Characterization of the regional distribution of skeletal muscle adipose tissue in type 2 diabetes using chemical shift-based water/fat separation

Abstract

Purpose: To show the feasibility of assessing the spatial distribution of skeletal muscle adipose tissue using chemical shift-based water/fat separation and to characterize differences in calf intermuscular adipose tissue (IMAT) compartmentalization in patients with type 2 diabetes mellitus (T2DM) compared to healthy age-matched controls.

Materials and methods: A chemical shift-based water/fat separation approach using a multiecho 3D spoiled gradient echo sequence was applied in a study of 64 patients, including 35 healthy controls and 29 subjects with T2DM. Masks were defined based on manual segmentations to compute fat volume within different compartments, including regions of subcutaneous adipose tissue (SAT) and six muscular regions. IMAT was divided into two compartments representing fat within the muscular regions (intraMF) and fat between the muscular regions (interMF). Two-sample Student's t-tests were used to compare fat volumes between the two groups.

Results: The subjects with T2DM had a lower volume of SAT compared to the healthy controls (P = 4 × 10(-5) ). There was no statistically significant difference in the IMAT volume between the two groups. However, the intraMF volume normalized by the IMAT volume was higher in the diabetics compared to the controls (P = 0.006).

Conclusion: Chemical shift-based water/fat separation enables the quantification of fat volume within localized muscle regions, showing that the IMAT regional distribution is significantly different in T2DM compared to normal controls.

Figure 1

Segmentation of muscle and fat compartments: (a) typical in-phase IDEAL image and superimposed ROIs for subcutaneous fat and bone and bone marrow regions, (b) subcutaneous adipose tissue (SAT) mask, (c) mask including all the muscle regions and excluding the bone and bone marrow regions in the tibia and fibula, (d) typical T₂-weighted FSE image and superimposed muscular ROIs used for the evaluation of fat distribution, (e) masks of 6 muscular ROIs, and (f) mask of soft tissue excluding subcutaneous fat and 6 muscular ROIs. Three muscles (medial gastrocnemius-MG, lateral gastrocnemius-LG, soleus-SOL) and three muscle compartments (anterior compartment-AC, lateral compartment-LC, deep posterior compartment-DP) were used to define muscular regions. Fat within the mask of (c) corresponds to IMAT, fat within the mask of (e) corresponds to intraMF, and the fat within the mask of (f) corresponds to interMF.

Figure 2

Comparison of water/fat separation results at a representative slice for a control subject A (age 63, BMI 26.8) and a diabetic subject B (age 63, BMI 28.3): water separated image, fat separated image and fat fraction map. Colorbar corresponds to fat fraction values in %. The arrow points to an area in the water separated image affected by coil sensitivity profile effects.

Figure 3

Comparison of fat distribution at a representative slice between a control subject A (age 63, BMI 26.8) and a diabetic subject B (age 63, BMI 28.3). The first column shows the compartmentalization of TAT between SAT, interMF and intraMF. The second column shows the compartmentalization of TAT between SAT and IMAT. The third column shows the compartmentalization of IMAT between interMF and intraMF. The employed color coding scheme was based on the assignment of blue for SAT, yellow for IMAT, red for interMF and green for intraMF regions. The color-coded maps were weighted by the fat fraction map values.

Figure 4

Statistical analysis results: (a) variation of distribution of IMAT between interMF and intraMF compartments and (c) variation of distribution of IMAT between the six segmented muscle regions in the control and diabetes groups under study. The symbol ** refers to statistical significance with p<0.05 for the difference between the two groups.