Bone Health Assessment using Synthetic Aperture Ultrasound Reflectometry

Bone stress injuries (BSI) are caused by repetitive loading patterns that do not allow adequate time for bone remodeling. These injuries are most prevalent among endurance athletes and military personnel, particularly military recruits. Treatment for BSI usually includes some level of activity modification and, with prescribed recovery times of weeks to months, these injuries impose significant time lost from training or duties. The gold standard method for diagnosing and grading stress injuries is MRI. Ultrasound would be an attractive alternative or supplement for BSI diagnosis and recovery monitoring, since it can be applied at point-of-care locations and repeat scans are safe and relatively low cost. We describe the Image Registered Quantitative Ultrasound (IR-QUS) technique, aimed at evaluating BSI on the basis of surface roughness as an indicator of rapid bone remodeling. IR-QUS collects angle-diverse acoustic measurements on a focal point and detects relative increases in diffusive versus specular scattering. We demonstrate the sensitivity of this method to characterize surface roughness on the scale of tens of microns, and show the feasibility of detecting a localized field of fractures on an ex vivo intact bone sample. Experimental results suggest reliable detection of roughened surfaces with a diffuse-to-specular energy metric that increases by 10 dB relative to smooth regions.