Stress fracture is a common condition in athletes and military personnel yet objective methods for detection and tracking of stress fractures (e.g., MR and scintigraphy) remain complex and expensive. Methods involving ultrasound are in common use; however, they are thus far subjective (relying on patient report of pain). The goal of this work is to develop quantitative and sensitive ultrasonic evaluation methods that could be deployed broadly in smaller clinical setting for use by a wide range of medical professionals. Such methods would complement beam-formed images of the bone surface by adding information about even sub-wavelength features. We have demonstrated that small imperfections on the bone surface significantly alter the characteristics of the reflectivity as made evident in the relative magnitude of the specular vs. diffuse scatter. In this paper we will present our work toward developing methods for acquiring, enhancing, visualizing, and evaluating such effects. We will present results from measurements with ex vivo bone samples and phantoms, and discuss the ultimate applicability of our methods to in vivo diagnosis.
Sound speed inversions made using simulated time of flight data from a numerical limb-mimicking phantom comprised of soft tissue and a bone inclusion demonstrate that wave front tracking forward modeling combined with L1 regularization may lead to accurate estimates of bone sound speed. Ultrasonic tomographic imaging of limbs has the potential to impact prosthetic socket fitting, as well as detect and track muscular dystrophy diseases, osteoporosis and bone fractures at low cost and without radiation exposure. Research in ultrasound tomography of bones has increased in the last 10 years, however, methods delivering clinically useful sound speed inversions are lacking.
Conventional processes for prosthetic socket fabrication are heavily subjective, often resulting in an interface to the human body that is neither comfortable nor completely functional. With nearly 100% of amputees reporting that they experience discomfort with the wearing of their prosthetic limb, designing an effective interface to the body can significantly affect quality of life and future health outcomes. Active research in medical imaging and biomechanical tissue modeling of residual limbs has led to significant advances in computer aided prosthetic socket design, demonstrating an interest in moving toward more quantifiable processes that are still patient-specific. In our work, medical ultrasonography is being pursued to acquire data that may quantify and improve the design process and fabrication of prosthetic sockets while greatly reducing cost compared to an MRI-based framework. This paper presents a prototype limb imaging system that uses a medical ultrasound probe, mounted to a mechanical positioning system and submerged in a water bath. The limb imaging is combined with three-dimensional optical imaging for motion compensation. Images are collected circumferentially around the limb and combined into cross-sectional axial image slices, resulting in a compound image that shows tissue distributions and anatomical boundaries similar to magnetic resonance imaging. In this paper we provide a progress update on our system development, along with preliminary results as we move toward full volumetric imaging of residual limbs for prosthetic socket design. This demonstrates a novel multi-modal approach to residual limb imaging.