Contrast and Velocity Ultrasonic Tomography of Long Bones

• Published in: Ultrasonic imaging Vol. 24; no. 3; pp. 139 - 160
• Main Authors: Ouedraogo, E., Lasaygues, P., Lefebvre, J.P., Gindre, M., Talmant, M., Laugier, P.
• Format: Journal Article
• Language: English
• Published: Los Angeles, CA SAGE Publications 01.07.2002; Dynamedia
• Subjects: Acoustical measurements and instrumentation; Acoustics; Biological and medical sciences; Elasticity; Exact sciences and technology; Feasibility Studies; Femur - diagnostic imaging; Fundamental areas of phenomenology (including applications); Humans; Image Processing, Computer-Assisted; Investigative techniques, diagnostic techniques (general aspects); Medical sciences; Miscellaneous. Technology; Phantoms, Imaging; Physics; Tomography; Ultrasonic investigative techniques; Ultrasonography - methods; Bone; velocity; refraction; reflection; ultrasound tomography; ray path; Human; Acoustic measurement; Experimental study; Born approximation; Wave reflection; Inverse problem; Osteoarticular system; Wave refraction; Tomography; Ray tracing; Signal processing; Acoustic image; Radon transformation; Cortical bone; Contrast media; Quantitative analysis
• ISSN: 0161-7346; 1096-0910
• DOI: 10.1177/016173460202400302

Our objective is to derive quantitative sound speed images of cortical bone using ultrasonic transmission tomography. Cortical bone is a highly refracting medium, i.e., the sound velocity changes abruptly across the interface between soft tissue and bone. It results in a loss of data compared to classical tomography in soft tissues. In order to correct for degradation by refraction effects, the classical acquisition procedure of projection data is modified; the transducers are oriented according to Snell's law of refraction with the aim of optimizing the sound propagation as parallel longitudinal rays inside the bone. This strategy allows the subsequent application of straight-ray reconstruction by the backprojection technique, which is a classical procedure in x-ray tomography. The method is validated with Plexiglas® solid cylinders and tubes immersed in water. Improved sound velocity images are then derived using conventional Radon transform of the experimental time-of-flight data. The method is then extended to in vitro human femur immersed in water. The geometry of the bone cross-section is reconstructed from measurements using ultrasonic reflection tomography. The result is then introduced in the calculation of the position and orientation of the transducers, which are associated with the parallel acoustical paths in bone in the transmission measurements. The procedure leads to significant restoration enhancement over the non corrected image. The mean value of the velocity of 3,200 ms−1 in the cortical shell is consistent with the values known from literature. These preliminary quantitative images using combined reflected and transmission ultrasound show promise for bone imaging.