Evaluation of Different Modulation Transfer Function Measurement Based on Different Edge Spread Function Calculations

Purpose: As the X-ray imaging market keeps expanding and digital X-ray detector technology has become more important, the International Electro Technical Commission has developed an IEC 62220-1 standard for the device to cope with medical imaging report requirements. This paper specifies the modulation transfer function (MTF) and detective quantum efficiency (DQE) calculation method. However, during the practical operation, we found that if the multiple pre-sampling edge spread functions (ESFs) were averaged directly, the MTF value would be underestimated. This work develops a novel method for calculating the MTF. Methods: We compared three different edge spread function (ESF) calculation methods. For method 1, the ESF is obtained by taking only the central line. For method 2, the ESFs are averaged directly. For method 3, the novel method proposed in this study, the ESFs would be shifted before they are averaged. The MTF is then obtained through calculating three different ESFs. Results: We used a phantom experiment to verify the correctness of the code and confirm the results from the three methods under ideal conditions. We measured the detector response through a homemade laboratory testing platform. The results showed that, method 3 effectively eliminated MTF underestimation. The difference was not significant when the frequency was less than 1.5 lp/mm, however when it was greater than 1.5 lp/mm, the difference was larger. Conclusions: This finding suggests that to eliminate the results caused by noise without any signal processing, and to generate a smoother MTF, our proposed method can give much reliable results.