OTD range from external data.

Background and aim
Calibrated pelvic X-ray images are needed in the preoperative planning of total hip arthroplasty (THA) to predict component sizes. Errors and mismatch in the size of one or more components are reported, which can lead to clinically relevant complications. Our aim is to investigate whether we can solve the fundamental problem of X-ray calibration and whether traditional X-ray still has a place in preoperative planning despite improved radiological alternatives.
Methods
Based on geometric and radiographic principles, we estimate that the magnification factor is adapted to the X-ray device and depends strongly on the source-image distance of the device. We analyse the errors of the various calibration methods and investigate which narrow range can be expected to show that the center of rotation is sufficiently accurate. Based on the results of several CT-scans we defined an adapted magnification factor and validated the degree of measurement accuracy.
Results
The true magnification of objects on X-ray images depends mainly on the device settings. Stem size prediction is possible to a limited extent, with an error margin of 4.3%. Components can be predicted with a safety margin of one size up and down as with CT or 3D images. The prerequisite is that the source-image distance is greater than or equal to 120 cm, the table-image distance is known, and the object-image distance is estimated according to the patient’s BMI. We defined a device-adapted magnification factor that simplifies the templating routine and can be used to obtain the most reliable preoperative dimensional measurements that can be expected from X-ray images. We found the error margin of the magnification factor with the highest degrees of prediction and precision.
Conclusion
Preoperative planning is reliable and reproducible using X-ray images if calibration is performed with the device-adapted magnification factor suggested in this paper.

研究背景与目的
全髋关节置换术（total hip arthroplasty, THA）的术前规划需使用校准后的骨盆X线影像，以预测假体型号。已有研究显示，单个或多个假体的尺寸存在误差与匹配不当问题，可引发具有临床意义的并发症。本研究旨在解决X线影像校准这一核心问题，并探究尽管放射学检查手段已取得进步，传统X线检查在术前规划中是否仍具备应用价值。

研究方法
基于几何学与放射影像学原理，我们认为放大倍率需适配X线设备，且与设备的源片距密切相关。本研究分析了多种校准方法的误差，并探究可确保旋转中心测量足够精准的误差范围区间。基于多例CT扫描结果，我们确定了适配型放大倍率，并验证了其测量精准度。

研究结果
X线影像中物体的实际放大倍率主要取决于设备参数设置。股骨柄假体的型号预测具备一定可行性，误差范围为4.3%。与CT或三维影像类似，假体型号可通过±1个型号的安全裕度进行预测。该方法的前提条件为：源片距≥120cm、已知台片距，并根据患者身体质量指数（Body Mass Index, BMI）估算物片距。我们提出了设备适配型放大倍率，可简化术前模板规划流程，用于获取X线影像所能提供的最可靠术前尺寸测量结果。本研究明确了具备最优预测性能与精准度的放大倍率误差范围。

研究结论
若采用本研究提出的设备适配型放大倍率进行校准，利用X线影像开展的术前规划具备可靠性与可重复性。