Purpose: Measurement of global spinal alignment (GSA) is an important aspect of diagnosis and treatment evaluation for spinal deformity but is subject to a high level of inter-reader variability.
Approach: Two methods for automatic GSA measurement are proposed to mitigate such variability and reduce the burden of manual measurements. Both approaches use vertebral labels in spine computed tomography (CT) as input: the first (EndSeg) segments vertebral endplates using input labels as seed points; and the second (SpNorm) computes a two-dimensional curvilinear fit to the input labels. Studies were performed to characterize the performance of EndSeg and SpNorm in comparison to manual GSA measurement by five clinicians, including measurements of proximal thoracic kyphosis, main thoracic kyphosis, and lumbar lordosis.
Results: For the automatic methods, 93.8% of endplate angle estimates were within the inter-reader 95% confidence interval (CI95). All GSA measurements for the automatic methods were within the inter-reader CI95, and there was no statistically significant difference between automatic and manual methods. The SpNorm method appears particularly robust as it operates without segmentation.
Conclusions: Such methods could improve the reproducibility and reliability of GSA measurements and are potentially suitable to applications in large datasets—e.g., for outcome assessment in surgical data science.
Intraoperative imaging systems are seeing an increased role in support of surgical guidance and quality assurance in the operating room for interventional approaches. However, image quality sufficient to detect complications and provide quantitative assessment of the surgical product are often confounded by image noise and artifacts. In this work, we translated a 3D image reconstruction method (referred to as “Known-Component Reconstruction,” KC-Recon) for the first time to clinical studies with the aim of resolving both limitations. KC-Recon builds upon an optimization-based reconstruction method to reduce noise and incorporates a model of surgical instruments in the image to reduce artifacts. The first clinical pilot study involved 17 spine surgery patients imaged using the O-arm before and after spinal instrumentation. Imaging performance was evaluated in terms of low-contrast soft-tissue visibility, the ability to assess screw placement within bone margins, and the potential to image at lower radiation doses. Depending on the imaging task, dose reduction up to an order of magnitude appeared feasible while maintaining soft-tissue visibility. KC-Recon also yielded ~30% reduction in blooming artifact about the screw shafts and ~60% higher tissue homogeneity at the screw tips, providing clearer depiction of pedicle and vertebral body for assessment of potential breaches. Overall, the method offers a promising means to reduce patient dose in image-guided procedures, extend the use of cone-beam CT to soft-tissue surgeries, provide a valuable check against complications in the operating room (cf., post-operative CT), and serve as a basis for quantitative evaluation of quality of the surgical construct.
Purpose: A method for automatic computation of global spinal alignment (GSA) metrics is presented to mitigate the high variability of manual definitions in radiographic images. The proposed algorithm segments vertebral endplates in CT as a basis for automatic computation of metrics of global spinal morphology. The method is developed as a potential tool for intraoperative guidance in deformity correction surgery, and/or automatic definition of GSA in large datasets for analysis of surgical outcome. Methods: The proposed approach segments vertebral endplates in spine CT images using vertebral labels as input. The segmentation algorithm extracts vertebral boundaries using a continuous max-flow algorithm and segments the vertebral endplate surface by region-growing. The point cloud of the segmented endplate is forward-projected as a digitally reconstructed radiograph (DRR), and a linear fit is computed to extract the endplate angle in the radiographic plane. Two GSA metrics (lumbar lordosis and thoracic kyphosis) were calculated using these automatically measured endplate angles. Experiments were performed in seven patient CT images acquired from Spineweb and accuracy was quantified by comparing automatically-computed endplate angles and GSA metrics to manual definitions. Results: Endplate angles were automatically computed with median accuracy = 2.7°, upper quartile (UQ) = 4.8°, and lower quartile (LQ) = 1.0° with respect to manual ground-truth definitions. This was within the measured intra- observer variability = 3.1° (RMS) of manual definitions. GSA metrics had median accuracy = 1.1° (UQ = 3.1°) for lumbar lordosis and median accuracy = 0.4° (UQ = 3.0°) for thoracic kyphosis. The performance of GSA measurements was also within the variability of the manual approach. Conclusions: The method offers a potential alternative to time-consuming, manual definition of endplate angles for GSA computation. Such automatic methods could provide a means of intraoperative decision support in correction of spinal deformity and facilitate data-intensive analysis in identifying metrics correlating with surgical outcomes.
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