Wang Ping, Zhu He, Kang Hakmook, Gore John C
Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA.
Institute of Imaging Science, Vanderbilt University Medical Center, Nashville, TN, USA; Department of Radiology and Radiological Sciences, Vanderbilt University Medical Center, Nashville, TN, USA.
Magn Reson Imaging. 2017 Oct;42:139-143. doi: 10.1016/j.mri.2017.07.020. Epub 2017 Jul 24.
To evaluate the magnitude of chemical exchange effects and R dispersion in muscle and their relationship to tissue sodium levels with aging.
Seven healthy volunteers (aged 24 to 87years, median age 47) underwent MRI to assess tissue sodium levels and water T values at different spin-locking frequencies in calf muscles. T values at each locking field were computed based on a three-parameter mono-exponential model to fit signals obtained at different locking times, and R (=1/T) rates were compared at different locking fields. In particular, the dispersion of R (ΔR=R(0Hz)-R(500Hz)) was examined as a function of subject age. Muscle sodium content was calculated by comparing signal intensities between tissues and reference standards within the same image. The variations of ΔR with age and sodium were analyzed by linear regression.
T values and sodium content both increased with age. R dispersion also increased with age and showed a strong linear correlation (correlation coefficient r=0.98, P=0.000578) with sodium content.
ΔR reports on the contribution of labile protons such as hydroxyls which may be associated with macromolecule accumulation in the extracellular matrix (ECM). An increase of sodium signal suggests an enlarged ECM volume fraction and/or an increase in sodium concentration, which occurs during normal aging. The strong correlation between ΔR and sodium is likely the consequence of increased ECM and density of total charged sites within the matrix from molecules such as collagens and proteoglycans. The results from this study show the potential use of R dispersion and sodium imaging in the assessment of pathological changes in muscle such as fibrosis.
评估肌肉中化学交换效应和R弥散的程度及其与衰老过程中组织钠水平的关系。
七名健康志愿者（年龄24至87岁，中位年龄47岁）接受了MRI检查，以评估小腿肌肉在不同自旋锁定频率下的组织钠水平和水T值。根据三参数单指数模型计算每个锁定场的T值，以拟合在不同锁定时间获得的信号，并比较不同锁定场的R（=1/T）率。特别是，研究了R的弥散（ΔR = R(0Hz) - R(500Hz)）随受试者年龄的变化。通过比较同一图像中组织与参考标准之间的信号强度来计算肌肉钠含量。通过线性回归分析ΔR随年龄和钠的变化。
T值和钠含量均随年龄增加。R弥散也随年龄增加，并且与钠含量呈现出强线性相关性（相关系数r = 0.98，P = 0.000578）。
ΔR反映了诸如羟基等不稳定质子的贡献，这些质子可能与细胞外基质（ECM）中的大分子积累有关。钠信号的增加表明ECM体积分数增大和/或钠浓度增加，这在正常衰老过程中会发生。ΔR与钠之间的强相关性可能是由于ECM增加以及基质中来自胶原蛋白和蛋白聚糖等分子的总带电位点密度增加的结果。本研究结果表明R弥散和钠成像在评估肌肉病理变化如纤维化方面具有潜在用途。
