Borasi G, Berardi P, Ferretti P P, Piccagli V
Servizio di Fisica Sanitaria, Arcispedale S. Maria Nuova, USL n. 9, Reggio Emilia.
Radiol Med. 1990 Sep;80(3):339-46.
Comparative evaluation of radiographic film-screen systems presents several problems from both the theoretical and the experimental point of view. From the theoretical point of view the main difficulties are related to the choice of the parameters best suited to express the "overall quality" of a system. From the practical point of view the main problem is that to measure some basic quantities (resolution and noise) sophisticated and expensive instruments are required. This paper deals with both these problems. To express image quality we have assumed the signal-to-noise power ratio: this index depends in a explicit way on contrast, resolution and noise of the system. The dependence on sensitivity is implicit and was derived using literature data. From a knowledge of the dependence of image quality on sensitivity it is possible to develop an "overall quality" index which is considered to express the "technological level" of the system. This index can be used in the comparative evaluation of the different systems. In this work some basic physical quantities (characteristic curve, sensitivity) were evaluated using standard instruments. To measure spatial resolution and noise an inexpensive, PC-based, TV-digitizer system was developed. As an example, both image and overall quality indices were evaluated on three mammographic systems which are typical of the three different "phases" of the development of this technique.
从理论和实验角度来看，对射线照相胶片 - 增感屏系统进行比较评估存在若干问题。从理论角度而言，主要困难在于选择最适合表达系统“整体质量”的参数。从实际角度来看，主要问题是测量一些基本量（分辨率和噪声）需要精密且昂贵的仪器。本文探讨了这两个问题。为了表达图像质量，我们采用了信噪功率比：该指标明确取决于系统的对比度、分辨率和噪声。对灵敏度的依赖是隐含的，是通过文献数据推导得出的。基于对图像质量与灵敏度之间依赖关系的了解，有可能开发出一个“整体质量”指标，该指标被认为可以表达系统的“技术水平”。此指标可用于不同系统的比较评估。在这项工作中，使用标准仪器评估了一些基本物理量（特性曲线、灵敏度）。为了测量空间分辨率和噪声，开发了一种基于个人电脑的廉价电视数字化仪系统。例如，在三种典型的代表该技术发展三个不同“阶段”的乳腺摄影系统上评估了图像和整体质量指标。
