Ultrasonic imaging and cortical thickness determination of long bones

• Author / Creator

  Zheng, Rui

• Osteoporosis is a bone disease characterized by the degradation of mechanical competence and support of the skeleton, leading to fracture risk of the wrist, vertebrae, and hip. The disease is due to major decrease of mass and deterioration of micro-structure of bone tissues.
  In this study, bone imaging methodologies are developed to image the internal structure of long bones and to estimate particularly the top cortical thickness using zero-offset data acquired on the bone surface. The inversion algorithm, which requires a background velocity model, is based on Born scattering theory implemented with conjugate gradient iterative method to seek an optimal solution. In case the velocity model is multilayered, ray tracing through a smooth medium will be used to calculate the travelled distance and travelling time. Using the simulated data, the forward and adjoint operators of the inversion method are validated for its feasibility, accuracy, and quality of the reconstructed images. The values of some inversion variables, such as frequency range, frequency sampling rate, beam aperture, source wavelet, noise level, temporal sampling interval, pixel size, spacing interval of acquisition, and inversion regularization, are also investigated to optimize the quality of the reconstructed images.
  To image the top cortical layer, a good estimate of the background velocity can be obtained by linear regression method using the offset axial transmission data. The inversion algorithm is applied to image four real bone samples in vitro. The results demonstrate the top cortical interfaces can be reconstructed and correspond favorably to the CT image. The measurements show the sectional mean thickness (SMT) is a better and robust estimate for the average thickness of the cortex. The thicknesses of the bovine, cervine and ovine samples are 5, 4 and 3 mm, respectively, which correspond to absolute errors of 1.9%, 4.6% and 3.2% in comparison with the CT images.
  
  Due to the tissue absorption, interface curvature, and local heterogeneities, imaging the other interfaces was less successful. However, the current imaging method has successfully recovered the top cortical layer, offering a potential diagnostic tool to estimate cortical thinning for osteoporosis assessment.

• Subjects / Keywords

  • Cortical bone
  • Born appoximation
  • Ultrasound velocity
  • Cortical thickness
  • Osteoporosis
  • Inversion
  • Ultrasonic imaging

• Graduation date

  Fall 2011

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R32P9S

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.