Wunderlich W, Fischer F, Linderer T, Kirkeeide R L
Division of Cardiology, Klinikum Steglitz, Free University, Berlin, Germany.
Angiology. 1995 Jul;46(7):577-82. doi: 10.1177/000331979504600704.
Isocenter calibration transforms cardiac structures in digitized biplane angiograms to absolute dimensions, calculating their radiological magnification and video transformation. Since a scaling device is not required, isocenter calibration yields to more accurate measurements than the widely used reference object calibration. Both isocenter methods reported so far, regarding geometrically inaccurate x-ray gantries, yield to different and complex computational formulas. Since these formulas are hard to understand, isocenter calibration is less widely used. To facilitate the implementation of the isocenter calibration, the basic formulas for accurate x-ray gantries are derived. Shifting virtually one x-ray system onto the other, basic isocenter calibration is derived geometrically in three simple steps. The radiological magnification of an object is illustrated as a ratio of planes. The calculation of all parameters entering the computations is demonstrated geometrically, by use of the isocenter of the x-ray gantry. The derivation gives a clear idea of isocenter calibration. It is simple to derive and facilitates the understanding of the error regarding developments. When geometrical inaccuracies vanish, all formulas become equivalent. However, even if the inaccuracies increase, all methods provide nearly identical results, indicating the robustness of isocenter calibration.
等中心校准将数字化双平面血管造影中的心脏结构转换为绝对尺寸，计算其放射放大率和视频转换。由于不需要缩放设备，等中心校准比广泛使用的参考物体校准能产生更准确的测量结果。到目前为止报道的两种等中心方法，对于几何精度不准确的X射线机架，会产生不同且复杂的计算公式。由于这些公式难以理解，等中心校准的应用不太广泛。为便于等中心校准的实施，推导了精确X射线机架的基本公式。通过将一个X射线系统虚拟地移动到另一个上面，分三个简单步骤从几何角度推导出基本等中心校准。物体的放射放大率表示为平面的比率。通过使用X射线机架的等中心，从几何角度演示了进入计算的所有参数的计算。该推导对等中心校准给出了清晰的概念。它易于推导，有助于理解相关误差。当几何误差消失时，所有公式都变得等效。然而，即使误差增加，所有方法提供的结果也几乎相同，这表明等中心校准的稳健性。
