Modality-Independent Determination of Vertebral Position and Rotation in 3D
The determination of the position and rotation of vertebrae is important for the understanding of normal and pathological spine anatomy. Existing techniques, however, estimate the position and rotation parameters from two-dimensional (2D) planar cross-sec
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Abstract. The determination of the position and rotation of vertebrae is important for the understanding of normal and pathological spine anatomy. Existing techniques, however, estimate the position and rotation parameters from two-dimensional (2D) planar cross-sections, are relatively complex and require a relatively large amount of manual interaction. We have developed an automated and modality-independent method for the determination of the position and rotation of vertebrae in three dimensions (3D) that is based on registration of image intensity gradients, extracted in 3D from symmetrical vertebral parts. The method was evaluated on 52 vertebrae; 26 were acquired by computed tomography (CT) and 26 by magnetic resonance (MR). The results show that by the proposed gradient-based registration of symmetrical vertebral parts, the position and rotation of vertebrae in 3D can be successfully determined in both CT and MR spine images. As the position and rotation of vertebrae in 3D are among the most important spine parameters, the proposed method may provide valuable support in the evaluation of deformities and disease processes that affect the spine.
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Introduction
The determination of the position and rotation of individual vertebrae is important for the understanding of the nature of normal and pathological spine anatomy. The Cobb technique [1] is the most established method for measuring vertebral rotation from two-dimensional (2D) radiographic images of the spine in cases of scoliotic [2,3,4] and kyphotic/lordotic deformities [5,6,7,8]. Techniques that exploit the information from three-dimensional (3D) images, such as computed tomography (CT) and magnetic resonance (MR) images, were also proposed [9,10,11,12,13,14] and further combined with low level [2,3,8,15] and also more sophisticated image analysis methods [16,17,18]. Rogers et al. [16] measured axial vertebral rotation by registering circular areas in two MR axial cross-sections. The vertebral pose was determined by registering statistical shape models of vertebrae to presegmented vertebral bodies in stereoradiographic images in the study of Benameur et al. [17]. Adam and Askin [18] defined axial vertebral rotation as the axis of maximum symmetry in axial CT cross-sections. The vertebral center of rotation, located in the mid-sagittal plane at the anterior wall of the vertebral canal [19] and at the superior vertebral endplate [20], was T. Dohi, I. Sakuma, and H. Liao (Eds.): MIAR 2008, LNCS 5128, pp. 89–97, 2008. c Springer-Verlag Berlin Heidelberg 2008
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inherently included in the estimation of vertebral rotation. Although the aforementioned methods aimed to exploit the information in 3D, the measurements were still performed in 2D cross-sections, required a relatively high number of parameters and a relatively large amount of manual interaction. Besides manual determination of the center of rotation, the cross-sections were manually selected either from the original images or, to reduce the effect of virtual rotation [11,14] and verteb
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