Ultrasonic Tracker for Non-Invasive Musculoskeletal Tracking

Abstract

Monitoring bone location during orthopaedic surgery can be vital for precise surgical interventions and improved patient outcomes. However, achieving accurate and precise bone tracking non-invasively remains a challenge. This study introduces a novel method employing an optically tracked ultrasonic device attached to the skin, and utilising coherence of ultrasound backscatter for tracking. The research suggested that tracking the bone directly using coherence of bone backscatter was infeasible. However, by assessing the coherence of muscle and soft tissue backscatter, the relative motion of tissue could be estimated. Through a tailored compliance model, describing the relative motion between tissue and bone, the underlying bone motion could be discerned
via tracking tissue. Hence, the technique utilises both absolute positioning of the ultrasonic tracker through optical tracking, and relative positioning of tissue and bone.

In this study, the primary aim was to explore the feasibility of measuring relative tissue motion using coherence of ultrasound measurements. The approach taken involved simulating ultrasound scans of a 2-D cross-sectional human thigh model. The accuracy of tracking relative tissue motion was quantified in terms of Root Mean Square Error (RMSE). Sensor fusion, Bayesian estimation and training/testing techniques were employed for a comprehensive assessment of accuracy. To validate simulations, an experimental rig was set up and used for ultrasound scanning of porcine tissue specimens. Findings from simulations were used to explore the applicability of the ultrasonic tracker to distal femoral fracture surgery, as well as other particular orthopaedic surgeries of relevance.

The research has led to the development of a comprehensive, generative 2-D simulation model that accounts for muscle fibres, fascicles and whole muscle structures. The model was used to simulate ultrasound scans, to track relative tissue movement and to assess coherence. The combined accuracy of optical tracking and ultrasonic tracking was quantified, shedding light on the applicability of such a method. Under the simulated conditions, a potentially viable solution for tracking the femur in distal femoral fracture surgery was proposed; a claim supported by the concluding region of interest plots.

Date of Award	27 Mar 2024
Original language	English
Awarding Institution	University of Bath
Supervisor	Ioannis Georgilas (Supervisor) & Alan Hunter (Supervisor)