[Quantitative evaluation of X-ray opacity of the maxillary sinus using a digital disposition system]

The authors attempted to obtain a quantitative index of X-ray opacity of the maxillary sinus using a digital disposition system. X-ray films of the Waters' view were used for analysis. A cooper wedge was placed on the left side of the subject's face and was simultaneously filmed. The wedge was made of copper plates increased in thickness from 0.2 to 4.0 mm in 20 steps and serving as a calibration standard. The subject-to-film distance was kept constant at one meter. The voltage and current of the X-ray tube were 85 kV and 200 mA, respectively. The X-ray films were digitized with a film-digitizer (Toshiba, TDF-500B). The X-ray opacity from 0.0 to 4.0 was transformed to 1024 steps and the whole X-ray film was divided into 512 x 512 pixels. Then, the X-ray density of each pixel was converted to an absolute value of wedge thickness with a medical image processor (Toshiba, GMS-500U). The mean pixel values in the region of interest (ROI) of the maxillary sinus and that of the whole maxillary sinus were named MR and MW, respectively. The mean pixel value in the ROI of the ipsilateral orbita was called O. We used MR, MW, MR -O and MW -O as indices. The results were as follows: 1. MR, MW, MR -O and MW -O were useful in quantitative evaluation of the X-ray opacity of the maxillary sinus in a subject. 2. MR -O and MW -O were also good references for comparing the X-ray opacity of the maxillary sinus among different subjects.