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Updated: May 4, 2026
High-resolution Functional Magnetic Resonance Imaging Methods for Human Midbrain
Published on: May 10, 2012
Whole brain mapping of water pools and molecular dynamics with rotating frame MR relaxation using gradient modulated
Ovidiu C Andronesi1, Himanshu Bhat2, Martin Reuter3
1Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
Abstract:
Nuclear magnetic resonance (NMR) relaxation in the rotating frame is sensitive to molecular dynamics on the time scale of water molecules interacting with macromolecules or supramolecular complexes, such as proteins, myelin and cell membranes. Hence, longitudinal (T1ρ) and transverse (T2ρ) relaxation in the rotating frame may have a great potential to probe the macromolecular fraction of tissues. This stimulated a large interest in using this MR contrast to image brain under healthy and disease conditions. However, experimental challenges related to the use of intense radiofrequency irradiation have limited the widespread use of T1ρ and T2ρ imaging. Here, we present methodological development to acquire 3D high-resolution or 2D (multi-)slice selective T1ρ and T2ρ maps of the entire human brain within short acquisition times. These improvements are based on a class of gradient modulated adiabatic pulses that reduce the power deposition, provide slice selection, and mitigate artifacts resulting from inhomogeneities of B1 and B0 magnetic fields. Based on an analytical model of the T1ρ and T2ρ relaxation we compute the maps of macromolecular bound water fraction, correlation and exchange time constants as quantitative biomarkers informative of tissue macromolecular content. Results obtained from simulations, phantoms and five healthy subjects are included.
Insights
This study introduces advanced magnetic resonance imaging (MRI) methods for mapping brain tissue. These techniques overcome previous limitations, enabling faster and more detailed imaging of macromolecular content in the brain.
Area of Science:
- Biophysics
- Magnetic Resonance Imaging
- Neuroscience
Background:
- Nuclear magnetic resonance (NMR) relaxation in the rotating frame is sensitive to molecular dynamics of water interacting with macromolecules.
- Longitudinal (T1ρ) and transverse (T2ρ) relaxation in the rotating frame show potential for probing macromolecular tissue fractions.
- Previous experimental challenges with intense radiofrequency irradiation limited T1ρ and T2ρ imaging.
Purpose of the Study:
- To develop methodological improvements for acquiring 3D high-resolution and 2D T1ρ and T2ρ brain maps.
- To enable rapid acquisition of these maps across the entire human brain.
- To overcome limitations of previous T1ρ and T2ρ imaging techniques.
Main Methods:
- Utilized gradient modulated adiabatic pulses for reduced power deposition, slice selection, and artifact mitigation.
- Developed methods for acquiring 3D high-resolution and 2D (multi-)slice selective T1ρ and T2ρ brain maps.
- Employed an analytical model of T1ρ and T2ρ relaxation to compute quantitative biomarkers.
Main Results:
- Acquired 3D high-resolution and 2D T1ρ and T2ρ maps of the entire human brain within short acquisition times.
- Demonstrated reduced power deposition and artifact mitigation using gradient modulated adiabatic pulses.
- Computed maps of macromolecular bound water fraction, correlation, and exchange time constants.
Conclusions:
- The developed methods enable efficient and high-quality T1ρ and T2ρ mapping of the human brain.
- Quantitative biomarkers derived from T1ρ and T2ρ relaxation provide insights into tissue macromolecular content.
- These advancements facilitate the use of MR imaging for studying brain conditions.
