Computerized Method for Automatic Evaluation of Lean Body Mass from PET/CT: Comparison with Predictive Equations

CT has become an established method for calculating body composition, but it requires data from the whole body, which are not typically obtained in routine PET/CT examinations. A computerized scheme that evaluates whole-body lean body mass (LBM) based on CT data from limited-whole-body coverage was developed. The LBM so obtained was compared with results from conventional predictive equations. Methods: LBM can be obtained automatically from limited-whole-body CT data by 3 means: quantification of body composition from CT images in the limited-whole-body scan, based on thresh-olding of CT attenuation; determination of the range of coverage based on a characteristic trend of changing composition across different levels and pattern recognition of specific features at strategic positions; and estimation of the LBM of the whole body on the basis of a predetermined relationship between pro-portion of fat mass and extent of coverage. This scheme was validated using 18 whole-body PET/CT examinations truncated at different lengths to emulate limited-whole-body data. LBM was also calculated using predictive equations that had been reported for use in SUV normalization. Results: LBM derived from limited-whole-body data using the proposed method cor-related strongly with LBM derived from whole-body CT data, with correlation coefficients ranging from 0.991 (shorter cover-age) to 0.998 (longer coverage) and SEMs of LBM ranging from 0.14 to 0.33 kg. These were more accurate than results from different predictive equations, which ranged in correlation co-efficient from 0.635 to 0.970 and in SEM from 0.64 to 2.40 kg. Conclusion: LBM of the whole body could be automatically estimated from CT data of limited-whole-body coverage typi-cally acquired in PET/CT examinations. This estimation allows more accurate and consistent quantification of metabolic activ-ity of tumors based on LBM-normalized standardized uptake value. Key Words: lean body mass; standardized uptake valu