Volumetric Ultrasound of the Plantar Soft Tissue Under Bodyweight Loading

Objective: This work aims to develop a device capable of acquiring volumetric scans of the plantar soft tissue in naturally loaded and unloaded states using ultrasound B-mode imaging and shear wave elastography. Methods: Materials were investigated for acoustic transmission and bodyweight loading. A mechanical scanning apparatus was constructed using a compatible load bearing material and two perpendicular linear actuators. Custom software was developed to control the scanner, record subject and scan information, and reconstruct acquired ultrasound images and shear wave speed values into a volume. The system was evaluated using custom-developed ultrasound phantoms. Results: Plastic materials reduced axial and lateral resolution by 0.25 - 0.5 mm and reduced SWE values by 0.8 to 26 kPa. The developed system produced volumetric scans within 0.1 to 1.6 mm of expected dimensions on a geometric phantom compared to 0 to 0.6 mm in standard computed tomography. Acoustic thermal increases were 0 °C for B-mode and 0.9 to 2.9 °C for SWE. Volumes of an anatomically realistic phantom and a pilot scan yielded clear anatomic features. Conclusion: The resulting system is capable of producing volumetric plantar soft tissue scans in both B-mode and shear wave elastography with resolution on par with existing volumetric medical imaging systems. Significance: This system images plantar soft tissue volumes under physiologic loads.