Quantitative 99mTc-MDP SPECT/CT as an alternative to 18F-NaF PET/CT for objective assessment of osteoblastic bone metastases

Objective: To investigate the correlation between the standardized uptake value (SUV) metrics derived from technetium-99m (Tc-99m) methylene diphosphonate (MDP) single photon emission computed tomography/computed tomography (SPECT/CT) and fluorine-18 (F-18) sodium fluoride (NaF) positron emission tomography (PET)/CT. Subjects and Methods: A total of 129 metastatic lesions from 14 patients who underwent both Tc-99m-MDP SPECT/CT and F-18-NaF PET/CT within one month were included in the analyses. The lesions with markedly increased uptake were semi-automatically segmented into a volume of interest in both SPECT and PET images by taking the 42% of maximum uptake as a threshold. Maximum, average and minimum SUV (namely, SUVmax, SUVmean and SUVmin) were recorded for each lesion. The strength of correlation was evaluated with Pearson's correlation analysis. Results:The correlation coefficitients for SUVmax, SUVmean and SUVmin derived from SPECT and PET images were 0.652, 0.653 and 0.635, respectively (all P<0.001). Lesions with a volume of at least 5cm(3) demonstrated a stronger correlation, increasing the correlation coefficients to 0.714, 0.724 and 0.686, respectively (all P<0.001). The strongest correlation was seen in the lesions of the appendicular skeleton, with coefficients for SUVmax, SUVmean and SUVmin being 0.769, 0.791 and 0.761, respectively (all P<0.001). Conclusions:The SUV metrics derived from 99 Tc-99m-MDP SPECT/CT strongly correlate with F-18-NaF PET, especially for relatively large lesions located in the appendicular skeleton. Technetium-99m-MDP SPECT/CT could potentially be used as an alternative method to F-18-NaF PET/CT for quantitative evaluation and objective follow-up of bone metastases.