Evaluation of heterotopic ossification maturity using SPECT/CT and PET/CT in preclinical model

Heterotopic ossification (HO) is the formation of bone within soft tissue where bone normally does not exist. In general, it is characterized by highly active tissue with high bone turnover and rapid bone formation. It is of an utmost importance to precisely identify and accurately diagnose the maturity of HO as early surgical intervention may result in its recurrence. The objective of this work is the experimental evaluation of HO maturity stage using advanced noninvasive nuclear medicine techniques. The use of PET radiopharmaceuticals may result in a more specific diagnosis between the phases due to their higher sensitivity and better resolution compared to bone scan.

8-week-old Balb/c male mice underwent dual injury procedure, tenotomy and concurrent burn injury on the left side, to induce HO. The progression of HO was monitored by SPECT/CT and PET/CT weekly imaging with ^99mTc-MDP, [¹⁸F]NaF and [¹⁸F]FDG for up to 16 weeks.

There was a statistically significant increase of [¹⁸F]FDG uptake from week 1 to 2 and from week 2 to 6 with p values of 0.01 and 0.005; respectively, while there was a statistically significant decrease from week 7 to 14 with a p value of 0.008. There was a statistically significant increase of [¹⁸F]NaF uptake from week 2 to 5 and statistically significant decrease between weeks 7 and 14 with p values of 0.016 and 0.003; respectively. As for ^99mTc-MDP, the increase in the uptake from week 1 to 2 and from week 2 to 5 were not statistically significant with p values of 0.15 and 0.19; respectively. The decrease of uptake between week 7 and 14 was not statistically significant with a p value of 0.08.

Based on these findings, the use of noninvasive nuclear imaging modalities may assist in distinguishing between the immature and mature phases. The uptake of mainly [¹⁸F]FDG may indicate the early inflammatory phase, while the uptake of both [¹⁸F]FGD and [¹⁸F]NaF may suggest the immature phase, and an uptake of mainly [¹⁸F]NaF may indicate the maturity phase of HO.