Validation of Peripheral Quantitative Computed Tomography-Derived Thigh Adipose Tissue Subcompartments in Young Girls Using a 3 T MRI Scanner

Abstract

The ability to assess skeletal muscle adipose tissue is important given the negative clinical implications associated with greater fat infiltration of the muscle. Computed tomography and magnetic resonance imaging (MRI) are highly accurate for measuring appendicular soft tissue and muscle composition, but have limitations. Peripheral quantitative computed tomography (pQCT) is an alternative that investigators find valuable because of its low radiation, fast scan time, and comparatively lower costs. The present investigation sought to assess the accuracy of pQCT-derived estimates of total, subcutaneous, skeletal muscle, intermuscular, and calculated intramuscular adipose tissue areas, and muscle density in the midthigh of young girls using the gold standard, 3 T MRI, as the criterion. Cross-sectional data were analyzed for 26 healthy girls aged 9-12 years. Midthigh soft tissue composition was assessed by both pQCT and 3 T MRI. Mean tissue area for corresponding adipose compartments by pQCT and MRI was compared using t tests, regression analysis, and Bland-Altman plots. Muscle density was regressed on MRI skeletal muscle adipose tissue, intermuscular adipose tissue, and intramuscular adipose tissue, each expressed as a percentage of total muscle area. Correlations were high between MRI and pQCT for total adipose tissue (r² = 0.98), subcutaneous adipose tissue (r² = 0.95), skeletal muscle adipose tissue (r² = 0.83), and intermuscular adipose tissue (r² = 0.82), and pQCT muscle density correlated well with both MRI skeletal muscle adipose tissue (r² = 0.70) and MRI intermuscular adipose tissue (r² = 0.70). There was a slight, but statistically significant underestimation by pQCT for total and subcutaneous adipose tissue, whereas no significant difference was observed for skeletal muscle adipose tissue. Both pQCT-estimated intramuscular adipose tissue and muscle density were weakly correlated with MRI-intramuscular adipose tissue. We conclude that pQCT is a valid measurement technique for estimating all adipose subcompartments, except for intramuscular adipose tissue, for the midthigh region in young/adolescent girls.

Keywords: Adipose; intermuscular; intramuscular; muscle density; pQCT.

Figure 1

(A) Total adipose tissue pQCT vs MRI, solid line indicates line of identity; (B) Bland Altman plot of MRI-pQCT total adipose tissue difference against average of MRI and pQCT; (C) Plot of MRI-pQCT total adipose tissue difference against thigh circumference; (D) Plot of MRI-pQCT total adipose tissue difference against BMI. B-D: Solid line indicates mean difference and large dashed lines indicate ±2 SD.

Figure 2

(A) Subcutaneous adipose tissue pQCT vs MRI, solid line indicates line of identity; (B) Bland Altman plot of MRI-pQCT subcutaneous adipose tissue difference against average of MRI and pQCT; (C) Plot of MRI-pQCT subcutaneous adipose tissue difference against thigh circumference; (D) Plot of MRI-pQCT subcutaneous adipose tissue difference against BMI. B-D: Solid line indicates mean difference and large dashed lines indicate ±2 SD.

Figure 3

(A) Skeletal muscle adipose tissue pQCT vs MRI, solid line indicates line of identity; (B) Bland Altman plot of MRI-pQCT skeletal muscle adipose tissue difference against average of MRI and pQCT; (C) Plot of MRI-pQCT skeletal muscle adipose tissue difference against thigh circumference; (D) Plot of MRI-pQCT skeletal muscle adipose tissue difference against BMI. B-D: Solid line indicates mean difference and large dashed lines indicate ±2 SD.

Figure 4

(A) Intermuscular adipose tissue pQCT vs MRI, solid line indicates line of identity; (B) Bland Altman plot of MRI-pQCT intermuscular adipose tissue difference against average of MRI and pQCT; (C) Plot of MRI-pQCT intermuscular adipose tissue difference against thigh circumference; (D) Plot of MRI-pQCT intermuscular adipose tissue difference against BMI. B-D: Solid line indicates mean difference and large dashed lines indicate ±2 SD.

Figure 5

(A) Intramuscular adipose tissue pQCT vs MRI, solid line indicates line of identity; (B) Bland Altman plot of MRI-pQCT intramuscular adipose tissue difference against average of MRI and pQCT; (C) Plot of MRI-pQCT intramuscular adipose tissue difference against thigh circumference; (D) Plot of MRI-pQCT intramuscular adipose tissue difference against BMI. B-D: Solid line indicates mean difference and large dashed lines indicate ±2 SD.

Figure 6

Plots of pQCT-derived thigh muscle density against (A) thigh skeletal muscle adipose tissue area from MRI, (B) thigh intermuscular adipose tissue area from MRI, and (C) thigh intramuscular adipose tissue area from MRI. Solid line indicates line of identity.