Accuracy validation of incident photon fluence on detective quantum efficiency in mammography

X-ray image evaluation is commonly performed by determining the detective quantum efficiency (DQE). DQE is calculated with a presampled modulation transfer function (MTF), incident photon fluence, and digital noise power spectrum (NPS). Accurate evaluation of MTF, incident photon fluence, and NPS is important for precise DQE determination. In this study, we focused on the accuracy of the incident photon fluence in mammography. The incident photon fluence is calculated using the squared signal-to-noise ratio (SNR_in²) value as specified in the International Electrotechnical Commission (IEC) 62220-1-2 report. However, the reported SNR_in² values were determined using a computer program, and the reported values may differ from those calculated from an X-ray spectrum that is measured with actual mammography equipment. Therefore, we evaluated the error range of reported SNR_in² values in mammography to assess the accuracy of the incident photon fluence. First, X-ray spectra from various mammography systems were measured with a CdTe spectrometer. Six mammographic X-ray units were used in this study. Second, the SNR_in² values were calculated from the measured X-ray spectra. The calculated values were compared to the reported values. The results show that the percentage differences between the calculated and reported SNR_in² values were within - 4.1% of each other. The results obtained in this study indicate that the SNR_in² values provided in the IEC report are a robust and convenient tool for calculating the incident photon fluence for DQE evaluation in mammography.