Accuracy, Reproducibility and Repeatability of Ultrasonography in the Assessment of Abdominal Adiposity

Rationale and Objectives

Despite improvements in the methods used in body composition analysis, some goals remain far from clinical practice. Among them, the most important is the quantification of intra-abdominal adipose tissue. Fat distribution is a key point in the assessment of cardiovascular and metabolic risk status. The aim of this study was to define the accuracy, reproducibility, and repeatability of ultrasonography in the evaluation of abdominal adiposity.

Materials and Methods

Twenty-six nonobese patients (group A) who underwent computed tomographic (CT) abdominal imaging and 29 obese patients (group B) were enrolled. Patients from both groups were independently evaluated using ultrasound by three radiologists; computed tomography–like conditions were reproduced, and six main parameters of subcutaneous and internal adiposity were measured (as well as three derived indexes) with both linear and convex probes. In group A, the same measurements were also obtained on CT images. Time spent for every ultrasound session was recorded. Results were analyzed using Lin’s concordance correlation (ρ), intraclass correlation, and linear regression analysis (and analysis of variance).

Results

Three patients were excluded from group A after CT scans because of technical problems. Mesenteric fat thickness did not show significant correlations and reliability. Strong correlations between ultrasound and CT measurements were observed for all other visceral and subcutaneous parameters (ρ = 0.85–0.96). Intraobserver and interobserver agreement was excellent in both groups (repeatability: ρ = 0.83–0.99 for group A, ρ = 0.90–0.99 for group B; reproducibility: intraclass correlation coefficient = 0.90–0.99 for groups A and B). The mean time spent was 95 ± 21 seconds for group A (mean body mass index, 27.4 ± 2.4 kg/m 2 ) and 129 ± 33 seconds for group B (mean body mass index, 37.3 ± 11.9 kg/m 2 ).

Conclusions

Ultrasound is accurate, reproducible, and fast in the analysis of abdominal adiposity. It offers a regional, easy, and close-at-hand evaluation of subcutaneous and visceral fat compartments. This should be taken into consideration when clinical routine examinations are performed or to evaluate patients with specific metabolic diseases before and after treatment.

The study of body composition (BC) continues to hold a prominent role in scientific research, although attention has shifted predominantly to clinical applications. BC analysis, quantification, and description of the distribution of adipose tissue are integral in the study of obesity and many other physiologic, paraphysiologic, and pathologic conditions . Moreover, adipose tissue is considered the biggest “gland” of the human body, and its endocrine functions are increasingly discovered and understood .

Obesity is described as a major public health problem by the World Health Organization, which uses the term globesity to reflect a global epidemic impact of the disease . In fact, the worldwide prevalence of overweight in children and young people is approximately 10% (2%–3% for obesity), while 23% and 10% of the world’s adult population is overweight and obese, respectively . If attention is focused on industrialized countries (established market economies), the prevalence of overweight rises to 41.0% and 28.6% for men and women, respectively, and the prevalence of obesity is 19.1% and 22.2% . Cameron et al as well as many contributions in the literature have presented and discussed the burden of metabolic syndrome and diabetes, both problems related to fat .

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Materials and methods

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Abdominal Adiposity Measures

Thickness measurements

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Adiposity indexes

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Statistical Analysis

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Results

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Correlation Between Ultrasound and CT Imaging

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Table 1

CT and Ultrasound Measures in Groups A and B

Measure Group A Group B CT Imaging (cm) Ultrasound (cm) Ultrasound (cm) Minimum subcutaneous fat thickness 1.29 ± 0.72 1.15 ± 0.67 1.83 ± 0.77 Maximum preperitoneal fat thickness 1.73 ± 0.57 1.77 ± 0.59 1.92 ± 0.55 Maximum subcutaneous fat thickness A 2.49 ± 1.16 2.50 ± 1.00 3.45 ± 1.31 Maximum subcutaneous fat thickness B 2.90 ± 1.42 2.83 ± 1.45 4.60 ± 1.75 Intra-abdominal fat thickness 7.31 ± 2.53 7.40 ± 1.71 8.21 ± 2.75 Mesenteric fat thickness 0.52 ± 0.14 0.42 ± 0.15 0.49 ± 0.20 WFI 0.78 ± 0.45 0.70 ± 0.48 1.05 ± 0.61 MAR-A 0.36 ± 0.15 0.39 ± 0.16 0.48 ± 0.26 MAR-B 0.41 ± 0.17 0.43 ± 0.23 0.61 ± 0.29

Data are expressed as mean ± standard deviation.

