Reliability of Three-dimensional Ultrasound Parameters and Their Correlation with the Progression of Adolescent Idiopathic Scoliosis

  • Author / Creator
    Vo, Quang N
  • Adolescent idiopathic scoliosis (AIS) is a three-dimensional (3D) spinal deformity with unknown causes and with prevalence of 1.5 - 3% of adolescents. If AIS is left untreated, it may progress, leading to back pain, cardiopulmonary problems, and psychosocial concerns, and eventually resulting in surgical intervention. Four types of scoliosis treatment exist and the selection of management depends on the severity and the risk of progression. Currently, the Cobb angle is the gold standard to measure the severity of the spinal curvature on a two-dimensional (2D) postero-anterior (PA) radiograph. However, this 2D measurement may underestimate the true severity of scoliosis, which affects treatment decisions. To report the actual severity, the Cobb angle on the plane of maximum curvature (PMC) must be measured, requiring a 3D spinal image. Although X-ray based imaging modalities such as computed tomography (CT) and multi-planar radiography provide good 3D images of the spine, the cumulative amount of ionizing radiation increases the risk of cancer. Therefore, 3D ultrasound was proposed in this PhD research as an alternative imaging method to measure spinal severity. In addition to the Cobb angle, the axial vertebral rotation (AVR) and the lateral deviation were also measured from the ultrasound images. To reconstruct 3D spinal images from 2D B-scans (B-mode images), a software was developed using the voxel-based reconstruction method with bi-linear interpolation. This software could also measure the AVR, the Cobb angle and the lateral deviation on the PA plane and the PMC. In order to obtain an optimal reconstructed image, in-vitro and in-vivo experiments were performed to investigate the optimal ultrasound configurations that consisted of the ultrasound frequency, the minimum spacing between two adjacent B-scans, and the reconstruction resolution. From both in-vitro and in-vivo studies, it was recommended that the frequency of 2.5 MHz, the spacing of 0.2 mm, and the reconstruction resolution of 0.6 mm constituted the best results. To measure the AVR, the Cobb angle and the lateral deviation on the PA plane and the PMC, the centre-of-lamina method was used. In-vitro and in-vivo studies were performed and the results demonstrated that the intra- and inter-rater reliabilities were high for all five parameters (ICC > 0.90). In addition, the Cobb angle measurements from the PA ultrasound images agreed well with the Cobb angle measurements from scoliosis clinics with a small variation (MAD < 3 degrees) and high correlation (ICC > 0.90). The measurements of the lateral deviations also showed high reliabilities (ICC > 0.90 and MAD < 7 mm). Furthermore, the average difference between the PMC Cobb angle and the PA Cobb angle was 1.0 ± 1.0 degrees within the range of 0 and 7 degrees. This result agreed with reports from literature. In addition, the AVR from the in-vitro study showed a strong correlation and high agreement between the ultrasound and CT images (ICC > 0.90, MAD < 2 degrees). Unfortunately, the in-vivo intervertebral rotations reported from the EOS system did not match to the ultrasound measurements. Further studies will be required to understand the reasons for the discrepancies. Since the 3D ultrasound was able to provide true spinal deformity information, a study to investigate which demographic and 3D ultrasound parameters correlated with the progression of AIS was conducted. A preliminary predictive model was developed using multi-linear regression and 23 retrospective subjects’ data. The results demonstrated the PMC Cobb angle and the number of vertebrae within the largest curve were the most reliable predictors. A preliminary validation using 6 subjects was performed. The variation between the measured and the predicted Cobb angles was 2.9 ± 1.3 degrees. The adjusted r2 was 0.87, indicating a good fit of data to the model. In conclusion, this PhD thesis demonstrated that the 3D freehand ultrasound method could be used to reconstruct 3D images of the scoliotic spine. The AVR, the PMC Cobb angle and lateral deviation could be measure reliably to assess the true severity of AIS. The PMC Cobb angle and the number of vertebrae within the largest curve were the potential parameters that could be used to predict the progression of AIS.

  • Subjects / Keywords
  • Graduation date
    Fall 2016
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • 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.