van Gelderen Peter, Wang Yicun, de Zwart Jacco A, Duyn Jeff H
Advanced MRI Section, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland, USA.
Magn Reson Med. 2025 May;93(5):2140-2152. doi: 10.1002/mrm.30400. Epub 2024 Dec 17.
To quantify T relaxation in the brain at 3 T and 7 T to study its field dependence and correlation with iron content, and to investigate whether iron can be separated from other sources of T relaxation based on this field dependence.
Nine subjects were scanned at both field strengths with the same acquisition technique, which used multiple gradient-echo sampling of a spin echo. This allowed for separation of T relaxation from static dephasing by B field inhomogeneities and the effects of radiofrequency refocusing imperfections. The average relaxation rates (R = 1/T) in multiple regions of interest in the brain were fitted with a model linear in B and correlated with literature iron values.
The relationship between the R values at the two field strengths appeared to be linear over all regions of interest. The R values (in s) in the regions of interest for which both an iron and a lipid mass fraction have been documented in the literature were fitted as , where and indicate the putative mass fractions of iron and lipid.
The R relaxation rate is well described by a constant plus a term linear in B, with both iron and lipid content contributing to the slope. This indicates that the contributions of lipid and iron to R cannot be separated based solely on the field dependence of R in the field range of 3-7 T.
在3 T和7 T场强下对大脑中的T弛豫进行定量分析，以研究其场强依赖性及其与铁含量的相关性，并基于这种场强依赖性研究铁是否能与其他T弛豫源区分开来。
对9名受试者在两种场强下采用相同的采集技术进行扫描，该技术使用自旋回波的多次梯度回波采样。这使得能够将T弛豫与由B场不均匀性引起的静态去相位以及射频重聚焦不完善的影响区分开来。对大脑多个感兴趣区域的平均弛豫率（R = 1/T）采用B的线性模型进行拟合，并与文献中的铁含量值相关联。
在所有感兴趣区域，两种场强下的R值之间的关系似乎呈线性。文献中已记录铁和脂质质量分数的感兴趣区域的R值（单位为s）拟合为 ，其中 和 分别表示推测的铁和脂质的质量分数。
R弛豫率可以很好地用一个常数加上一个与B呈线性关系的项来描述，铁和脂质含量都对斜率有贡献。这表明在3 - 7 T的场强范围内，仅基于R的场强依赖性无法区分脂质和铁对R的贡献。
