-field dependency of T1 relaxation was analyzed quantitatively.
Main Results:
- Two distinct T1 relaxation angular features were observed in white matter (FA > 0.5) at all field strengths.
- These features include increasing T1 from parallel to perpendicular fiber orientations and a T1 hump around 40°.
- The magnitude of the 40° hump varied with field strength, suggesting differences in underlying proton species T1.
Conclusions:
- T1 relaxation anisotropy is an intrinsic contrast in white matter detectable across common human neuroimaging field strengths.
- This anisotropy must be considered for accurate quantitative T1 MRI evaluations.
- The findings highlight the importance of accounting for microstructural orientation in T1 relaxometry.
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