Zhao Zhenkai, Smith Fiona Elizabeth, Dick Taylor J M, Hodson-Tole Emma
Department of Life Sciences, Manchester Metropolitan University, Manchester, United Kingdom.
Manchester Institute of Sport, Manchester Metropolitan University, Manchester, United Kingdom.
Front Bioeng Biotechnol. 2025 Jun 2;13:1594557. doi: 10.3389/fbioe.2025.1594557. eCollection 2025.
Accumulation of intramuscular fat (IMF) is an important marker of skeletal muscle health, typically reported as the mean intramuscular fat fraction (FF) from quantitative magnetic resonance imaging (MRI). However, such a summary measure does not reveal the spatial distribution of the FF through the muscle volume, and currently no methods to quantify intramuscular FF spatial distribution have been reported. This study assessed two- and three-dimensional characteristics of intramuscular FF spatial distribution and investigated age-related differences in intramuscular FF clustering in medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (SOL) muscles.
A total of 32 physically active young ( = 19, 23.8 ± 2.2 years) and older ( = 13, 70.1 ± 2.2 years) participants were recruited. Intramuscular FF regions were extracted from axial mDixon MRIs using a region-growing method, revealing branch-like clusters, potentially following the vasculature. Three-dimensional intramuscular FF clustering and density were assessed using Delaunay tessellation and Ripley's functions.
Older adults exhibited significantly shorter Delaunay mean edge lengths compared to young (MG: 2.6 ± 0.5 mm vs. 3.2±0.4 mm, < 0.001; LG: 2.5 ± 0.6 mm vs. 3.3 ± 0.8 mm, < 0.001; SOL: 2.4 ± 0.4 mm vs. 3.5 ± 0.7 mm, < 0.001), indicating denser clustering. Ripley's K function confirmed greater clustering in older adults. Two-way ANOVA revealed aging (F statistics = 21, < 0.001, Hedge's = 1.8) but not sex (F statistics = 1.5, = 0.9, Hedge's = 0.3) as the main effect for variation in intramuscular FF clustering, with no interaction between these two factors (F statistics = 1.3, = 0.35).
This work provides an objective framework for characterizing intramuscular FF spatial distribution, providing a means to track skeletal muscle fatty replacement and provide more robust and sensitive markers of skeletal muscle health.
肌内脂肪（IMF）的积累是骨骼肌健康的重要标志，通常通过定量磁共振成像（MRI）报告为平均肌内脂肪分数（FF）。然而，这种汇总测量方法并未揭示FF在肌肉体积中的空间分布，目前尚无量化肌内FF空间分布的方法报道。本研究评估了肌内FF空间分布的二维和三维特征，并研究了比目鱼肌内侧（MG）、比目鱼肌外侧（LG）和比目鱼肌（SOL）中肌内FF聚集的年龄相关差异。
共招募了32名身体活跃的年轻人（n = 19，23.8±2.2岁）和老年人（n = 13，70.1±2.2岁）参与者。使用区域生长法从轴向mDixon MRI中提取肌内FF区域，显示出分支状簇，可能沿着血管分布。使用Delaunay三角剖分和Ripley函数评估三维肌内FF聚集和密度。
与年轻人相比，老年人的Delaunay平均边长明显更短（MG：2.6±0.5 mm对3.2±0.4 mm，P < 0.001；LG：2.5±0.6 mm对3.3±0.8 mm，P < 0.001；SOL：2.4±0.4 mm对3.5±0.7 mm，P < 0.001），表明聚集更密集。Ripley's K函数证实老年人的聚集程度更高。双向方差分析显示，衰老（F统计量 = 21，P < 0.001，Hedge's g = 1.8）而非性别（F统计量 = 1.5，P = 0.9，Hedge's g = 0.3）是肌内FF聚集变化的主要影响因素，这两个因素之间没有相互作用（F统计量 = 1.3，P = 0.35）。
这项工作为表征肌内FF空间分布提供了一个客观框架，为追踪骨骼肌脂肪替代提供了一种方法，并为骨骼肌健康提供了更可靠和敏感的标志物。
