The diagnostic value of quantitative 99m Tc-MDP SPECT/CT fusion imaging in the differential diagnosis of spinal infections

Aims To investigate the value of quantitative 99m Tc-labelled methylene diphosphonate ( 99m Tc-MDP) single-photon emission CT (SPECT)/CT fusion imaging in the differential diagnosis of spinal infections. Methods A total of 90 patients with confirmed spinal infections, prior to any clinical treatment, underwent 99m Tc-MDP SPECT/CT fusion imaging. The maximum, mean, and minimum standardized uptake values (SUVmax, SUVmean, SUVmin), bone metabolic volume (MBV), total bone uptake (TBU), and CT Hounsfield unit (HU) values were measured in both affected and normal vertebrae. Multidimensional comparisons of SPECT/CT parameters were performed, including within-subject analyses comparing affected and adjacent normal vertebrae in the same infection type, as well as inter-group comparisons across different types of spinal infections. Diagnostic performance was assessed using receiver operating characteristic (ROC) curve analysis to determine the area under the curve (AUC) and optimal cut-off values, while the linear associations between quantitative SPECT/CT parameters of affected vertebrae and laboratory biomarkers were evaluated. Results The median SUVmax of affected vertebrae in pyogenic spondylitis (PS) was 21.17 (IQR 17.19 to 22.01), significantly higher than that observed in spinal tuberculosis (STB) (17.57 (IQR 15.02 to 18.98)) and brucellar spondylitis (BS) (15.63 (IQR 14.28 to 16.90)). SUVmax demonstrated strong diagnostic performance in differentiating PS from BS, with an AUC of 0.852, yielding 95.0% sensitivity and 71.7% specificity at an optimal cut-off value of 18.51. Similarly, CT HU values showed moderate discriminative ability for distinguishing BS from STB, achieving an AUC of 0.741, with 80.0% sensitivity and 65.0% specificity at a cut-off of 706 HU. Furthermore, a strong positive correlation was observed between SUVmax and CT HU values across all three infection groups. In addition, SUVmax exhibited a significant positive correlation with serum inflammatory markers in patients with PS. Conclusion Quantitative 99m Tc-MDP SPECT/CT fusion imaging enables objective assessment of spinal infection severity, thereby facilitating the differential diagnosis of distinct aetiological types of spondylitis. Cite this article: Bone Joint Res 2026;15(11):1292–1306.