Jensen T W, Goldberg A J, Randall G J
Oral Surg Oral Med Oral Pathol. 1981 Jun;51(6):653-61. doi: 10.1016/s0030-4220(81)80018-7.
An investigation of the resolution capability of conventional and "free focus" dental radiography on non screen film was completed. The over-all imaging performance of conventional and "free focus" radiography exposed with three types of dental x-ray machines was comparable. Conventional "long-cone" radiography produced better resolution than "short-cone" radiography. "Short-cone" radiography exposed with conventional compact dental x-ray machines provided similar or better image resolution than those exposed with larger, high-energy machines. The miniaturized dental x-ray machines used in "free focus" radiography for periapical type exposures gave a resolution which was similar to or up to 100 percent higher than in conventional "long-cone" periapical radiographs. Differences in path length of the x-ray beam during clinical applications of conventional and "free focus" radiography indicated a higher potential for image noise and degradation in conventional films. A potential for segmental variation in image resolution in surveys of the dentition was seen only in the conventional techniques. These characteristics must be balanced against a tendency to variable segmental magnification in free focus radiography. Indications, however, are that applications of "free focus" radiography may be able to improve the early diagnosis of dental disease. Periapical type surveys of the dentition produced by "free focus" radiography may require only two exposures instead of the 14 to 20 required in conventional periapical surveys and may contain characteristics of periapical as well as bitewing films. "Free focus" radiography represents an attractive alternative that may be able to accomplish substantial time savings in the practice of dental radiography.
一项关于传统牙科X线摄影与“自由聚焦”牙科X线摄影在非增感屏胶片上分辨率能力的研究已经完成。使用三种类型牙科X线机进行曝光的传统牙科X线摄影与“自由聚焦”牙科X线摄影的总体成像性能相当。传统的“长锥形”牙科X线摄影比“短锥形”牙科X线摄影具有更好的分辨率。使用传统紧凑型牙科X线机进行“短锥形”牙科X线摄影所提供的图像分辨率，与使用更大的高能牙科X线机进行“短锥形”牙科X线摄影时相似或更高。用于“自由聚焦”牙科X线摄影根尖周类型曝光的小型化牙科X线机所产生的分辨率，与传统“长锥形”根尖周X线片的分辨率相似，或比其高出100%。在传统牙科X线摄影和“自由聚焦”牙科X线摄影的临床应用过程中，X线束路径长度的差异表明传统胶片产生图像噪声和图像质量下降的可能性更高。只有在传统技术中，才会在牙列检查中出现图像分辨率的节段性差异。这些特性必须与“自由聚焦”牙科X线摄影中节段性放大率变化的趋势相权衡。然而，有迹象表明，“自由聚焦”牙科X线摄影的应用可能能够改善牙科疾病的早期诊断。由“自由聚焦”牙科X线摄影产生的牙列根尖周类型检查可能只需要两次曝光，而不是传统根尖周检查所需的14至20次曝光，并且可能包含根尖周片和咬合翼片的特征。“自由聚焦”牙科X线摄影是一种有吸引力的替代方法，在牙科X线摄影实践中可能能够大幅节省时间。
