Abstract

Background: Ultrasound transit time spectroscopy (UTTS) has been introduced previously to characterize the propagation of ultrasound waves through complex structures such as cancellous bone to estimate bone quality and quantity. UTTS describes the propagation of ultrasonic waves through a medium with two components of differing sound speeds (e.g., bone and marrow) as a set of parallel sonic rays. The transit time spectrum (TTS) is derived via the digital deconvolution of the input and output signals. The aim of the study is to investigate the dependence of TTS upon the type of ultrasound input wave, including four different 1 MHz ultrasound waves (pulse, chirp, tone-burst, and continuous).
Methods: Ten replica 3D- acrylic step-wedge models with different structure complexity were investigated. For each model and using the four types of input waves, TTS was derived and compared with calculated TTS based on the parallel sonic ray concept. 
Results: The results showed coefficients of determination (R²) of 0.994, 0.999, 0.90, and 1 for pulse, chirp, tone-burst and continuous signals respectively. Furthermore, solid volume fraction (SVF) was derived via TTS (TTS-SVF) and compared with the geometrically calculated SVF data of the models, yielding coefficients of determination (R²) of 0.941, 0.968, 0.489, and 0.981 for pulse, chirp, tone-burst and continuous waves, respectively. Therefore, the continuous wave provided a more accurate prediction of TTS and SVF, followed by chirp, then pulse waves.
Conclusion: This study adds to the body of research supporting the validity and reliability of UTTS, as a potentially promising technique to provide a reliable in vivo estimate of bone mineral density.

Keywords

Ultrasound, Transit time spectroscopy, Ultrasound propagation, Composite media, Deconvolution.

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