Optimum lean body formulation for correction of standardized uptake value in PET imaging

Standardized uptake value (SUV) normalized by lean body mass ([LBM] SUL) is becoming a popular metric for quantitative assessment of clinical PET. Sex-specific quantitative effects of different LBM formulations on liver SUV have not been well studied. Methods: ¹⁸FFDG PET/CT scans from 1,033 consecutive adult (501 women, 532 men) studies were reviewed. Liver SUV was measured with a 3-cmdiameter spheric region of interest in the right hepatic lobe and corrected for LBM using the sex-specific James and Janmahasatian formulations. Results: Body weight was 71.0 ± 20.7 kg (range, 18.0-175.0 kg) and 82.9 ± 18.6 kg (range, 23.0-159.0 kg) for women and men, respectively. SUV, based on body weight, has a significantly positive correlation with weight for both women (r 5 0.58, P < 0.0001) and men (r 5 0.54, P < 0.0001). This correlation is reduced in men (r 5 0.11, P 5 0.01) and becomes negative for women (r 5 -0.35, P 5 0.0001) with the James formulation of SUL. This negative correlation was eliminated when the very obese women (body mass index ≥ 35) were excluded from the analysis (r 5 0.13, P 5 0.8). The Janmahasatian formulation annuls the correlation between SUL and weight for women (r 5 0.04, P 5 0.4) and decreases it for men (r 5 0.13, P 5 0.003). Conclusion: Hepatic correction with the more common James formulation for body lean mass breaks down and shows low SUL values in very obese patients. The adoption of the Janmahasatian formula for estimation of LBM in modern PET scanners and display workstations is recommended, in view of the increasing frequency of obesity.