Purpose: In the last decades, the increasing medical interest in magnetic resonance imaging (MRI) of the spine gave rise to a growing number of publications on computerized methods for spine analysis, covering goals such as localization and segmentation of vertebrae and intervertebral discs as well as the extraction and segmentation of the spinal canal and cord. We provide a critical systematic review to work in the field, putting focus on approaches that can be applied to different imaging sequences and settings.
Methods: Work is analysed on two levels. First, methods are reviewed in detail so that the reader understands justifications and constraints of particular work. Second, work is classified according to relevant attributes and tabulated to give an impression on recent trends. We discuss the general methodical and evaluational aspects of the work as well as challenges specific to MRI such as the lack of intensity standardization and partial volume effects.
Results: Methods can be condensed to a small number of optimization frameworks, e.g., graphical models, cost-minimal paths and deformable models. Works sharing the same framework mainly differentiate by the types of information, i.e., pose, geometry and appearance, that are used and by the implementation thereof. MRI-specific challenges are rarely addressed explicitly, calling into question the applicability of most methods to changing imaging sequences or settings. Most often, little attention is paid to evaluation, meaning that results lack comparability and reproducibility although publicly available data sets exist.
Conclusion: The diversity of MRI sequences and settings still poses challenges to computerized spine analysis. Further research is necessary to implement methods that are actually applicable in practice, e.g., in clinical routine or for study purposes. Certainly, manual guidance will be necessary at some point, for instance to deal with changing subject positions. Therefore, future work should put attention to the appropriate integration of manual interaction.
Keywords: Extraction; Localization; Magnetic resonance imaging; Segmentation; Spine analysis.