High-frequency spectral ultrasound imaging (SUSI) visualizes early post-traumatic heterotopic ossification (HO) in a mouse model

Purpose: Early treatment of heterotopic ossification (HO) is currently limited by delayed diagnosis due to limited visualization at early time points. In this study, we validate the use of spectral ultrasound imaging (SUSI) in an animal model to detect HO as early as one week after burn tenotomy. Methods: Concurrent SUSI, micro CT, and histology at 1, 2, 4, and 9 weeks post-injury were used to follow the progression of HO after an Achilles tenotomy and 30% total body surface area burn (n = 3–5 limbs per time point). To compare the use of SUSI in different types of injury models, mice (n = 5 per group) underwent either burn/tenotomy or skin incision injury and were imaged using a 55 MHz probe on VisualSonics VEVO 770 system at one week post injury to evaluate the ability of SUSI to distinguish between edema and HO. Average acoustic concentration (AAC) and average scatterer diameter (ASD) were calculated for each ultrasound image frame. Micro CT was used to calculate the total volume of HO. Histology was used to confirm bone formation. Results: Using SUSI, HO was visualized as early as 1 week after injury. HO was visualized earliest by 4 weeks after injury by micro CT. The average acoustic concentration of HO was 33% more than that of the control limb (n = 5). Spectroscopic foci of HO present at 1 week that persisted throughout all time points correlated with the HO present at 9 weeks on micro CT imaging. Conclusion: SUSI visualizes HO as early as one week after injury in an animal model. SUSI represents a new imaging modality with promise for early diagnosis of HO.