CT, computed tomographic; MAR-A, maximum abdominal ratio A (maximum subcutaneous fat thickness A/intra-abdominal fat); MAR-B, maximum abdominal ratio B (maximum subcutaneous fat thickness B/intra-abdominal fat); WFI, wall fat index (minimum subcutaneous fat/maximum preperitoneal fat).

Table 2

Ultrasound Compared to CT Measurements and Indexes of Abdominal Adipose Thicknesses ( n = 23)

CT Measures Ultrasound Measures Radiologist 1 Radiologist 2 Radiologist 3 Radiologist Mean ρ 95% CI ρ 95% CI ρ 95% CI ρ 95% CI Minimum subcutaneous fat thickness 0.94 § 0.84 to 0.98 0.96 § 0.85 to 0.99 0.92 ‡ 0.77 to 0.97 0.94 § 0.89 to 0.97 Maximum preperitoneal fat thickness 0.92 § 0.78 to 0.97 0.83 † 0.44 to 0.96 0.81 † 0.47 to 0.94 0.87 § 0.76 to 0.93 Maximum subcutaneous fat thickness A 0.96 § 0.90 to 0.99 0.92 ‡ 0.70 to 0.98 0.99 ‡ 0.97 to 1.00 0.96 § 0.93 to 0.98 Maximum subcutaneous fat thickness B 0.98 § 0.94 to 0.99 0.96 § 0.85 to 0.99 0.89 ‡ 0.72 to 0.96 0.95 § 0.90 to 0.97 Intra-abdominal fat thickness 0.84 § 0.61 to 0.94 0.75 ∗ 0.28 to 0.93 0.93 ‡ 0.76 to 0.98 0.85 § 0.73 to 0.92 Mesenteric fat thickness 0.14 −0.06 to 0.33 0.07 −0.48 to 0.58 0.21 −0.33 to 0.64 0.18 −0.06 to 0.41 WFI 0.90 § 0.75 to 0.96 0.95 § 0.80 to 0.99 0.85 § 0.61 to 0.94 0.90 § 0.82 to 0.95 MAR-A 0.92 § 0.81 to 0.97 0.81 † 0.40 to 0.95 0.92 § 0.73 to 0.98 0.89 § 0.80 to 0.94 MAR-B 0.91 § 0.78 to 0.96 0.92 ‡ 0.72 to 0.98 0.84 ‡ 0.60 to 0.94 0.89 § 0.80 to 0.94

Lin’s concordance correlations were used to compare ultrasound and CT measures.

CI, confidence interval; CT, computed tomographic; MAR-A, maximum abdominal ratio A (maximum subcutaneous fat thickness A/intra-abdominal fat); MAR-B, maximum abdominal ratio B (maximum subcutaneous fat thickness B/intra-abdominal fat); WFI, wall fat index (minimum subcutaneous fat/maximum preperitoneal fat).

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Reproducibility

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Table 3

Repeatability and Reproducibility of Sonographic Measurements and Indexes of Abdominal Adipose Thicknesses in Group A ( n = 23)

Measure Raters Repeatability Reproducibility Radiologist 1 Radiologist 1 vs Radiologist 2 Radiologist 1 vs Radiologist 3 Radiologist 2 vs Radiologist 3 Total ρ 95% CI ρ 95% CI ρ 95% CI ρ 95% CI ICC 95% CI Minimum subcutaneous fat thickness 0.95 § 0.85 to 0.98 0.97 § 0.89 to 0.99 0.94 § 0.83 to 0.98 0.95 § 0.81 to 0.99 0.99 0.96 to 1.00 Maximum preperitoneal fat thickness 0.91 § 0.74 to 0.97 0.77 † 0.33 to 0.93 0.75 ∗ 0.38 to 0.91 0.76 ∗ 0.19 to 0.94 0.90 0.66 to 0.98 Maximum subcutaneous fat thickness A 0.94 § 0.85 to 0.98 0.92 § 0.78 to 0.97 0.95 § 0.86 to 0.98 0.93 § 0.74 to 0.98 0.98 0.93 to 0.99 Maximum subcutaneous fat thickness B 0.99 § 0.96 to 1.00 0.99 § 0.95 to 1.00 0.90 § 0.69 to 0.97 0.98 § 0.91 to 1.00 0.99 0.98 to 1.00 Intra-abdominal fat thickness 0.97 § 0.90 to 0.99 0.97 § 0.90 to 0.99 0.91 § 0.71 to 0.97 0.87 † 0.51 to 0.97 0.97 0.88 to 0.99 Mesenteric fat thickness 0.30 −0.21 to 0.67 0.17 −0.31 to 0.58 0.26 −0.11 to 0.57 0.47 −0.24 to 0.86 0.51 −0.28 to 0.88 WFI 0.90 § 0.73 to 0.97 0.95 § 0.85 to 0.99 0.84 ‡ 0.56 to 0.95 0.87 ‡ 0.66 to 0.96 0.97 0.92 to 0.99 MAR-A 0.83 ‡ 0.59 to 0.93 0.90 ‡ 0.69 to 0.97 0.92 § 0.78 to 0.98 0.82 † 0.40 to 0.96 0.96 0.88 to 0.99 MAR-B 0.97 § 0.91 to 0.99 0.98 § 0.93 to 0.99 0.85 ‡ 0.55 to 0.95 0.95 § 0.88 to 0.98 0.99 0.96 to 1.00

