Zappa U, Simona C, Graf H, van Aken J
Department of Periodontology, School of Dental Medicine, University of Bern, Switzerland.
J Periodontol. 1991 Nov;62(11):674-83. doi: 10.1902/jop.1991.62.11.674.
Subtraction radiography requires radiographs made with identical projection geometry. The purpose of the present investigation was to develop and evaluate a new in vivo method to measure angular radiographic projection error. This included the development of a system for accurate control of the x-ray beam angulation relative to the intraoral film and the evaluation of the in vivo projection errors (equivalent to the "angular difference" between repeated exposures) produced by the new system. A filmholder, an x-ray beam manipulator, and an aiming device were newly constructed. Reference wires were attached for measuring the projection error on the filmholder and on the 22 bicuspids at the sites of investigation in 16 patients. Two exposures using standardized projection conditions were made of each site. The relative position of the reference wires on the duplicate radiographs was used to calculate the angular difference in the direction of the x-ray beam which occurred between the 2 exposures. Triplicate measurements allowed the determination of measurement error. The angular projection errors were measured in a horizontal and vertical direction. The reference wires allowed determination of the angular projection errors relative to the filmholder, relative to the dentition and the angular error due to the repositioning of the filmholder in the patient's mouth. The average projection errors deviated only slightly from zero. The largest deviation registered was -0.11 degrees. This applies to the horizontal and vertical direction and all relationships. The standard deviations varied between 0.403 degrees and 0.697 degrees. This applies to the standard deviation for all relationships in the horizontal, the vertical, and the oblique directions. The measuring error found from the triplicate measurements had a standard deviation of 0.08 degrees to 0.19 degrees depending on the distance between the reference wires. This new system for controlling in vivo projection errors seems to provide highly standardized radiographs in vivo. The new measuring system proved to be accurate enough to measure the in vivo projection errors between repeated radiographs produced with the new filmholder and x-ray beam manipulator. The in vivo errors produced by the new system are markedly smaller than all in vivo and in vitro errors previously reported in the literature.
减影放射摄影需要使用相同投影几何结构拍摄的X线片。本研究的目的是开发并评估一种新的体内测量角度放射摄影投影误差的方法。这包括开发一种用于精确控制X射线束相对于口内胶片角度的系统，以及评估该新系统产生的体内投影误差（相当于重复曝光之间的“角度差异”）。新构建了一个胶片夹、一个X射线束操纵器和一个瞄准装置。在16名患者的研究部位，在胶片夹和22颗双尖牙上附着参考线以测量投影误差。每个部位使用标准化投影条件进行两次曝光。利用重复X线片上参考线的相对位置来计算两次曝光之间X射线束方向上的角度差异。进行三次测量以确定测量误差。在水平和垂直方向测量角度投影误差。参考线可确定相对于胶片夹、相对于牙列的角度投影误差以及由于胶片夹在患者口腔中重新定位导致的角度误差。平均投影误差仅略微偏离零。记录到的最大偏差为-0.11度。这适用于水平和垂直方向以及所有关系。标准差在0.403度至0.697度之间变化。这适用于水平、垂直和倾斜方向上所有关系的标准差。根据参考线之间的距离，三次测量得出的测量误差标准差在0.08度至0.19度之间。这种用于控制体内投影误差的新系统似乎能在体内提供高度标准化的X线片。新的测量系统被证明足够精确，能够测量使用新胶片夹和X射线束操纵器产生的重复X线片之间的体内投影误差。新系统产生的体内误差明显小于文献中先前报道的所有体内和体外误差。
