Validation of 3D surface reconstruction of vertebrae and spinal column using 3D ultrasound data--a pilot study.

Adolescent idiopathic scoliosis (AIS) is a three-dimensional deformity of spine associated with vertebra rotation. The Cobb angle and axial vertebral rotation are important parameters to assess the severity of scoliosis. However, the vertebral rotation is seldom measured from radiographs due to time consuming. Different techniques have been developed to extract 3D spinal information. Among many techniques, ultrasound imaging is a promising method. This pilot study reported an image processing method to reconstruct the posterior surface of vertebrae from 3D ultrasound data. Three cadaver vertebrae, a Sawbones spine phantom, and a spine from a child with AIS were used to validate the development. The in-vitro result showed the surface of the reconstructed image was visually similar to the original objects. The dimension measurement error was <5 mm and the Pearson correlation was >0.99. The results also showed a high accuracy in vertebral rotation with errors of 0.8 ± 0.3°, 2.8 ± 0.3° and 3.6 ± 0.5° for the rotation values of 0°, 15° and 30°, respectively. Meanwhile, the difference in the Cobb angle between the phantom and the image was 4° and the vertebral rotation at the apex was 2°. The Cobb angle measured from the in-vivo ultrasound image was 4° different from the radiograph.