INFLUENCE OF MARROW ON ULTRASONIC VELOCITY AND ATTENUATION IN BOVINE TRABECULAR BONE

Measurements of ultrasonic velocity and specific differential attenuat ion (SDA) were obtained on 24 bovine trabecular bone specimens from th e femoral condyles. The measurements were obtained using two pairs of ultrasonic transducers, one with a low nominal center frequency (500 k Hz) and the other pair with a high nominal center frequency (1 MHz). T he ultrasonic velocity and specific differential attenuation associate d with the bone samples were determined both with and without marrow, i.e., replacing the marrow with water in the pores of the trabecular b one. Significant increases (2.1% and 2.9%) in the velocity of ultrasou nd were observed after removal of the marrow, for the low and high fre quency transducer pairs, respectively. In contrast, significant decrea ses (-6.5% and -8.8%) in SDA were observed after removal of the marrow , for the low and high frequency transducer pairs, respectively. The b one densities (BD) of the samples were also determined using single ph oton absorptiometry (SPA). Correlations between ultrasonic parameters and bone densities for samples both with and without marrow were found to be similar. For example, for the 1 MHz transducer pair, the correl ation between BD and velocity was r = 0.86 with marrow, and r = 0.89 w ithout marrow. This study also compared the results obtained using a c ontact (no water bath) technique and an insertion (with a water bath) technique of ultrasonic measurements. For the high frequency transduce r pair, the correlation coefficients between the two methods were r = 0.99 and r = 0.93, for the velocity and specific differential attenuat ion, respectively. Similar results were found for the low frequency tr ansducer pair as well. In addition, approximately equal correlations b etween BD and ultrasonic velocity and SDA were also found, indicating that contact and insertion measurements provide essentially equivalent information.