SPECT/CT imaging: quantifying 99mTc-MDP concentration in the spine and pelvis

Objective This study aimed to identify a relatively robust SUV for guiding clinical practice through quantitative measurement and comparison of various normalization methods based on the SUV of Tc-99m-MDP in the normal spine and pelvis using an integrated SPECT/CT scanner. Methods Between June 2017 and September 2019, a total of 500 oncology patients (mean age, 60.9; men, 66.0%) who underwent bone SPECT/CT scans with Tc-99m-MDP were enrolled in this retrospective study. The mean SUV (SUVmean) of 4962 spinal and pelvic bones was calculated based on the patients' body weight (BW), lean body mass (LBM), bone mineral content (BMC), body surface area (BSA), and body mass index (BMI), defined as SUVbw, SUVlbm, SUVbmc, SUVbsa, and SUVbmi, respectively. The coefficients of variation (CoVs) of the aforementioned parameters were compared, and the correlation and multiple linear regression analyses were used to compare the extent to which these parameters were affected by sex, age, height, weight, BMI, and CT values. Results The average SUVs in the normal spine and pelvis displayed a relatively wide variability: 4.573 +/- 1.972 for SUVbw, 3.555 +/- 1.517 for SUVlbm, 0.163 +/- 0.071 for SUVbmc, 0.124 +/- 0.052 for SUVbsa, and 1.668 +/- 0.732 for SUVbmi. In general, SUVbsa had relatively lowest CoV (42.1%) in all vertebrae and pelvis compared with other SUVs. For correlation analyses, all SUVs displayed weak but significant correlations with age and CT values. For regression analyses, SUVbsa was influenced only by age, BMI, and CT values independently. The effects of these variables on SUVbsa were all smaller than those on conventional SUVbw. Conclusions The SUVs of Tc-99m-MDP in normal bone derived from quantitative bone SPECT/CT could serve as a reference for evaluating tumor bone metastasis, but it should be assessed on a site-specific basis. SUVbsa exhibited superior robustness among all the SUV normalization variations, indicating potential clinical applications.