Rationale and Objectives
The aim of this study was to determine the accuracy and reproducibility of low-dose computed tomography (CT) and magnetic resonance (MR) for abdominal adipose tissue quantification on phantom and human studies.
Materials and Methods
An adiposity phantom (with known internal/external oil volumes) was scanned at three different tube voltages (140, 120, and 90 kVp) using a 16-detector row CT scanner and was imaged using a T1-weighted spin echo MR sequence. For human studies, whole-volume coverage of the abdomen was obtained using CT (at 140 and 90 kVp) and T1-weighted spin echo MR imaging from five obese male volunteers (mean age, 40.6 years; mean body mass index, 30.2). The volumes of total, visceral, and subcutaneous adipose tissues (TAT, VAT, and SAT, respectively) were calculated independently by two radiologists for each CT scan and MR imaging using a computer-aided semiautomatic program.
Results
The estimated radiation dose could be reduced by approximately 75% with a 90-kVp protocol as compared with the 140-kVp protocol. Phantom studies showed that there was no statistically significant difference between the four methods in estimating the percentage predicted of the true volumes (measurement errors <4% for all methods, P > .05). In human studies, we found no statistically significant difference between the three methods in TAT, VAT, and SAT volumes ( P > .05). Inter- and intraobserver reproducibilities of the CT volume estimates using the 90-kVp protocol were better than those obtained from MR imaging (κ > 0.9 versus 0.4–0.5; coefficient of variation < 1% versus 15–22%).
Conclusion
Low-dose CT provides accurate and reproducible measurement of abdominal adipose tissue volumes with a relevant dose reduction.
There is growing evidence that obesity is related to several metabolic disturbances, such as diabetes, hypertension, and cardiovascular disease. In recent years, it has been suggested that the metabolic risks associated with obesity are more closely correlated with adipose tissue within the viscera (visceral adipose tissue, VAT) than subcutaneous adipose tissue (SAT) surrounding the abdomen ( ).
Therefore accurate and reproducible quantification of total and regional abdominal fat is of great importance for clinical and research purposes. Many indirect and direct methods have been used for the measurement of abdominal fat distribution, including anthropometry, bioelectrical impedance, and dual-energy x-ray absorptiometry ( ). It is generally accepted that computed tomography (CT) and magnetic resonance (MR) imaging are the best in vivo methods for directly assessing regional adipose tissue content in human subjects. CT is an excellent technique to measure cross-sectional areas of adipose tissue, but the exposure to ionizing radiation limits broad and repeated application in healthy subjects. Although MR offers specific advantages for measuring abdominal fat (such as that it does not require radiation exposure), its usage may be limited by accessibility and cost.
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Materials and methods
Phantom Study
Phantom
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CT
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MR
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Volunteer Study
Volunteers
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CT
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MR
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Radiation Dose Measurement
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Fat Volume Measurements
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CT
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Table 1
Summary of CT Numbers of Vegetable Oil in Phantom and Adipose Tissue in Volunteers Obtained at 140, 120, and 90 kVp
Mean Attenuation Standard Deviation Minimum Value Maximum Value Vegetable oil in phantom 140 kVp −109.3 5.1 −133 −91 120 kVp −113.8 6.6 −148 −85 90 kVp −128.9 11.4 −164 −77 Fat tissue in volunteer 140 kVp −106.7 8.5 −143 −71 90 kVp −117.1 16.2 −169 −55
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MR
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Statistical Analysis
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Results
Radiation Exposure in CT Scans
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Table 2
Summary of Radiation Dose Measurements at 140, 120, and 90 kVp
140 kVp 120 kVp 90 kVp Phantom CT dose index volume (mGy) 18.7 ± 0.2 12.0 ± 0.2 5.1 ± 0.1 Dose reduction (%) ⁎ 39.1 ± 0.4 73.4 ± 0.7 Volunteers (n = 5) CT dose index volume (mGy) 18.8 ± 0.2 5.0 ± 0.1 Dose length product (mGy cm) 953.2 ± 21.3 253.8 ± 38.7 Effective dose (mSv) 14.3 ± 1.8 3.8 ± 0.6 Dose reduction (%) ⁎ 73.5 ± 0.8
Note.—Data are mean ± standard deviation.
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Phantom Study
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Table 3
Measured Volumes of Adipose Tissues using CT and MR in Phantom
CT protocol MR 140 kVp 120 kVp 90 kVp TAT 98.7 98.6 99.1 101.1 VAT 97.4 97.5 98.9 98.7 SAT 100.2 99.9 99.3 103.9 VAT/SAT 97.2 97.6 99.6 95.0
Data are mean estimate of true volumes (%). All data are not statistically significant.
TAT = total adipose tissue; VAT = visceral adipose tissue; SAT = subcutaneous adipose tissue.
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Volunteer Study
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Table 4
Measured Volumes of Adipose Tissues using CT and MR in 5 Volunteers
CT Protocol MR 140 kVp 90 kVp TAT (mL) 13,923 ± 1,965 13,938 ± 1,921 14,483 ± 2,292 VAT (mL) 5,665 ± 469 5,781 ± 430 5,859 ± 498 SAT (mL) 8,074 ± 1,282 8,177 ± 1,310 8,657 ± 1,420 VAT/SAT 0.73 ± 0.13 0.71 ± 0.14 0.68 ± 0.19
Data are mean ± standard deviation. All data are not statistically significant.
TAT = total adipose tissue; VAT = visceral adipose tissue; SAT = subcutaneous adipose tissue.
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Discussion
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