Tc-99m-DPD xSPECT Bone Scan Quantification Of Subchondral Bone Uptake: An Analysis Of The Osteoarthritic Sacroiliac Joint

Introduction: Bone scintigraphy with Tc-99m-labeled DPD is able to identify osteoblastic reactions in the spectrum of osteoarthritic bone changes with high sensitivity, especially in the sacroiliac joint (SIJ). The aim of this study was to investigate the role of Tc-99m DPD absolute uptake quantification with xSPECT/CT in normal and osteoarthritic sacroiliac subchondral bone and to correlate obtained SUV to CT density using Hounsfield units (HU).

Methods: A total number of 34 SIJ in 17 patients (mean age 68±11 years) were retrospectively assessed.

Quantitative xSPECT/CT (Symbia Intevo, Siemens Healthineers, Erlangen, Germany) was acquired and SUV quantified on post-processed images using SUVmax, SUVmean (g/mL) in sacral and iliac subchondral bone in the superior, anterior and inferior regions of the SIJ. HU of the same regions of interest were measured on CT. SUVmax, SUV mean and CT density was compared between no/minimal and advanced OA groups. We used receiver operating characteristics (ROC) curves to determine the optimum SUVmax cutoff value to distinguish between no/minimal and advanced OA groups.

Results: Fifteen SIJ were classified as no/minimal OA and 19 as advanced OA based on CT analysis.

Mean values of SUVmax and CT density (HU) of the three analysed SIJ compartments were significantly higher in the advanced versus no/minimal OA group within both the sacral (8.5±1.5 versus 5.8±1.2, p<0.001 and 389±80 versus 280±53, p<0.001, respectively) and the iliac sides (10.3±1.2 versus 7.5±1, p<0.001 and 538±134 versus 426±133, p=0.021, respectively). Using a SUVmax cutoff of 8 g/mL for the detection of advanced OA in the subchondral bone, sensitivity, specificity and AUC were 100%, 93%, 0.968, respectively.

We found a positive correlation between SUVmax and CT density (HU) only in the iliac subchondral bone in the group with no/minimal OA (rho=0.596, p=0.019).

Conclusions: This study showed significant differences in Tc-99m-DPD uptake on bone scan between OA and no/minimal OA in the subchondral bone of all three superior, anterior and inferior compartments of both sacral and iliac sides of the sacroiliac joint based on quantitative data analysis. There were significantly higher SUVmax and CT density in the advanced OA group. Thus, integrating quantitative analysis of bone scan for the SIJ might be valuable in increasing sensitivity for the initial detection and potentially for stratification and evolution assessment of degenerative changes.