[Unsharpness of redundant shadows of the mandibular ramus region in panoramic tomography. The influence by the first slit width].

Shika gakuho. Dental science reports Pub Date : 1990-04-01
M Wakoh, H Ueno, K Yamamoto, K Harada, K Kuroyanagi
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Abstract

In panoramic tomography, redundant shadows of the mandibular ramus overlapping with tomographic images on the opposite side prevent radiological diagnosis. Redundant shadows differ from tomographic images in sharpness, film contrast, and imaging quality. In addition to mismatching of film velocities and X-ray beams, familiar causes of such unsharpness, still another source must be taken into consideration: the influence of varying slit widths. In the past, research has been concentrated on real images defined by McDavid et al.; that is, tomographic images and tomographic blurring images. The present study, however, qualitatively evaluates the unsharpness of redundant shadows of the mandibular ramus, especially with reference to the effects of first-slit width. At the same time, comparisons are made with tomographic images overlapping with redundant shadows of the mandibular ramus region. An orthopantomograph OP5 was employed as the panoramic X-ray apparatus. In the first step of the evaluation, X-ray beam alignments were examined in the horizontal dimension. To evaluate unsharpness of the mandibular ramus, we used regression analysis by the least-squares method and the Nitka method. Horizontal beam alignments and image layers as calculated by McDavid et al. (1985) were applied in setting the aluminum plate. Conclusions 1. In the case of redundant shadows of the mandibular ramus, unsharpness of the posterior margin and the condylar process depends on first-slit width, which is a major influence on imaging quality. 2. Intensity of edge and film contrast exert about equal influences on unsharpness of redundant shadows of the mandibular ramus. Both factors were influenced by the set-up position of the subject. 3. Film contrast exerted a greater influence than edge intensity on unsharpness of overlapped tomographic images. 4. The wider the first-slit width, the greater the indistinct area of redundant shadows of the mandibular ramus and overlapped images. But, for the purposes of diagnosis, maximum slit width is probably between 3 and 5 mm.

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全景断层扫描下颌支区冗余阴影不清晰。第一狭缝宽度的影响]。
在全景断层扫描中,下颌分支的冗余阴影与对侧的断层图像重叠妨碍放射诊断。冗余阴影在清晰度、胶片对比度和成像质量上与层析成像图像不同。除了胶片速度和x射线光束的不匹配(这是造成这种不锐利的常见原因)之外,还必须考虑另一个来源:不同狭缝宽度的影响。过去,研究主要集中在McDavid等人定义的真实图像上;即层析成像和层析模糊成像。然而,本研究定性地评价了下颌分支冗余阴影的不清晰度,特别是参考了第一狭缝宽度的影响。同时,与重叠的下颌分支区域的冗余阴影层析图像进行了比较。全景式x线仪采用OP5型正骨解剖仪。在评估的第一步,x射线束对准在水平维度进行了检查。为了评估下颌支的不锐度,我们采用最小二乘法和Nitka方法进行回归分析。采用McDavid等人(1985)计算的水平光束对准和图像层来设置铝板。结论1。在下颌支阴影过多的情况下,后缘和髁突的不锐度取决于第一狭缝宽度,这是影响成像质量的主要因素。2. 边缘强度和胶片对比度对下颌分支冗余阴影的不锐度影响大致相等。这两个因素都受到被试设置位置的影响。3.胶片对比度比边缘强度对重叠层析图像不锐度的影响更大。4. 第一狭缝宽度越宽,下颌分支的冗余阴影和重叠图像的模糊区域越大。但是,为了诊断的目的,最大狭缝宽度可能在3到5毫米之间。
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