Rudolph D J, White S C, Mankovich N J
University of California at Los Angeles School of Dentistry.
Oral Surg Oral Med Oral Pathol. 1987 Nov;64(5):631-7. doi: 10.1016/0030-4220(87)90074-0.
In the course of digital subtraction radiography (DSR), variation in the alignment of the x-ray source object and image receptor is an undesirable but frequent problem. The influence of angulation changes between the x-ray source and object on the quality of the subtracted image was measured with the visualization of a thin chip of bone (thickness less than or equal to 0.85 mm). Twenty radiographic image pairs that differed by known geometric distortions ranging from 0 to 9 degrees horizontal and vertical were subtracted. The ability to detect a thickness change varied strongly with angular distortion. Under optimal conditions (no distortion), DSR was able to detect a change in thickness of cortical bone of 0.12 mm. Under approximately clinical circumstances (3 degree misalignment), a thickness change of 0.35 mm was detected with 50% accuracy (three of six cases), while a thickness change of 0.42 mm was detected with 100% accuracy (six of six cases). In addition, the influence of exposure parameters on DSR was investigated. Twenty-one radiographic film pairs were subtracted with differing densities and contrasts. Images made at 70 kVp with an optical density of 0.61 in the dentin produced the best subtracted images. However, even images made with one fourth the conventional exposure produced diagnostic information when analyzed with DSR; this was not seen with conventional analysis of the normally exposed radiographic films.
在数字减影血管造影（DSR）过程中，X射线源、物体和图像接收器的对准变化是一个不良但常见的问题。通过可视化一块薄骨片（厚度小于或等于0.85毫米）来测量X射线源与物体之间的角度变化对减影图像质量的影响。对20对因水平和垂直方向上已知几何失真（范围从0到9度）而不同的射线图像进行了相减处理。检测厚度变化的能力随角度失真而有很大差异。在最佳条件下（无失真），DSR能够检测到皮质骨厚度0.12毫米的变化。在大约临床情况下（3度错位），能以50%的准确率（6例中的3例）检测到0.35毫米的厚度变化，而能以100%的准确率（6例中的6例）检测到0.42毫米的厚度变化。此外，还研究了曝光参数对DSR的影响。对21对具有不同密度和对比度的射线胶片进行了相减处理。在牙本质中光学密度为0.61、70千伏峰值下拍摄的图像产生了最佳的减影图像。然而，即使是用常规曝光四分之一的曝光量拍摄的图像，在通过DSR分析时也能产生诊断信息；而对正常曝光的射线胶片进行常规分析时则看不到这一点。