Lin’s concordance correlations were used to evaluate repeatability and reproducibility between two radiologists, while intraclass correlation was used to evaluate reproducibility for all three radiologists.

CI, confidence interval; ICC, intraclass correlation coefficient; MAR-A, maximum abdominal ratio A (maximum subcutaneous fat thickness A/intra-abdominal fat); MAR-B, maximum abdominal ratio B (maximum subcutaneous fat thickness B/intra-abdominal fat); WFI, wall fat index (minimum subcutaneous fat/maximum preperitoneal fat).

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Table 4

Repeatability and Reproducibility of Ultrasound Measurements and Indexes of Abdominal Adipose Thicknesses in Group B ( n = 29)

Measure Raters Repeatability Reproducibility Radiologist 1 Radiologist 1 vs Radiologist 2 Radiologist 1 vs Radiologist 3 Radiologist 2 vs Radiologist 3 Total ρ 95% CI ρ 95% CI ρ 95% CI ρ 95% CI ICC 95% CI Minimum subcutaneous fat thickness 0.93 ‡ 0.83 to 0.97 0.78 ∗ 0.45 to 0.93 0.76 ∗ 0.40 to 0.92 0.86 ‡ 0.71 to 0.94 0.92 0.81 to 0.97 Maximum preperitoneal fat thickness 0.92 ‡ 0.82 to 0.97 0.77 ∗ 0.42 to 0.92 0.91 ‡ 0.73 to 0.97 0.80 ‡ 0.56 to 0.91 0.94 0.84 to 0.98 Maximum subcutaneous fat thickness A 0.95 ‡ 0.89 to 0.98 0.96 ‡ 0.87 to 0.98 0.97 ‡ 0.93 to 0.99 0.95 ‡ 0.88 to 0.98 0.99 0.97 to 1.00 Maximum subcutaneous fat thickness B 0.99 ‡ 0.97 to 1.00 0.98 ‡ 0.95 to 0.99 0.98 ‡ 0.95 to 0.99 0.98 ‡ 0.95 to 0.99 0.99 0.98 to 1.00 Intra-abdominal fat thickness 0.98 ‡ 0.94 to 0.99 0.91 ‡ 0.76 to 0.97 0.93 ‡ 0.80 to 0.98 0.93 ‡ 0.84 to 0.97 0.97 0.93 to 0.99 Mesenteric fat thickness 0.51 ∗ 0.18 to 0.74 0.21 −0.27 to 0.60 0.12 −0.39 to 0.58 0.42 ∗ 0.15 to 0.66 0.53 −0.11 to 0.84 WFI 0.90 ‡ 0.76 to 0.95 0.72 ∗ 0.31 to 0.90 0.80 † 0.51 to 0.93 0.75 † 0.50 to 0.88 0.90 0.75 to 0.97 MAR-A 0.98 ‡ 0.95 to 0.99 0.96 ‡ 0.88 to 0.99 0.95 ‡ 0.86 to 0.98 0.93 ‡ 0.85 to 0.97 0.98 0.95 to 0.99 MAR-B 0.95 ‡ 0.91 to 0.97 0.87 ‡ 0.66 to 0.96 0.87 ‡ 0.75 to 0.93 0.77 ‡ 0.59 to 0.88 0.93 0.83 to 0.98

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Repeatability

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Discussion

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Conclusions

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Accuracy, Reproducibility and Repeatability of Ultrasonography in the Assessment of Abdominal Adiposity

Rationale and Objectives

Materials and Methods

Results

Conclusions

Materials and methods

Abdominal Adiposity Measures

Thickness measurements

Adiposity indexes

Statistical Analysis

Results

Correlation Between Ultrasound and CT Imaging

Reproducibility

Repeatability

Discussion

Conclusions

References

Further Reading

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