Introduction Magnification error is always present in radiography and calibration is necessary, if high accuracy is required in pre-surgical planning. The goal of this study was to verify the use of self-made markers and calibration techniques and to establish guidelines for magnification correction.

Methods We evaluated and compared spherical and linear markers of different sizes with focus on practicability, accuracy and precision. Markers were placed on foam pads or attached to flexible arms.

Results Vertical marker deviation of 1 cm from the anatomical reference point corresponded to ∼1% of magnification error in our setting. Marker placement along the horizontal plane showed no significant magnification in the periphery of the radiograph. All markers showed good accuracy and the commercial spherical marker with a flexible segment arm had the best results regarding practicability.

Discussion Our study suggests that marker type is not solely responsible for usability and accuracy but also the type of fixation. In the absence of a calibration marker, calculation of the magnification factor using a measurement tape during radiography is equally reliable. Use of a fixed averaged calculated calibration factor showed poor agreement compared with the marker calibration, probably due to variability in size of the animals. In conclusion, if precision matters, use of a calibration marker, which could be purchased or self-made, is advised.

简介 射线照相中总是存在放大误差，如果在术前计划中需要高精度，则必须进行校准。本研究的目的是验证自制标记和校准技术的使用，并建立放大校正指南。

方法 我们评估和比较了不同尺寸的球形和线性标记，重点关注实用性、准确性和精度。标记被放置在泡沫垫上或连接到柔性臂上。

结果 与解剖参考点 1 厘米的垂直标记偏差对应于我们设置中放大误差的 1%。沿水平面放置的标记在 X 射线照片的周边没有显示出明显的放大。所有标记都显示出良好的准确性，带有柔性分段臂的商用球形标记在实用性方面具有最佳效果。

讨论 我们的研究表明，标记类型不仅对可用性和准确性负责，而且对固定类型负责。在没有校准标记的情况下，在射线照相期间使用测量带计算放大系数同样可靠。与标记校准相比，使用固定的平均计算校准因子显示出较差的一致性，这可能是由于动物大小的可变性。总之，如果精度很重要，建议使用可以购买或自制的校准标记。