DIFFRACTION AND INTERFACE LOSSES IN BROAD-BAND ULTRASOUND ATTENUATIONMEASUREMENTS OF THE CALCANEUM

Ultrasonic investigation of bone disease most frequently involves meas urements on the heel, and the parameter most often used for this is th e broadband ultrasound attenuation (BUA) which is the slope of the att enuation as a function of frequency between 0.2 and 0.6 MHz. In this s tudy, the possible losses in the BUA measurement due to diffraction an d interfaces have been discussed and evaluated using existing data and a standard diffraction model. The loss due to diffraction was found t o depend critically upon whether a contact or immersion technique is u sed. For a contact method, we estimate that the diffraction loss can b e greater than 10 dB MHz(-1), whereas insertion devices typically will have losses of up to 0.6 dB MHz(-1), and it not always clear whether or how manufacturers have attempted to correct for this. Dispersion wh ich is found in the os calcis has only a small effect on the diffracti on loss, but it can cause a frequency dependent interface loss of abou t 0.2 dB MHz(-1) It may be impossible to correct for these discrepanci es in vivo as the necessary data for the individual components of the heel are not known. However the losses should be borne in mind as fact ors limiting the accuracy of the measurements and, in the case of in v itro investigations, may merit further study.