A 3-D Ultrasound Tomography Method for Bone Morphology Evaluation

Accurately imaging bones using ultrasound has been a long-standing challenge, primarily due to the high attenuation, significant acoustic impedance contrast at cortical boundaries, and the unknown distribution of sound velocity. Furthermore, two-dimensional (2-D) ultrasound bone imaging has limitations in diagnosing osteoporosis from a morphological perspective, as it lacks stereoscopic spatial information. To address these limitations, a three-dimensional (3-D) bone ultrasound tomography (USCT) method was proposed in this work. The compensations of directivities for the emitting and receiving elements on artifact elimination were incorporated. Moreover, the application of acoustic reciprocity further reduced the amount of data storage and improved the efficiency of the method. Two ex-vivo bovine femurs were employed to demonstrate the effectiveness of the method for 3-D cortical bone reconstruction and osteoporosis diagnosis. The reconstructed 3-D images were in good agreement with the reference images scanned by micro computed tomography (mu CT) in terms of the volume. The mean relative errors of 3-D volumes for the ex-vivo experiments were all smaller than 13%. Unlike 2-D imaging, 3-D reconstruction can quantitatively provide the bone mass loss (i.e., 2.85% for sample 1 and 3.72% for sample 2, respectively), rather than simply offering a qualitative description of 2-D morphology of the osteoporosis part. The proposed bone USCT method has been demonstrated to be an effective way for 3-D cortical bone imaging and osteoporosis diagnosis.