Assessment of detective quantum efficiency: intercomparison of a recently introduced international standard with prior methods.

PURPOSE

To prospectively evaluate the recently introduced international standard method for measurement of the detective quantum efficiency (DQE) of digital radiography systems, in comparison with representative prior methods.

MATERIALS AND METHODS

A recently introduced international standard method (International Electrotechnical Commission [IEC] 62220-1, 2003) for DQE measurement and two previously described DQE evaluation methods were considered. In addition to an overall comparison, evaluations of the following method factors were performed: beam quality, beam-limiting devices (apertures or collimators), noise power spectrum (NPS) analysis algorithms and parameters (area, region of interest size, background detrending), and modulation transfer function (MTF) test devices and methods.

RESULTS

Overall, at low to middle frequencies, the IEC method yielded DQE estimates that were 3.3% and 6.5% lower than the values yielded by the two previous methods. Averaged over the frequency range of 1.5-2.5 mm(-1), the DQE estimate derived by using the IEC method was 7.1% lower and 12.4% higher than the estimates derived by using the other two methods. Results obtained with the two previous DQE evaluation methods agreed well (within 2.0%) in the low- to middle-frequency range but diverged by up to 10% at higher frequencies. When the DQE method factors were evaluated separately, the largest percentage deviations in DQE were associated with (in order of decreasing influence) the MTF analysis method ( approximately 11%), the beam limitation (about 7%-10%), the beam quality ( approximately 9%), and the NPS analysis method ( approximately 3%).

CONCLUSION

Comparison of DQE estimates obtained by using the recently introduced international standard technique with those obtained by using prior methods revealed that the overall measurement method can affect the DQE estimate by as much as 12%. Findings further suggest that both beam limitation achieved by means of internal collimation (rather than external apertures) and use of a radio-opaque edge MTF device yield a more accurate estimation of the DQE.