Comparison of conventional transducer and refracto-vibrometry measurements of ultrasonic transmission parameters from heel bones

Abstract

Ultrasonic measurements of the heel bone (calcaneus) are used commonly for osteoporosis screening. Ultrasound pulses that pass through the calcaneus are detected with a receiving transducer. Parameters, such as normalized broadband ultrasound attenuation (nBUA) and speed of sound (SOS) calculated from the wave forms detected by the receiving transducer, are utilized to assess bone health. In the current study, refracto-vibrometry (RV), an interferometric method for optically measuring ultrasound, was compared with conventional transducer measurements of ultrasound transmission in-vitro through a human calcaneus sample. The measurement beam from a Polytec PSV-400 scanning laser Doppler vibrometer was directed through a water tank towards a stationary retroreflective surface. Acoustic wave fronts (density variations) which pass through the ~50μm diameter measurement laser cause variations in the integrated optical path length. The signals detected by the vibrometer at numerous scan points were used to determine the time evolution of ultrasonic wave fronts. Because there is not a physical receiving transducer, the RV measurements do not experience the same frequency response and reflection artifacts of conventional transducers. Parameters such as nBUA and SOS were calculated at multiple RV scan points, and the results were compared to parameters measured using a conventional ultrasound transducer.Ultrasonic measurements of the heel bone (calcaneus) are used commonly for osteoporosis screening. Ultrasound pulses that pass through the calcaneus are detected with a receiving transducer. Parameters, such as normalized broadband ultrasound attenuation (nBUA) and speed of sound (SOS) calculated from the wave forms detected by the receiving transducer, are utilized to assess bone health. In the current study, refracto-vibrometry (RV), an interferometric method for optically measuring ultrasound, was compared with conventional transducer measurements of ultrasound transmission in-vitro through a human calcaneus sample. The measurement beam from a Polytec PSV-400 scanning laser Doppler vibrometer was directed through a water tank towards a stationary retroreflective surface. Acoustic wave fronts (density variations) which pass through the ~50μm diameter measurement laser cause variations in the integrated optical path length. The signals detected by the vibrometer at numerous scan points were used to deter...