抄録
For the purpose of measuring the grayed degree in X-ray films, the evaluation of the subject has been conducted by the digital image processing (DIP) method utilizing high accuracy of aluminum steps and slopes for the calibration of the DIP system. The aluminum reference device must have a high dimensional accuracy and good reproducibility of nearly identical measurement values. The accuracy of this radiographic reference device was studied by comparatively measuring the aluminum thickness and equivalent values. The following are the results of this study.
1. The comparison between the aluminum step's thickness and measured equivalent values, with the measurement taken using the steps of the device as a reference, found that the relative errors between them averaged 0.9%. This level of error was almost the same as the average relative error value of 1.0% obtained regarding the slopes of the reference device.
2. A similar comparison between the aluminum slope's thickness and equivalent values produced an average relative error of 8.0%. On the other hand, a comparison between the aluminum step's thickness and equivalent values, when measurement was taken using the slope of the aluminum device as a reference, obtained a comparatively large average relative error of 9.3%, indicating poor accuracy of the device.
3. The comparison of the length of DIP system manipulation time required before obtaining the standard curve values between the aluminum step and aluminum slope measurements found that the latter had a 50-second shorter time (p＜0.01) than the former.
4. However, it has been found that the aluminum step measurement is superior to the aluminum slope counterpart in measurement accuracy and the reproducibility of measured values.
5. The aluminum step scheme makes it possible to conduct measurement under equivalent conditions even when measurement samples of different sizes are involved.
