Microwave Imaging for Muscle Rupture Detection

Doktorsavhandling, 2024

Muscle injuries are common in sports like football, sprinting, and running, particularly affecting the hamstring muscles in the back of the thigh. Magnetic resonance imaging (MRI) is often used for diagnosis, but its high cost limits accessibility, leaving many patients without definitive diagnoses.

This work explores microwave imaging as an alternative for detecting muscle ruptures, offering a more affordable and accessible solution for earlier detection and better care. A microwave-based imaging system includes an antenna array, a measurement system, and an imaging algorithm. This research focuses on developing methods enabling design of a compact, low-cost system with repeatable and fast imaging capability.

In the first part of this study, measurement repeatability was investigated and improved using a monopole antenna with a lossy (conductive) gel to attenuate unwanted signals propagating outside the body. A software-defined radio (SDR) was also investigated as a low-cost, compact alternative to a Vector Network Analyzer (VNA). With a simple calibration strategy, the SDR achieved repeatability and accuracy down to more than -70 dB signal attenuation, proving it would be a viable option for muscle rupture detection.

The second part focused on reducing the measurement time while preserving imaging accuracy. The lossy gels in the antennas was found to improve the imaging accuracy, while a novel matched filter-based DMAS algorithm further improved the accuracy. This work also found that optimization of the number of measured transmission channels and measured frequency points enables faster measurements with minimal impact on image accuracy.

Finally, imaging experiments demonstrated that images could be successfully reconstructed with the SDR, combined with the DMAS algorithm.

In conclusion, this study provides the first proof of principle for a feasible, cost-effective microwave imaging system, offering a potential to further develop a portable alternative for muscle injury diagnostics.