Ultrasonic computed tomography based on full-waveform inversion for bone quantitative imaging.

Area of Science:

• Biomedical Engineering
• Medical Imaging
• Acoustics

Background:

• Quantitative imaging of long bones is crucial for diagnosing and monitoring skeletal diseases.
• Traditional imaging methods have limitations in assessing bone microstructure and mechanical properties.
• Ultrasonic imaging offers a non-invasive and radiation-free alternative.

Purpose of the Study:

• To develop and validate an ultrasonic quantitative imaging method for long bones.
• To apply full-waveform inversion (FWI) for enhanced bone imaging.
• To assess the method's performance on benchmark models and a human tibia-fibula pair.

Main Methods:

• Utilized a 2D acoustic approximation for computational efficiency.
• Employed a quasi-Newton optimization technique (Limited-memory Broyden-Fletcher-Goldfarb-Shanno) for iterative inversion.
• Defined the cost function based on L²-norm difference between observed and synthetic data.

Main Results:

• Successfully imaged single and multiple cylinders, demonstrating robustness against multiple diffraction effects.
• Generated quantitative images of a tibia-fibula bone pair.
• Achieved fast convergence, typically within 15-30 iterations per frequency band.

Conclusions:

• The developed ultrasonic FWI method is effective for quantitative imaging of long bones.
• Strategies to mitigate the 'cycle skipping' artifact were discussed and illustrated.
• Future work will focus on viscoelastic models and real-world data acquisition.