Diagnosis of osteoporosis using the low frequency acoustic response of mice femoral bones irradiated by a high frequency acoustic radiation pulse

Quantitative characterization of the mechanical properties of bones is of great importance to diagnostic pathological processes. For example, osteoporotic bones have some differences in the mechanical properties if compared with the healthy ones. In this study a new technique based on acoustic radiation force has been used as an alternative to evaluate the differences in the mechanical properties of bones, that can lead to a new method to the diagnosis of bone diseases. The technique uses a single high-frequency ultrasound pulse (MHz) to excite the medium. Non-linear interactions of this acoustic wave in the tissue produces a lower frequency signal (kHz). Femoral bones where excised from 10 healthy mice and also from 10 mice where osteoporosis had been induced. Using µCT, the porosity, trabecular number, trabecular spacing, connectivity and the connectivity density of those bones where obtained. The following step was to irradiate those samples with a short focused acoustic radiation pulse (f=3.1 MHz, t=15 µs) and acquire the low frequency acoustic response using a dedicated hydrophone (ITC 6050) with acquisition band going from 1kHz to 70 kHz. A spectral analysis of the acquired signal has been done and the results compared with the µCT data in order to see if there where correlation between them. Also, a hypothesis test has been done to see if the technique can differentiate the samples coming from the healthy group and the osteoporotic. A strong correlation was obtained between the values from the spectral analysis of the low frequency acoustic response and from the trabecular number parameter µCT (spearman correlation coefficient of 0.72 and p-value of 0.02), also a moderate correlation has been found with the connectivity parameter ( spearman correlation coefficient of 0.69 and p-value of 0.03) showing that the technique is sensible to the mechanical parameters .