Noninvasive measurement of stiffness and density of bone for its diagnosis using ultrasound

Because the acoustic and elastic properties of bone evaluated using ultrasound-based methods have proved so useful in the direct evaluation of bone characteristics, many workers have developed methods and systems based on thein vivo measurement of velocity, attenuation, or both, of ultrasound in bone. These include the acoustic emission (AE), apparent velocity of ultrasound (AVU), and speed of sound-broadband ultrasound attenuation (SOS-BUA) methods. Bone stiffness is accepted as an effective index in the diagnosis of such bone diseases as osteoporosis. The literature contains reports of the estimation of bone stiffness from velocity (speed of sound [SOS]) and attenuation (broadband ultrasound attenuation [BUA]). The physical explanation of the methods of evaluating stiffness from the obtained values of BUA and SOS is still not clear, however. Here we propose a new diagnostic method and system based on ultrasound measurement of the stiffness of bone. The proposed method determines stiffness from the velocity of the leaky surface skimming compressional waves (LSSCWs) obtained with the microdefocusing method and the acoustic impedance obtained with the reflectance method. Thus this method can evaluate stiffness without exposing the patient to X-rays; moreover, the physical basis of the calculation of stiffness from velocity and impedance is well understood. We applied this system to the human tibiain vivo: stiffness and density in a young volunteer were successfully evaluated at 24.9 GPa and 2.01×10(3) kg/m(3), respectively.