Background

A method to evaluate pedicle screw loosening on digital tomosynthesis images is yet to be established owing to lack of methods for selecting slices of the same cross-sectional view. We aimed to develop an objective method for selecting slices of the same cross-sectional view on digital tomosynthesis images.

Methods

First, an objective method of pixel selection was developed by measuring the size of glass disk and titanium alloy screw on digital tomosynthesis images followed by comparison with the actual sizes. Second, a method for selecting slices of the same cross-sectional view was explored on a bone model with posterior spinal instrumentation using the screw centerline and rod curvature as indicators of the same cross section. The angle between the screw centerline and rod was calculated to verify the accuracy in obtaining the same cross-sectional view. Third, the method for selecting slices of the same cross-sectional view was applied to six patients after posterior lumbar spinal instrumentation.

Results

The pixel selection method enabled objective determination of a pixel on the peripheral lines of objects with an error as low as 200 μm in distance measurements on titanium alloy and glass. The mean differences of rod-screw angles between two slices were less than 1° and were not statistically significant in the bone model and patient images.

Conclusion

A method for selecting slices of the same cross-sectional view on digital tomosynthesis images was successfully developed. This method can enable objective and quantitative evaluations of pedicle screw loosening.

中文翻译：

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从数字断层合成中选择相同横截面切片以监测后路脊柱器械的新方法

背景

由于缺乏选择相同横截面视图的切片的方法，尚未建立一种评估数字断层合成图像上椎弓根螺钉松动的方法。我们旨在开发一种客观方法，用于在数字断层合成图像上选择相同横截面视图的切片。

方法

首先，通过测量数字断层合成图像上的玻璃盘和钛合金螺钉的尺寸，然后与实际尺寸进行比较，开发了一种客观的像素选择方法。其次，使用螺钉中心线和杆曲率作为相同横截面的指标，在​​带有后路脊柱器械的骨模型上探索了一种选择相同横截面视图切片的方法。计算螺钉中心线和杆之间的角度以验证获得相同横截面视图的准确性。第三，选择相同横截面切片的方法应用于6例腰椎后路内固定术后的患者。

结果

在钛合金和玻璃的距离测量中，像素选择方法能够客观地确定物体外围线上的像素，误差低至200μm。两个切片之间的杆 - 螺钉角度的平均差异小于 1°，并且在骨模型和患者图像中没有统计学意义。

结论

成功开发了一种用于在数字断层合成图像上选择相同横截面视图的切片的方法。该方法可以对椎弓根螺钉松动进行客观和定量的评估。