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Single-point macromolecular proton fraction mapping using a 0.3 T permanent magnet MRI system: phantom and healthy
Yasuhiro Fujiwara1, Shoma Eitoku2, Nobutaka Sakae3
1Department of Medical Imaging Technology, Faculty of Life Sciences, Kumamoto University, 4-24-1, Kuhonji, Chuo-Ku, Kumamoto, 862-0976, Japan. yfuji@kumamoto-u.ac.jp.
Abstract:
In a 0.3 T permanent-magnet magnetic resonance imaging (MRI) system, quantifying myelin content is challenging owing to long imaging times and low signal-to-noise ratio. macromolecular proton fraction (MPF) offers a quantitative assessment of myelin in the nervous system. We aimed to demonstrate the practical feasibility of MPF mapping in the brain using a 0.3 T MRI. Both 0.3 T and 3.0 T MRI systems were used. The MPF-mapping protocol used a standard 3D fast spoiled gradient-echo sequence based on the single-point reference method. Proton density, T1, and magnetization transfer-weighted images were obtained from a protein phantom at 0.3 T and 3.0 T to calculate MPF maps. MPF was measured in all phantom sections to assess its relationship to protein concentration. We acquired MPF maps for 16 and 8 healthy individuals at 0.3 T and 3.0 T, respectively, measuring MPF in nine brain tissues. Differences in MPF between 0.3 T and 3.0 T, and between 0.3 T and previously reported MPF at 0.5 T, were investigated. Pearson's correlation coefficient between protein concentration and MPF at 0.3 T and 3.0 T was 0.92 and 0.90, respectively. The 0.3 T MPF of brain tissue strongly correlated with 3.0 T MPF and literature values measured at 0.5 T. The absolute mean differences in MPF between 0.3 T and 0.5 T were 0.42% and 1.70% in white and gray matter, respectively. Single-point MPF mapping using 0.3 T permanent-magnet MRI can effectively assess myelin content in neural tissue.
Insights
Quantifying myelin content using macromolecular proton fraction (MPF) mapping is feasible with 0.3 Tesla MRI. This method provides accurate myelin assessment in neural tissue, correlating well with higher field strengths.
Area of Science:
- Neuroimaging
- Biophysics
- Quantitative MRI
Background:
- Assessing myelin content is crucial for understanding neurological disorders.
- Low-field MRI (0.3 Tesla) presents challenges in myelin quantification due to low signal-to-noise ratio and long scan times.
- Macromolecular proton fraction (MPF) mapping offers a quantitative approach to myelin assessment.
Purpose of the Study:
- To demonstrate the practical feasibility of MPF mapping in the brain using a low-field 0.3 Tesla MRI system.
- To evaluate the accuracy and reliability of MPF measurements at 0.3 Tesla compared to higher field strengths (3.0 Tesla) and literature values.
- To assess the correlation between MPF and protein concentration in phantoms at 0.3 Tesla.
Main Methods:
- MPF mapping protocol utilizing a 3D fast spoiled gradient-echo sequence with a single-point reference method.
- Acquisition of proton density, T1, and magnetization transfer-weighted images at both 0.3 Tesla and 3.0 Tesla.
- Measurement of MPF in a protein phantom and in nine brain tissues of healthy individuals at both field strengths.
Main Results:
- High correlation (Pearson's r = 0.92 at 0.3T, 0.90 at 3.0T) between MPF and protein concentration in phantoms.
- Strong correlation between MPF values obtained at 0.3 Tesla and those measured at 3.0 Tesla and previously reported at 0.5 Tesla.
- Small absolute mean differences in MPF between 0.3 Tesla and 0.5 Tesla (0.42% in white matter, 1.70% in gray matter).
Conclusions:
- Single-point MPF mapping is a practical and effective method for assessing myelin content in neural tissue using low-field 0.3 Tesla permanent-magnet MRI.
- The findings support the use of low-field MRI systems for quantitative myelin assessment, enhancing accessibility.
- MPF mapping at 0.3 Tesla provides reliable and comparable results to higher field strengths.
